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Purpose: The purpose of this work was to detail our center's experience in transitioning from a Co-60 treatment technique to an intensity modulated radiation therapy (IMRT) based lateral-field extended source-to-axis distance (e-SAD) technique for total body irradiation (TBI)., Materials and Methods: An existing beam model in RayStation v.10A was validated for the use of e-SAD TBI treatments. Data were acquired with an Elekta Synergy linear accelerator (LINAC) at an extended source-to-surface distance of 365 cm with an 18 MV beam. Beam model validation measurements included percentage depth dose (PDD), profile data, surface dose, build-up region and transmission measurements. End-to-end testing was carried out using an anthropomorphic phantom. Treatments were performed in a supine position in a whole-body Vac-Lok at an e-SAD of 400 cm with a beam spoiler 10 cm from the couch. Planning was achieved using IMRT, where multi-leaf collimators were used to modulate the beam and shield the organs at risk. Beam's eye view projection images were used for in-room patient positioning and in-vivo dosimetry was performed for every treatment., Results: The percent difference between the measured and calculated PDD and profiles was less than 2% at all locations. Surface dose was 83.8% of the maximum dose with the beam spoiler at a 10 cm distance from the phantom. The largest percent difference between the treatment planning system (TPS) and measured data within the anthropomorphic phantom was approximately 2%. In-vivo dosimetry measurements yielded results within the 5% institutional threshold., Conclusion: In 2022, 17 patients were successfully treated using the new IMRT-based lateral-field e-SAD TBI technique. The resulting clinical plans respected the institutional standard. The commissioning process, as well as the treatment planning and delivery aspects were described in this work with the intention of supporting other clinics in implementing this treatment method., (© 2024 The Author(s). Journal of Applied Clinical Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.)

Background: High dose rate (HDR) image-guided brachytherapy with Cobalt-60 isotope is a relatively recent approach. The aim of the study is to evaluate the clinical and dosimetric parameters in terms of tumour response, bladder, and rectal toxicity in patients undergoing Co-60 HDR brachytherapy., Materials and Method: All patients were initially treated with chemoradiation (CT-RT) at our center or other referral centers with external beam radiation therapy (EBRT) for a dose of 45 Gy-60 Gy at 1.8-2Gy/fraction (including nodal boost) with concomitant chemotherapy with either cisplatin or carboplatin. Patients were then scheduled for brachytherapy within 1 week after completion of CT-RT and are assessed by local examination. Depending on local examination parameters at the time of brachytherapy they were eligible either for intracavitary brachytherapy (ICBT) or interstitial brachytherapy (ISBT)., Results: The complete response (CR) observed in stage I, II, III, IVA were 60%, 79.4%, 86% and 76.2% respectively. Complete response was seen in patients with mean EQD2 of 78.67 Gy 10 , 83.33 Gy 10 , 84.23 Gy 10 , 85.63 Gy 10 in stages I, II, III, IVA respectively. 79.2% of cisplatin-treated patients and 87.5% of carboplatin-treated patients had a complete response indicating that patients treated with either chemotherapy had similar response rates., Conclusions: According to results obtained from the study we conclude by saying that higher rates of complete response to treatment in cervical cancer is seen in patients with shorter overall treatment time (OTT), shorter interval between end of definitive CT-RT and beginning of brachytherapy and squamous cell histology. The study also noted the trend of increasing mean EQD2 to tumor with increasing stage for achieving complete response. Higher acute bladder and rectal toxicity is seen in patients who received EQD2 of ¿70-90Gy 3 and ¿70Gy 3 respectively. The study findings suggest that the clinical outcomes and the toxicities are clinically comparable with other radioisotope based HDR brachytherapy treatment., Competing Interests: The authors declare there are no competing interests., (©2024 Makkapati et al.)

Background and Purpose: The impact of cobalt-60 dose rate (Co-60 DR) on outcomes of stereotactic radiosurgery (SRS) for brain arteriovenous malformations (AVMs) remains fully elucidated. This study explored the association between Co-60 DR and SRS outcomes in AVM treatment., Materials and Methods: 772 AVM patients from 1990 to 2020 were included. High DR was defined as ≥ 2.4 Gy/min. AVM patients were categorized into 3 cohorts based on the nidus volume: small (<5 mL), medium (≥5 mL and < 10 mL), and large (≥10 mL). The primary endpoint was AVM obliteration; secondary endpoints included post-SRS hemorrhage., Results: Cumulative obliteration rates of the large AVM were significantly increased in the high DR group than those in the low DR group (84 % vs. 45 % at 5 years, log-rank test; p = 0.011). Multivariable analysis showed that the obliteration rate was significantly elevated for the high DR group in the large AVM cohort with an adjusted hazard ratio (HR) of 1.78 (95 % confidence interval [CI]: 1.00-3.17, p = 0.049). Post-SRS hemorrhage rates of the entire cohort were significantly decreased in the high DR group than in the low DR group (2.5 % vs. 5.3 % at 5 years, log-rank test; p = 0.035). Multivariable analysis revealed post-SRS hemorrhage was reduced in the high DR group with an adjusted HR of 0.47 (95 % CI: 0.24-0.92, p = 0.026)., Conclusion: High DR may lead to increased efficiency for large AVMs and decreased post-SRS hemorrhage in all AVM cases. Sustaining a higher Co-60 DR could potentially yield favorable outcomes for SRS for AVMs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Introduction: High dose rate (HDR) intracavitary brachytherapy (ICBT) is an integral element in the treatment of carcinoma uterine cervix. The main objective of brachytherapy in carcinoma cervix is to deliver a lethal dose to tumor cells without inducing unacceptable damage to the surrounding normal tissue. Because the absorbed dose falls off rapidly, higher doses can be safely delivered to the targeted tissue over a short time. The quest for optimum dose and fractionation schedule in HDR ICBT is still ongoing, and there is no uniform consensus. This study aimed to assess the acute dose-related toxicities of HDR brachytherapy schedule of 7 Gy x 3 fractions over 6 Gy x 4 fractions in the treatment of cervical cancer., Objective: The aim of this study was to study the acute treatment-related gastrointestinal (GI) and genitourinary (GU) toxicities between two HDR brachytherapy regimens., Material and Methods: This is a prospective institutional study carried out from May 2018 to September 2018. In this time period, 66 patients of cervical cancers fulfilling our inclusion criteria were treated with concurrent chemoradiation (CCRT) following brachytherapy. During treatment, patients were randomized to arm A-7 Gy per fraction for three fractions and arm B-6 Gy per fraction for four fractions. Acute GI and GU toxicities were assessed using Common Terminology Criteria for Adverse Events (CTCAE) Version 4.03. All patients were kept for follow-up for 3 months in this study., Results: There is no statistically significant difference between the two arms for acute GI and GU toxicities, and the results were comparable., Conclusions: Considering the increased hospital burden of locally advanced cervical cancer patients in the Indian context, the HDR brachytherapy schedule of 7 Gy per fraction is preferable to 6 Gy per fraction for a lesser fractionation schedule., (Copyright © 2024 Copyright: © 2024 Journal of Cancer Research and Therapeutics.)

Background: Non-melanoma skin cancer is one of the most common types of cancer and one of the main approaches is brachytherapy. For small lesions, the treatment of this cancer with brachytherapy can be done with two commercial applicators, one of these is the Large Field Valencia Applicators (LFVA)., Purpose: The aim of this study is to test the capabilities of the LFVA to use clinically 60 Co sources instead of the 192 Ir ones. This study was designed for the same dwell positions and weights for both sources., Methods: The Penelope Monte Carlo code was used to evaluate dose distribution in a water phantom when a 60 Co source is considered. The LFVA design and the optimized dwell weights reported for the case of 192 Ir are maintained with the only exception of the dwell weight of the central position, that was increased. 2D dose distributions, field flatness, symmetry and the leakage dose distribution around the applicator were calculated., Results: When comparing the dose distributions of both sources, field flatness and symmetry remain unchanged. The only evident difference is an increase of the penumbra regions for all depths when using the 60 Co source. Regarding leakage, the maximum dose within the air volume surrounding the applicator is in the order of 20% of the prescription dose for the 60 Co source, but it decreases to less than 5% at about 1 cm distance., Conclusions: Flatness and symmetry remains unaltered as compared with 192 Ir sources, while an increase in leakage has been observed. This proves the feasibility of using the LFVA in a larger range of clinical applications., (© 2024 American Association of Physicists in Medicine.)

This work presents the dosimetric characteristics of Total Body Irradiation (TBI) delivered using a dedicated Co-60 TBI unit. We demonstrate the ability to deliver a uniform dose to the entire patient without the need for a beam spoiler or patient-specific compensation. Full dose distributions are calculated using an in-house Monte Carlo treatment planning system, and cumulative dose distributions are created by deforming the dose distributions within two different patient orientations. Sample dose distributions and profiles are provided to illustrate the plan characteristics, and dose and DVH statistics are provided for a heterogeneous cohort of patients. The patient cohort includes adult and pediatric patients with a range of 132-198 cm in length and 16.5-37.5 cm in anterior-posterior thickness. With the exception of the lungs, a uniform dose of 12 Gy is delivered to the patient with nearly the entire volume receiving a dose within 10% of the prescription dose. Mean lung doses (MLDs) are maintained below the estimated threshold for radiation pneumonitis, with MLDs ranging from 7.3 to 9.3 Gy (estimated equivalent dose in 2 Gy fractions (EQD 2 ) of 6.2-8.5 Gy). Dose uniformity is demonstrated across five anatomical locations within the patient for which mean doses are all within 3.1% of the prescription dose. In-vivo dosimetry demonstrates excellent agreement between measured and calculated doses, with 78% of measurements within ±5% of the calculated dose and 99% within ±10%. These results demonstrate a state-of-the-art TBI planning and delivery system using a dedicated TBI unit and hybrid in-house and commercial planning techniques which provide comprehensive dosimetric data for TBI treatment plans that are accurately verified using in-vivo dosimetry., (© 2023 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.)

Purpose: A novel compensator-based system has been proposed which delivers intensity-modulated radiation therapy (IMRT) with cobalt-60 beams. This could improve access to advanced radiotherapy in low- and middle-income countries. For this system to be clinically viable and to be adapted into the Radiation Planning Assistant (RPA), being developed to offer automated planning services in low- and middle-income countries, it is necessary to commission and validate it in a commercial treatment planning system (TPS)., Methods: The novel treatment device considered here employs a cobalt-60 source and nine compensators. Each compensator is produced by 3-D printing a thin plastic mold which is then filled on-demand within the machine with reusable 2-mm-diameter spherical tungsten balls. This system was commissioned in the Eclipse TPS and validation tests were conducted with Monte Carlo using Geant4 Application for Tomographic Emission for percentage depth dose, in-plane profiles, penumbra, and IMRT dose validation. And the American Association of Physicists in Medicine Task Group 119 benchmarking testing was performed. Additionally, compensator-based cobalt-60 IMRT plans were created for 46 head-and-neck cancer cases and compared to the linac-based volumetric modulated arc therapy (VMAT) plans used clinically, then dosimetric parameters were evaluated. Beam-on time for each field was calculated. In addition, the measurement was also performed in a limited environment and compared with the Monte Carlo simulations., Results: The differences in percent depth doses and in-plane profiles between the Eclipse and Monte Carlo simulations were 0.65% ± 0.41% and 1.02% ± 0.99%, respectively, and the 80%-20% penumbra agreed within 0.46 ± 0.27 mm. For the Task Group 119 validation plans, all treatment planning goals were met and gamma passing rates were >95% (3%/3 mm criteria). In 46 clinical head-and-neck cases, the cobalt-60 compensator-based IMRT plans had planning target volume (PTV) coverages similar to linac-based VMAT plans: all dosimetric values for PTV were within 1.5%. The organs at risk dose parameters were somewhat higher in cobalt-60 compensator-based IMRT plans versus linac-based VMAT plans. The mean dose differences for the spinal cord, brain, and brainstem were 4.43 ± 1.92, 3.39 ± 4.67, and 2.40 ± 3.71 Gy, while those for the rest of the organs were <1 Gy. The average beam-on time per field was 0.42 ± 0.10 min for the 6 MV multi-leaf-collimator plans while those for the cobalt-60 compensator plans were 0.17 ± 0.01 and 0.31 ± 0.01 min at the dose rates of 350 and 175 cGy/min. There was a good agreement between in-plane profiles from measurements and Monte Carlo simulations, which differences are 1.34 ± 1.90% and 0.13 ± 2.16% for two different fields., Conclusions: A novel compensator-based IMRT system using cobalt-60 beams was commissioned and validated in a commercial TPS. Plan quality with this system was comparable to that of linac-based plans in all test cases with shorter estimated beam-on times. This system enables reliable, high-quality plans with reduced cost and complexity and may have benefits for underserved regions of the world. This system is being integrated into the RPA, a web-based platform for auto-contouring and auto-planning., (© 2023 American Association of Physicists in Medicine.)

Background: High-dose-rate (HDR) intracavitary-interstitial brachytherapy (IC-ISBT) is an effective treatment for bulky, middle, and advanced cervical cancer. In this study, we compared the differences between 60Co and 192Ir HDR IC-ISBT plans in terms of radiobiological and dosimetric parameters, providing a reference for clinical workers in brachytherapy., Methods: A total of 30 patients with cervical cancer receiving HDR IC-ISBT were included in this study, and IC-ISBT plans for each individual were designed with both 60Co and 192Ir at a prescribed dose of CTV D90 = 6 Gy while keeping the dose to OARs as low as possible. Physical dose and dose-volume parameters of CTV and OARs were extracted from TPS. The EQD2, EUBED, EUD, TCP, and NTCP were calculated using corresponding formulas. The differences between the 60Co and 192Ir IC-ISBT plans were compared using the paired t-test., Results: In each patient's 60Co and 192Ir IC-ISBT plan, the average physical dose and EQD2 of 60Co were lower than those of 192Ir, and there were statistically significant differences in D2cc and D1cc for the OARs (p < 0.05); there were statistically significant differences in D0.1 cc for the bladder (p < 0.05) and no significant differences in D0.1 cc for the rectum or intestines (p > 0.05). The EUBED ratio (60Co/192Ir) at the CTV was mostly close to 1 when neither 60Co or 192Ir passed their half-lives or when both passed two half-lives, and the difference between them was not significant; at the OARs, the mean value of 60Co was lower than that of 192Ir. There was no statistical difference between 60Co and 192Ir in the EUD (93.93 versus 93.92 Gy, p > 0.05) and TCP (97.07% versus 97.08%, p > 0.05) of the tumors. The mean NTCP value of 60Co was lower than that of 192Ir., Conclusions: Considering the CTV and OARs, the dosimetric parameters of 60Co and 192Ir are comparable. Compared with 192Ir, the use of 60Co for HDR IC-ISBT can ensure a similar tumor control probability while providing better protection to the OARs. In addition, 60Co has obvious economic advantages and can be promoted as a good alternative to 192Ir., (© 2022. The Author(s).)

Magnetic resonance imaging (MRI) during brachytherapy may alter the dose distribution of radioactive sources implanted in the tumor. This study investigates the impact of a magnetic field of 1.5 T, 3 T, and 7 T strengths on the dose distribution of high dose rate Co-60, Ir-192, and Yb-169, and low dose rate I-125 sources, using Geant4 Monte Carlo toolkit. After validating the simulation results by calculating the AAPM-TG43 dosimetric parameters, seven sources of each radioisotope were simulated in a water phantom, and their dose distributions were compared under the influence of a magnetic field. The simulation results indicate that using Co-60 brachytherapy under the MRI guidance is not recommended. Furthermore, the impact of a magnetic field of up to 7 T strength on the dose distribution of Ir-192, Yb-169, and I-125 sources is negligible, provided that there is no air pocket near brachytherapy sources., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: The aim of our study is to assess the dose enhancement from scattered radiation due to dental restorative materials used for occlusal and mesio-occlusal-distal (MOD) cavity filling during simulated head and neck radiotherapy., Methods: We have studied the dose enhancement ratio (DER) of conventional amalgam, high-copper amalgam, and resin composite dental restorative materials at cadaver mandible teeth using 2 therapeutic photon energies of 1.25 MeV (Co-60 gamma ray) and 6 MV (Linac X-ray) for irradiation., Results: DER values at buccal position for Co-60 and 6 MV X-ray were 1.250 ± 0.013 and 1.151 ± 0.012, respectively. For dental cavity fillings, DER values for 6 MV X-ray were 1.065 ± 0.021, 1.100 ± 0.014, and 1.162 ± 0.016 for resin composite filling, low-copper amalgam filling, and high-copper amalgam filling, respectively. Our results revealed that DER regarding irradiation energy was minimum for 6 MV X-rays. With respect to dental restorative filling material, DER was minimum for resin composite filling. Regarding the cavity type, our results with standard deviation (SD) calculations revealed that DER was slightly but not significantly different for both Co-60 gamma ray (1.25 MeV) and 6 MV X-ray energies for both occlusal and MOD cavities., Conclusion: Our dosimetric results for a single beam geometry suggest that, among the three types of filling, resin composite filling is an ideal restorative filling material with minimal morbidity-inducing radiation dose enhancement that may result in increased osteoradionecrosis and secondary caries risk. There is a need for further dosimetric studies with actual clinical beam arrangements., Competing Interests: None

Purpose: This study investigated the correlation between the prescription dose and dose to the Manchester and International Commission on Radiation Units and Measurements-report 38 (ICRU-38) lymphatic trapezoid points during high-dose-rate (HDR) brachytherapy of locally advanced cervical cancer with (Cobalt-60) 60Co ., Methods and Materials: A retrospective study was designed for; patients with locally advanced cervical cancer, treated by external beam radiotherapy and concurrent weekly Cisplatin-based chemotherapy, had no extended parametrial invasion and was treated by tandem-ovoid set, from 2017 to 2020. Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) based target's volume, ICRU-89 revised version of Manchester points A and B, and ICRU-38 lymph node surrogate points were determined, and their dose was recorded. Paired sample t-test, linear regression analysis, and Pearson correlation analyses were done considering a statistical significance level of 0.05 and using IBM SPSS statistics (Version 23, IBM Crop.)., Results: Seventy-four brachytherapy cases were included. A positive and strong correlation was observed between D 90 of clinical target volume (CTV HR ) and points A and B dose for CTV HR 〈 15 cc and 〉 35 cc. Strong and significant (p < 0.05) correlations were achieved between pelvic wall points dose and D 90 and D 100 of the obturator and between D 50 and hot points of internal iliac lymph nodes. A strong correlation was obtained between D 50 and D 90 of external iliac lymph nodes and their ICRU points., Conclusions: Strong correlations were obtained between dose to the pelvic lymphatic chains and their historical ICRU-38 surrogate points during HDR brachytherapy of locally advanced cervical cancer patients with 60Co tandem-ovoid applicator sets. The correlation strength between point A and prescription dose highly depends on the CTV HR volume., (Copyright © 2021 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Introduction: Combination of external beam radiotherapy (EBRT) and High Dose Rate (HDR) brachytherapy (BT) with concurrent chemotherapy (Cisplatin 40mg/m2/weekly) is the standard treatment of approach for the carcinoma of uterine cervix. In this study for image based HDR brachytherapy of intracavitary both 192Ir and 60Co sources were used for dosimetry and the dose distribution compared between point doses and volume doses as per the recommendation of ICRU89 and GEC-ESTRO on 3D image based planning. The dosimetry and clinical outcome will decide decisionmaking on choice of radionuclide for HDR brachytherapy of cervix in addition to economic reason., Materials and Methods: The Study conducted for 27 patients of cancer cervix stage IIB or IIIB with vaginal involvement limited to the upper third of vagina. All patients underwent concurrent chemoradiation Cisplatin 40mg/m2 weekly throughout EBRT by 3D conformal therapy 46Gy in 23# followed by two fractions of HDR brachytherapy with 9Gy/1Fr. Post implants 3mm slice selection of pelvic CT scans performed with ring applicator in place followed by T2 weighted paracorpal or paracoronal section of MRI imaging. The solid ring applicator (AL13017000) from library used for applicator reconstruction. Initially all plan calculated with TG-43 formalism using 192Ir radionuclide (Varian, GammaMed HDR Plus source) and then modelled 60Co radionuclide (Eckert < Ziegler BEBIG GmbH, Co0. A86) used for dose computation. ICRU89 recommended points and volumes of targets and OARs evaluated and compared., Results: The study concludes that 60Co based point-A, BICRU and RICRU doses showed a comparable result with that of 192Ir HDR source based dosimetry. The volume based criterion for the target such as GTV, CTVHR, CTVIR for D90, D98, V150%and V200% are all within 5% dose level comparing two sources., Conclusion: 60Co a viable alternate to 192Ir by taking into consideration frequency of source exchange and cost reserve with comparable dosimetry.

Background: We aim to assess the risks associated with total body irradiation (TBI) delivered using a commercial dedicated Co-60 irradiator, and to evaluate inter-institutional and inter-professional variations in the estimation of these risks., Methods: A failure mode and effects analysis (FMEA) was generated using guidance from the AAPM TG-100 report for quantitative estimation of prospective risk metrics. Thirteen radiation oncology professionals from two institutions rated possible failure modes (FMs) for occurrence (O), severity (S), and detectability (D) indices to generate a risk priority number (RPN). The FMs were ranked by descending RPN value. Absolute gross differences (AGD) in resulting RPN values and Jaccard Index (JI; for the top 20 FMs) were calculated. The results were compared between professions and institutions., Results: A total of 87 potential FMs (57, 15, 10, 3, and 2 for treatment, quality assurance, planning, simulation, and logistics respectively) were identified and ranked, with individual RPN ranging between 1-420 and mean RPN values ranging between 6 and 74. The two institutions shared 6 of their respective top 20 FMs. For various institutional and professional comparison pairs, the number of common FMs in the top 20 FMs ranged from 6 to 13, with JI values of 18-48%. For the top 20 FMs, the trend in inter-professional variability was institution-specific. The mean AGD values ranged between 12.5 and 74.5 for various comparison pairs. AGD values differed the most for medical physicists (MPs) in comparison to other specialties i.e. radiation oncologists (ROs) and radiation therapists (RTs) [MPs-vs-ROs: 36.3 (standard deviation SD = 34.1); MPs-vs-RTs: 41.2 (SD = 37.9); ROs-vs-RTs: 12.5 (SD = 10.8)]. Trends in inter-professional AGD values were similar for both institutions., Conclusion: This inter-institutional comparison provides prospective risk analysis for a new treatment delivery unit and illustrates the institution-specific nature of FM prioritization, primarily due to operational differences. Despite being subjective in nature, the FMEA is a valuable tool to ensure the identification of the most significant risks, particularly when implementing a novel treatment modality. The creation of a bi-institutional, multidisciplinary FMEA for this unique TBI technique has not only helped identify potential risks but also served as an opportunity to evaluate clinical and safety practices from the perspective of both multiple professional roles and different institutions., (© 2021. The Author(s).)

Background: Application of the most advanced radiation technologies of brachytherapy featuring the high dose ratesources i.e. 60Co and 192Ir within contemporary management protocols for gynecological cancer provides maximum dosedistribution in the clinical target along with minimal radiation exposure on surrounding organs and tissues. It involvesirradiation of large spaces with delivery of high therapeutic doses at the tolerance bound of «critical» organs (bladder,rectum) and tissues. Thus minimization of the early and late radiation complications, life span extent and quality oflife increase remain just the issues in contemporary radiation oncology requiring therefore the elaboration of radiobiological criteria along with substantiation of physiсо-engineering properties of the radiation sources. Taking intoaccount the basic radiobiological patterns will ensure a definitive further progress in the field of radiation oncology., Objective: to study and compare the biological effects of 192Ir with the effects of the reference gamma radiation 60Coand increase the effectiveness of brachytherapy using a 192Ir source., Materials and Methods: Radiobiological dosimetry on the basis of a test system of peripheral blood lymphocytesfrom the gynecological cancer patients with subsequent cytogenetic analysis of radiation-induced chromosomeaberrations was performed to study and compare the biological effects of 192Ir and reference 60Со γ-radiation, and toenhance the efficiency of 192Ir brachytherapy., Results: Radiation markers, i.e. dicentric chromosomes with an accompanying paired fragment prevailed in thespectrum of radiation-induced damage. Variability of individual cytogenetic parameters of peripheral lymphocytesupon the first fraction of irradiation at the same dose of 5 Gy indicated an individual sensitivity of patients to the192Ir γ-irradiation. Comprehensive conservative treatment with adjuvant radiotherapy was applied to the patients(n = 98) having got secondary vaginal cancer stage II-III, T2-3N0-1M0. The high dose-rate (HDR) brachytherapy using 192Ir radiation sources was applied in the main study group (n = 37), HDR brachytherapy using 60Co radiation sourceswas applied in the control group (n = 35)., Conclusion: The HDR brachytherapy with 192Ir and 60Co sources on the up-to-date technology intensive devices provides a high accuracy of dose distributions when irradiating the malignant neoplasms with minimized radiationexposure to the «critical» tissues. Treatment results are improved therefore. The use of 192Ir radiation sources compared with 60Co ones resulted in an increased throughput of treatment, enhanced tumor regression, and reduced incidence of radiation effects on the critical organs. Currently we perform the radiobiological studies on somatic cellsfrom cancer patients at the genetic, biochemical, biophysical, and cytological levels in order to receive a biologicalindication of radiation damage under the impact of 192Ir isotope. Continuation of clinical trials with radiobiologicalsupport will provide an opportunity to predict the early and late radiation complications and thus to provide a personalized approach in brachytherapy of cancer patients using the 192Ir sources of γ-rays., (V. S. Ivankova, E. A. Domina, T. V. Khrulenko, L. M. Baranovska, O. O. Hrinchenko.)

Background/aim: The cell-killing and radiosensitizing effects of carbon-ion (C-ion) beams with low linear energy transfer (LET) are underexplored. We aimed to demonstrate the cell-killing effects of 60 Co gamma rays and C-ion beams at various LET values and the radiosensitizing effect of C-ion beams at various LET and cisplatin levels., Materials and Methods: Human uterine cervical cancer cells were irradiated with 60 Co gamma rays and C-ion beams at different levels of LET, with and without cisplatin treatment., Results: Low-LET C-ion beams had a superior cell-killing effect compared to 60 Co gamma rays. Survival curves under low-LET C-ion beams were more similar to that of 60 Co gamma rays than that of high-LET C-ion beams. Cisplatin significantly reduced cell survival after 1, 2, and 3 Gy C-ion beam irradiations at LET values of 13/30/70 keV/μm, 13/30 keV/μm, and 13 keV/μm, respectively., Conclusion: Low-LET C-ion beams combined with cisplatin have higher radiosensitizing effects than high-LET C-ion beams., (Copyright© 2020, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Purpose: This is a study of our experience with Co-60 high dose rate brachytherapy (HDR BT) from a tertiary care center., Materials and Methods: One thousand patients were treated with Cobalt-based HDR BT for more than 6 years. The practice of BT was analyzed for clinical outcome, physical, radiobiological, and technical aspects., Results: Among those 1000 patients, 906 (90.6%) patients had gynecologic cancer, 29 (2.9%) patients had intraluminal BT, 63 (6.3%) hadhead &neck (2.1%), keloid (2.1%) and mold BT (2.1%), and 2 (0.2%) had sarcoma. Dose rate decreased by 48.9%, and treatment time increased from 9.33 to 18.27 min over 5 years. No patients treatment was abandoned because of machine-related problems., Conclusion: Cobalt-based HDR BT is preferable in terms of lesser source exchanges, relatively uniform treatment time, quality assurance requirement, and cost., (Copyright © 2020 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

The Monte Carlo (MC) method is widely used to solve various problems in radiotherapy. There has been an impetus to accelerate MC simulation on GPUs whereas thread divergence remains a major issue for MC codes based on acceptance-rejection sampling. Inverse transform sampling has the potential to eliminate thread divergence but it is only implemented for photon transport. Here, we report a MC package Particle Transport in Media (PTM) to demonstrate the implementation of coupled photon-electron transport simulation using inverse transform sampling. Rayleigh scattering, Compton scattering, photo-electric effect and pair production are considered in an analogous manner for photon transport. Electron transport is simulated in a class II condensed history scheme, i.e., catastrophic inelastic scattering and Bremsstrahlung events are simulated explicitly while subthreshold interactions are subject to grouping. A random-hinge electron step correction algorithm and a modified PRESTA boundary crossing algorithm are employed to improve simulation accuracy. Benchmark studies against both EGSnrc simulations and experimental measurements are performed for various beams, phantoms and geometries. Gamma indices of the dose distributions are better than 99.6% for all the tested scenarios under the 2%/2 mm criteria. These results demonstrate the successful implementation of inverse transform sampling in coupled photon-electron transport simulation.

Purpose: The aim of this work is to investigate the influence of an external magnetic field (MF) on The American Association of Physicists in Medicine (AAPM) No. 43 Report (TG-43) parameters for 192 Ir and 60 Co high dose rate (HDR) brachytherapy sources using Monte Carlo (MC) simulation methods., Materials and Methods: We used the Geant4 toolkit (version 10.1. p01) to simulate the geometry of 192 Ir and 60 Co brachytherapy sources. AAPM TG-43 parameters (the radial dose function, g(r), and the anisotropy function, F (r, θ)) of both 192 Ir and 60 Co sources were calculated in the presence of a magnetic field with strengths of 1.5T, 3T, and 7T in the X, Y, and Z directions in a voxelized water phantom., Results: For the 192 Ir source, the calculated values g(r) and F (r, θ) remained nearly unaffected by the magnetic field for all investigated strengths. For the 60 Co source, the differences for the g(r) and F (r,θ) under the 1.5T, 3T, and 7T magnetic field strengths along the direction parallel with the MF were found to be an increase of up to 5%, 15%, and 33%, respectively. However, for the directions perpendicular with the magnetic field, there was a decrease of up to 3%, 6% and 15% under 1.5T, 3T and 7T strengths, respectively., Conclusion: Our results highlight the necessity of a Monte Carlo-based treatment planning system (TPS) if cobalt HDR treatments are performed under a magnetic field, especially for strengths greater than 1.5T., Competing Interests: Declaration of competing interest There is no conflicts of interest., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Purpose: Several radionuclides with high ( 60 Co, 75 Se) and intermediate ( 169 Yb, 153 Gd) energies have been investigated as alternatives to 192 Ir for high-dose-rate brachytherapy. The purpose of this study was to evaluate the impact of tissue heterogeneities for these five high- to intermediate-energy sources in prostate and head & neck brachytherapy., Methods and Materials: Treatment plans were generated for a cohort of prostate (n = 10) and oral tongue (n = 10) patients. Dose calculations were performed using RapidBrachyMCTPS, an in-house Geant4-based Monte Carlo treatment planning system. Treatment plans were simulated using 60 Co, 192 Ir, 75 Se, 169 Yb, and 153 Gd as the active core of the microSelectron v2 source. Two dose calculation scenarios were presented: (1) dose to water in water (D w,w ), and (2) dose to medium in medium (D m,m )., Results: D w,w overestimates planning target volume coverage compared with D m,m , regardless of photon energy. The average planning target volume D 90 reduction was ∼1% for high-energy sources, whereas larger differences were observed for intermediate-energy sources (1%-2% for prostate and 4%-7% for oral tongue). Dose differences were not clinically relevant (<5%) for soft tissues in general. Going from D w,w to D m,m , bone doses were increased two- to three-fold for 169 Yb and four- to five-fold for 153 Gd, whereas the ratio was close to ∼1 for high-energy sources., Conclusions: D w,w underestimates the dose to bones and, to a lesser extent, overestimates the dose to soft tissues for radionuclides with average energies lower than 192 Ir. Further studies regarding bone toxicities are needed before intermediate-energy sources can be adopted in cases where bones are in close vicinity to the tumor., (Copyright © 2019 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

FLUKA-based Monte Carlo calculations were carried out to study microdosimetric distributions in air and in water for encapsulated high energy brachytherapy sources (60Co, 137Cs, 192Ir and 169Yb) by simulating a Tissue Equivalent Proportional Counter (Model LET1/2) having sensitive diameter of 1. 27 cm for a site size of 1 μm. The study also included microdosimetric distributions of bare sources. When the sources are in air, for a given source, the source geometry does not affect the y¯F and y¯D values significantly. When the encapsulated 192Ir, 137Cs and 60Co sources are in water, y¯F and y¯D values increase with distance in water which is due to degradation in the energy of photons. Using the calculated values of y¯D, relative biological effectiveness (RBE) was obtained for the investigated sources. When 60Co, 137Cs and 192Ir sources are in water, RBE increases from 1.03 ± 0.01 to 1.17 ± 0.01, 1.24 ± 0.01 to 1.46 ± 0.02 and 1.50 ± 0.01 to 1.75 ± 0.03, respectively, when the distance was increased from 3-15 cm, whereas for 169Yb, RBE is about 2, independent of distance in water., (© The Author(s) 2019. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Purpose: The aim of this study was to create an optical imaging-based system for quality assurance (QA) testing of a dedicated Co-60 total body irradiation (TBI) machine. Our goal is to streamline the QA process by minimizing the amount time necessary for tests such as verification of dose rate and field homogeneity., Methods: Plastic scintillating rods were placed directly on the patient treatment couch of a dedicated TBI 60 Co irradiator. A tripod-mounted intensified camera was placed directly adjacent to the couch. Images were acquired over a 30-s period once the cobalt source was fully exposed. Real-time image filtering was used; cumulative images were flatfield corrected as well as background and darkfield subtracted. Scintillators were used to measure light-radiation field correspondence, dose rate, field homogeneity, and symmetry. Dose rate effects were measured by modifying the height of the treatment couch and scintillator response was compared to ionization chamber (IC) measurements. Optically stimulated luminesce detector (OSLD) used as reference dosimeters during field symmetry and homogeneity testing., Results: The scintillator-based system accurately reported changes in dose rate. When comparing normalized output values for IC vs scintillators over a range of source-to-surface distances, a linear relationship (R 2  = 0.99) was observed. Normalized scintillator signal matched OSLD measurements with <1.5% difference during field homogeneity and symmetry testing. Beam symmetry across both axes of the field was within 2%. The light field was found to correspond to 90 ± 3% of the isodose maximum along the longitudinal and latitudinal axis, respectively. Scintillator imaging output results using a single image stack requiring no postexposure processing (needed for OSLD) or repeat manual measurements (needed for IC)., Conclusion: Imaging of scintillation light emission from plastic rods is a viable and efficient method for carrying out TBI 60 Co irradiator QA. We have shown that this technique can accurately measure field homogeneity, symmetry, light-radiation field correspondence, and dose rate effects., (© 2019 American Association of Physicists in Medicine.)

Aim: In the present study, surface doses within the target area and contralateral breast (CLB) received during conventional treatment of carcinoma breast are evaluate and compared for treatment on two different beam energies, i.e., Co-60 γ-ray and 6 MV X-ray beams with thermoluminescent dosimeter, LiF:Mg, Ti (TLD-100)., Materials and Methods: The study includes a group of 23 patients comprising 11 patients treated with Co-60 γ-ray beam and 12 patients by 6 MV X-ray beam., Results and Discussion: The treatment using Co-60 γ-ray and 6 MV X-ray beams contributes an average percentage dose of 8.15% ± 0.56% and 4.73% ± 0.94%, respectively, to CLB in mastectomy patients. The contribution of tangential fields (mastectomy) to the CLB doses ranges between 12.71 and 16.40 cGy (5.45%-7.03%) for treatment with Co-60 γ-ray beam and 6.33-10.95 cGy (1.86-4.69%) for treatment with 6 MV X-ray beam. The supraclavicular field (SCF) contributes 1.45%-1.93% and 1.02%-1.43% for treatment with Co-60 γ-ray and 6 MV X-ray beams, respectively. The average surface dose (normalized with breast dose) 89.1% ± 8.5% for Co-60 beam in the SCF region differs significantly from the 60.2% ± 13.0% value for 6 MV X-ray beam., Conclusion: The CLB doses for mastectomy patients are higher for Co-60 beam as compared to 6 MV X-ray beam, and better dose homogeneity is achieved within the irradiated breast from 6 MV X-ray beam. The CLB doses are slightly higher for patients treated with breast conservative radiotherapy or lumpectomy. The average surface dose to SCF decreases by ~30% of treated breast dose for treatment with 6 MV X-ray beam., Competing Interests: None

Purpose: The present work aimed to evaluate organ doses and related risk for cancer from external beam radiation treatment (EBRT) and high-dose-rate (HDR) brachytherapy (BT) involving Co-60 source for patients with cervical carcinoma in Tanzania based on Monte Carlo methods and to evaluate the secondary cancer risks in their lifetime., Methods: EBRT and HDR-BR were modelled by using the MCNPX Monte Carlo (MC) code. The MC simulations were performed by using validated models and isocentric irradiation of an adult female computational phantom. The organ doses and cancer risks estimates were obtained., Results: The highest absorbed doses of 6.98 × 10 -2 and 5.74 × 10 -2  Sv/Gy were recorded in the bladder for BT and EBRT. The higher risk was found for colon at 1.06 × 10 -3 in the HDR-BT and 9.75 × 10 -5 in the EBRT per 100,000 population at exposure age of 35 years than in the other organs. The risk magnitude decreased with increasing age at exposure. In general, the secondary cancer risks in all sites considered from EBRT and HDR-BR for cervical cancer patient were lower than the baseline risks., Conclusions: The chances of developing secondary cancer take years following radiation therapy are extremely low, but the results of present study can support to establish a future database on secondary cancer risks involving radiation therapy in patients with cervical cancer by using HDR-BR and EBRT with Co-60 source in Tanzania and other developing countries., (Copyright © 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Purpose: To establish a method of accurate dosimetry required to quantify the expected linear energy transfer (LET) quenching effect of EBT3 film used to benchmark the dose distribution for a given treatment field and specified measurement depth. In order to facilitate this technique, a full analysis of film calibration which considers LET variability at the plane of measurement and as a function of proton beam quality is demonstrated. Additionally, the corresponding uncertainty from the process was quantified for several measurement scenarios., Materials and Methods: The net change in optical density (OD) from a single version of Gafchromic TM EBT3 film was measured using an Epson flatbed scanner and NIST-traceable OD filters. Film OD response was characterized with respect to the known dose to water at the point of measurement for both a NIST-traceable 60 Co beam at the UWADCL and several clinical single-energy and spread-out Bragg peak (SOBP) proton beam qualities at the Northwestern Medicine Chicago Proton Center. Increasing proton LET environments were acquired by placing film at increasing depths of Gammex HE Solid Water® whose water-equivalent thickness was characterized prior to measurement., Results: A strong LET dependence was observed near the Bragg peak (BP) consistent with previous studies performed with earlier versions of EBT3 film. The influence of range straggling on the film's LET response appears to have a uniform effect toward the BP regardless of the nominal beam energy. Proximal to this depth, the film's response decreased with decreasing energy at the same dose-average LET. The opposite trend was observed for depths past the BP. Changes in the SOBP energy modulation showed a linear relationship between the film's relative response and dose-averaged LET. Relative effectiveness factors (RE) were observed to range between 2%-7% depending on the width of the SOBP and depth of the film. Using the field-specific calibration technique, a total k = 1 uncertainty in the absorbed dose to water was estimated to range from 4.68%-5.21%., Conclusion: While EBT3 film's strong LET dependence is a common problem in proton beam dosimetry, this work has shown that the LET dependence can be taken into account by carefully considering the depth and energy modulation across the film using field-specific corrections. RE factors were determined with a combined k = 1 uncertainty of 3.57% for SOBP environments and between 3.17%-4.69% for uniform, monoenergetic fields proximal to the distal 80% of the BP., (© 2019 American Association of Physicists in Medicine.)

Purpose: The present work reports effects of source step sizes on dose distribution in patients treated with cobalt-60 (Co-60) high-dose-rate afterloading brachytherapy in carcinoma cervix (Ca-cx)., Methods and Materials: The retrospective study is based on data of 15 patients of Ca-cx treated with Co-60 high-dose-rate intracavitary brachytherapy with dose of 21 Gy in three fractions with source step size of 2.5 mm after external beam radiotherapy of 46 Gy. The effect of source step size on overall treatment procedure was evaluated from prescribed dose volume, dose to organ at risks, and treatment time for source step sizes of 1 mm, 2.5 mm, 5 mm, and 10 mm for each patient., Results: The mean dose to bladder point for 1 mm, 2.5 mm, 5 mm, and 10 mm source step sizes was found to be 3.37 Gy (SD: 1.36), 3.44 Gy (SD: 1.38), 3.54 Gy (SD: 1.41), and 3.74 Gy (SD: 1.46), respectively. Similarly, the mean dose received by rectum point for these source step sizes were 2.86 Gy (SD: 0.64), 3.02 Gy (SD: 0.67), 3.25 Gy (SD: 0.71), and 3.63 Gy (SD: 0.73), respectively. The treatment time and prescribed dose coverage volume were both found to be gradually increasing with increase in step size., Conclusions: Our results on Ca-cx brachytherapy using Co-60 source indicate that the prescribed dose volume gradually increases from smaller source step to larger source step size. This results in increase of dose to the bladder and rectum and may lead to increase in toxicity and reduces quality of life. The study recommends that step size more than 5 mm should not be used for uterine cervix intracavitary application using Co-60 source., (Copyright © 2018 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

In vivo dosimetry in high dose-rate (HDR) intracavitary brachytherapy (ICBT) is important for assessing the true dose received by surrounding organs at risk during treatment. It also serves as part of the treatment delivery quality assurance and verification program with the use of a suitable dosimeter. Such a dosimeter should be characterized under brachytherapy conditions before clinical application to ensure the accuracy of in vivo measurement. In this study, a MOSFET-based detector, MOSkin, was calibrated and characterized under HDR Cobalt-60 (Co-60) brachytherapy source. MOSkin possessed the major advantages of having small physical and dosimetric sizes of 4.8 × 10 -6  mm 3 with the ability to provide real-time measurements. Using solid water and polymethyl methacrylate (PMMA) phantom, the detectors' reproducibility, linearity, angular and distance dependency was tested for its suitability as an in vivo detector. Correction factors to account for differences in depth measurements were determined. The MOSkin detector showed a reliable response when tested under Co-60 brachytherapy range of doses with an excellent linearity of R 2  = 0.9997 and acceptable reproducibility. A phantom verification study was also conducted to verify the differences between MOSkin responses and treatment planning (TPS) calculated doses. By taking into account several correction factors, deviations ranging between 0.01 and 0.4 Gy were found between MOSkin measured and TPS doses at measurement distance of 20-55 mm. The use of MOSkin as the dosimeter of choice for in vivo dosimetry under Co-60 brachytherapy condition is feasible., (Copyright © 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Objective: To determine and compare treatment outcomes between cobalt-60 (Co-60) and iridium-192 (Ir-192) high dose rate (HDR) brachytherapy in stage IB2-IIIB cervical cancer patients at Department of Radiology, Faculty of Medicine Vajira Hospital, Navamindrahiraj University., Methods: A retrospective cohort study of patients diagnosed with cervical cancer and treated with radiotherapy at the Department of Radiation Oncology, Faculty of Medicine Vajira Hospital between 2004 and 2014. Survival rate was analyzed by Kaplan-Meier method and were compared between groups with log-rank test. Multivariate analysis was performed using Cox proportional hazards model., Results: A total of 480 patients with cervical cancer and treated with radiotherapy were included, 274 patients for Ir-192 group and 206 patients for Co-60 group. The 2- and 5-year disease-free survival rate in Ir-192 group were 80.4% and 73.1% and in Co-60 group were 82.5% and 74.7%, respectively (p=0.365). Overall survival rates at 2 and 5 years were 89.4% and 77% of the Ir-192 group, and 91.6% and 81.9% in the Co-60 group, respectively (p=0.238). The complications were primarily grade 1 or 2. Grade 3 and 4 complications were found in 13 of 274 and 7 of 206 in Ir-192 and Co-60 groups, respectively (p=0.232). Grade and clinical stage of cancer significantly affected the survival outcome., Conclusion: Cervical cancer patients who were treated with HDR Co-60 brachytherapy were comparable in survival and toxicity outcomes of those with HDR Ir-192 brachytherapy. Co-60 source has lots of economic advantages over Ir-192 and hence suitable for low resource radiotherapy setting., Competing Interests: No potential conflict of interest relevant to this article was reported., (Copyright © 2018. Asian Society of Gynecologic Oncology, Korean Society of Gynecologic Oncology.)

The 0.35 T 60 Co MRIdian system (ViewRay Inc., Mountain View) has been in clinical use in our institution since May 2016. For quality assurance (QA) of dose delivery and end-to-end testing for this machine, a reliable dosimeter is required. However, it is possible that a magnetic field may cause perturbations to dosimetry measurements. For static magnetic fields, there is conflicting information in the literature concerning EBT film behaviour, while for real-time MR imaging such information is not available at all. The purpose of this study was to investigate the suitability of EBT3 GafChromic film for MRIdian QA, both with and without real-time MR imaging. EBT3 film sheets were irradiated in water using the MRIdian and a conventional linear accelerator (Linac) for reference. Dose calibration measurements were first performed up to 8 Gy for both machines. The MRIdian measurements were performed with and without real-time MR imaging. Second, film sheets were irradiated at seven different angles with respect to the B 0 -field. Optical density and dose values were analysed for the three colour channels. In both the film dose-response and B 0 -field orientation measurements, the mean dose values were within the 1% uncertainty range of prescribed dose values for the red and green channels, for both machines. There were no dose deviations detected between the MRIdian and Linac film measurements, nor for different B 0 -field orientations. In addition, the film dose-response measurements during real-time imaging were within 1.5% of the reference Linac measurements. EBT3 GafChromic film can be used for absolute dosimetry during real-time MR imaging independent of its orientation in the B 0 -field. This makes it a suitable dosimeter for patient-specific QA measurements and end-to-end testing of 0.35 T MRI-radiotherapy devices.

We describe the commissioning of the first dedicated commercial total body irradiation (TBI) unit in clinical operation. The Best Theratronics GammaBeam 500 is a Co-60 teletherapy unit with extended field size and imaging capabilities. Radiation safety, mechanical and imaging systems, and radiation output are characterized. Beam data collection, calibration, and external dosimetric validation are described. All radiation safety and mechanical tests satisfied relevant requirements and measured dose distributions meet recommendations of American Association of Physicists in Medicine (AAPM) Report #17. At a typical treatment distance, the dose rate in free space per unit source activity using the thick flattening filter is 1.53 × 10 -3 cGy*min -1 *Ci -1 . With a 14,000 Ci source, the resulting dose rate at the midplane of a typical patient is approximately 17 and 30 cGy/min using the thick and thin flattening filters, respectively, using the maximum source to couch distance. The maximum useful field size, defined by the 90% isodose line, at this location is 225 × 78 cm with field flatness within 5% over the central 178 × 73 cm. Measured output agreed with external validation within 0.5%. End-to-end testing was performed in a modified Rando phantom. In-house MATLAB software was developed to calculate patient-specific dose distributions using DOSXYZnrc, and fabricate custom 3D-printed forms for creating patient-specific lung blocks. End-to-end OSLD and diode measurements both with and without lung blocks agreed with Monte Carlo calculated doses to within 5% and in-phantom film measurements validated dose distribution uniformity. Custom lung block transmission measurements agree well with design criteria and provide clinically favorable dose distributions within the lungs. Block placement is easily facilitated using the flat panel imaging system with an exposure time of 0.01 min. In conclusion, a novel dedicated TBI unit has been commissioned and clinically implemented. Its mechanical, dosimetric, and imaging capabilities are suitable to provide state-of-the-art TBI for patients as large as 220 cm in height and 78 cm in width., (© 2018 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

Background: The quality of radiotherapy services in post-Soviet countries has not yet been studied following a formal methodology. The IAEA conducted a survey using two sets of validated radiation oncology quality indicators (ROIs)., Methods: Eleven post-Soviet countries were assessed. A coordinator was designated for each country and acted as the liaison between the country and the IAEA. The methodology was a one-time cross-sectional survey using a 58-question tool in Russian. The questionnaire was based on two validated sets of ROIs: for radiotherapy centres, the indicators proposed by Cionini et al., and for data at the country level, the Australasian ROIs., Results: The overall response ratio was 66.3%, but for the Russian Federation, it was 24%. Data were updated on radiotherapy infrastructure and equipment. 256 radiotherapy centres are operating 275 linear accelerators and 337 Cobalt-60 units. 61% of teletherapy machines are older than ten years. Analysis of ROIs revealed significant differences between these countries and radiotherapy practices in the West. Naming, task profile and education programmes of radiotherapy professionals are different than in the West., Conclusions: Most countries need modernization of their radiotherapy infrastructure coupled with adequate staffing numbers and updated education programmes focusing on evidence-based medicine, quality, and safety., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Purpose: Most women with cervical cancer in Sub-Saharan Africa present with locally advanced disease. These women require external beam radiation therapy and brachytherapy for curative treatment, but data on their outcomes remain sparse. We report data on treatment characteristics, follow-up, toxicity, and cancer outcomes in a large population of patients from the National Centre for Radiotherapy in Accra, Ghana., Methods and Materials: The charts of patients treated from 2006 to 2011 were reviewed. Patients treated without brachytherapy or with palliative intent were excluded. Staging computed tomography scans were not routinely performed. Cobalt 60 external beam radiation therapy was followed by 2 low-dose-rate brachytherapy insertions. Concurrent weekly cisplatin was recommended. Because many patients experienced delays from diagnosis to treatment, we calculated overall survival and locoregional recurrence from the date of first radiation therapy to the event date-or last follow-up when no event recurred-using the Kaplan-Meier (product-limit) method., Results: We included 250 patients with a median age at diagnosis of 55 years. The International Federation of Gynecology and Obstetrics stage was IIB or lower in 63% of patients. The median dose to point A was 83 Gy (range, 60-97.5 Gy). The median doses to the bladder and rectal points were 71 Gy and 65 Gy, respectively. Of the patients, 69% received ≥4 cycles of concurrent cisplatin. The median overall treatment time was 73 days. The median follow-up period was 2.4 years, with 3-year overall survival and locoregional recurrence rates of 86% and 19%, respectively. The most commonly reported late side effect was vaginal stenosis and shortening, occurring in 32% of patients. We also identified nearly 300 patients who were offered curative treatment but never returned to start treatment., Conclusions: We report promising outcomes in a population of women with cervical cancer treated with concurrent chemoradiation therapy and brachytherapy in Ghana. To our knowledge, this is the largest series of its kind, and it demonstrates what can be achieved with a well-established cancer program in Sub-Saharan Africa., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Current practices in radiation therapy required high doses of radiation to be delivered with increased accuracy. Treatment planning task is exercised till an optimum dose distribution is achieved. The present reported work was performed to compare the various aspects of the cobalt-60 radiation beam therapy with fixed source-surface distance 70cm incident normally. This study was conducted in May 2012 at the Department of Radiation Physics of MD Anderson Cancer Centre, University of Texas, Houston, United States. Radiation doses were calculated in a solid phantom as well as in water phantom at different square field sizes and depths. It was noted that the rate of absorbed dose increased with the increase in the field size and decreased with the increase in depths. The rate of absorbed dose was found to be directly proportional to the increase in the square field size and inversely proportional to the increase in depth. Moreover, the solid phantom demonstrated more absorbed doses as compared to the water phantom.

Purpose: To investigate the feasibility of using the ratio of dose-area product at 20 cm and 10 cm water depths (DAPR 20,10 ) as a beam quality specifier for radiotherapy photon beams with field diameter below 2 cm., Methods: Dose-area product was determined as the integral of absorbed dose to water (D w ) over a surface larger than the beam size. 6 MV and 10 MV photon beams with field diameters from 0.75 cm to 2 cm were considered. Monte Carlo (MC) simulations were performed to calculate energy-dependent dosimetric parameters and to study the DAPR 20,10 properties. Aspects relevant to DAPR 20,10 measurement were explored using large-area plane-parallel ionization chambers with different diameters., Results: DAPR 20,10 was nearly independent of field size in line with the small differences among the corresponding mean beam energies. Both MC and experimental results showed a dependence of DAPR 20,10 on the measurement setup and the surface over which D w is integrated. For a given setup, DAPR 20,10 values obtained using ionization chambers with different air-cavity diameters agreed with one another within 0.4%, after the application of MC correction factors accounting for effects due to the chamber size. DAPR 20,10 differences among the small field sizes were within 1% and sensitivity to the beam energy resulted similar to that of established beam quality specifiers based on the point measurement of D w ., Conclusions: For a specific measurement setup and integration area, DAPR 20,10 proved suitable to specify the beam quality of small photon beams for the selection of energy-dependent dosimetric parameters., (Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

Introduction: To evaluate the intra-/interobserver variability of gross target volumes between delineation based on magnetic resonance imaging and computed tomography in patients simulated for stereotactic body radiotherapy for primary lung cancer and lung metastasis., Materials and Methods: Twenty-five patients (27 lesions) who underwent computed tomography and magnetic resonance simulation with the MR- 60 Co system (ViewRay) were included in the study. Gross target volumes were delineated on the magnetic resonance imaging (GTV MR ) and computed tomography (GTV CT ) images by 2 radiation oncologists (RO1 and RO2). Volumes of all contours were measured. Levels of intraobserver (GTV MR &#95;RO vs GTV CT &#95;RO) and interobserver (GTV MR &#95;RO1 vs GTV MR &#95;RO2; GTV CT &#95;RO1 vs GTV CT &#95;RO2) agreement were evaluated using the generalized κ statistics and the paired t test., Results: No significant volumetric difference was observed between all 4 comparisons (GTV MR &#95;RO1 vs GTV CT &#95;RO1, GTV MR &#95;RO2 vs GTV CT &#95;RO2, GTV MR &#95;RO1 vs GTV MR &#95;RO2, and GTV CT &#95;RO1 vs GTV CT &#95;RO2; P > .05), with mean volumes of GTVs ranging 5 to 6 cm 3 . The levels of agreement between those 4 comparisons were all substantial with mean κ values of 0.64, 0.66, 0.74, and 0.63, respectively. However, the interobserver agreement level was significantly higher for GTV CT compared to GTV MR ( P <.001). The mean κ values significantly increased in all 4 comparisons for tumors >5 cm 3 compared to tumors ≤5 cm 3 (all P < .05)., Conclusion: No significant differences in volumes between magnetic resonance- and computed tomograpghy-based Gross target volumes were found among 2 ROs. Magnetic resonance-based GTV delineation for lung stereotactic body radiotherapy also demonstrated acceptable interobserver agreement. Tumors >5 cm 3 show higher intra-/interobserver agreement compared to tumors <5 cm 3 . More experience should be accumulated to reduce variability in magnetic resonance-based Gross target volumes delineation in lung stereotactic body radiotherapy.

This study aimed to evaluate dose uniformity for 192 Ir and 60 Co stepping sources. High dose rate 192 Ir and 60 Co stepping sources were simulated by the MCNPX Monte Carlo code. To investigate dose uniformity, treatment lengths of 30, 50, 100, and 150 mm with stepping distances of 3, 5, 7, and 10 mm were considered. Finally, dose uniformity for the 192 Ir and 60 Co stepping sources with increasing distances from the source were assessed at these treatment lengths and steps. The findings showed that the dose distribution was non-uniform for regions in close vicinity of the source, especially in the high source steps, but for most points at distances >10 mm from the center of the source, the dose distribution was uniform. For most points, the dose uniformity increased with reduction of the source steps and increments of the transverse distance from the source. The dose non-uniformity was similar for most of the corresponding points of 60 Co and 192 Ir sources with the same treatment lengths and source steps, except at the distance of 150 mm. When using stepping technique for the treatment of tumors, more attention should be focused on treatment planning, especially with higher stepping distances and lower transverse distances from the source.

Purpose: To evaluate plan quality of a novel MRI-compatible direction modulated brachytherapy (DMBT) tandem applicator using 192 Ir, 60 Co, and 169 Yb HDR brachytherapy sources, for various cervical cancer high-risk clinical target volumes (CTV HR )., Materials and Methods: The novel DMBT tandem applicator has six peripheral grooves of 1.3-mm diameter along a 5.4-mm thick nonmagnetic tungsten alloy rod. Monte Carlo (MC) simulations were used to benchmark the dosimetric parameters of the 192 Ir, 60 Co, and 169 Yb HDR sources in a water phantom against the literature data. 45 clinical cases that were treated using conventional tandem-and-ring applicators with 192 Ir source ( 192 Ir-T&R) were selected consecutively from intErnational MRI-guided BRAchytherapy in CErvical cancer (EMBRACE) trial. Then, for each clinical case, 3D dose distribution of each source inside the DMBT and conventional applicators were calculated and imported onto an in-house developed inverse planning optimization code to generate optimal plans. All plans generated by the DMBT tandem-and-ring (DMBT T&R) from all three sources were compared to the respective 192 Ir-T&R plans. For consistency, all plans were normalized to the same CTV HR D90 achieved in clinical plans. The D 2 cm3 for organs at risk (OAR) such as bladder, rectum, and sigmoid, and D90, D98, D10, V100, and V200 for CTV HR were calculated., Results: In general, plan quality significantly improved when a conventional tandem (Con.T) is replaced with the DMBT tandem. The target coverage metrics were similar across 192 Ir-T&R and DMBT T&R plans with all three sources (P > 0.093). 60 Co-DMBT T&R generated greater hot spots and less dose homogeneity in the target volumes compared with the 192 Ir- and 169 Yb-DMBT T&R plans. Mean OAR doses in the DMBT T&R plans were significantly smaller (P < 0.0084) than the 192 Ir-T&R plans. Mean bladder D 2 cm3 was reduced by 4.07%, 4.15%, and 5.13%, for the 192 Ir-, 60 Co-, and 169 Yb-DMBT T&R plans respectively. Mean rectum (sigmoid) D 2 cm3 was reduced by 3.17% (3.63%), 2.57% (3.96%), and 4.65% (4.34%) for the 192 Ir-, 60 Co-, and 169 Yb-DMBT T&R plans respectively. The DMBT T&R plans with the 169 Yb source generally resulted in the greatest OAR sparing when the CTV HR were larger and irregular in shape, while for smaller and regularly shaped CTV HR (<30 cm 3 ), OAR sparing between the sources were comparable., Conclusions: The DMBT tandem provides a promising alternative to the Con.T design with significant improvement in the plan quality for various target volumes. The DMBT T&R plans generated with the three sources of varying energies generated superior plans compared to the conventional T&R applicators. Plans generated with the 169 Yb-DMBT T&R produced best results for larger and irregularly shaped CTV HR in terms of OAR sparing. Thus, this study suggests that the combination of the DMBT tandem applicator with varying energy sources can work synergistically to generate improved plans for cervical cancer brachytherapy., (© 2017 American Association of Physicists in Medicine.)

Introduction: Endovaginal brachytherapy treatment dosimetry differences were studied using Ir-192 or Co-60 sources for postoperative endometrial cancer., Materials and Methods: A prospective descriptive study was conducted. Thirty-six dosimetry plans of different patients were studied (15 by Ir-192 and 21 by Co-60). Variables studied included D2cc Rectum, D2cc Bladder, D2cc Sigmoid, dose percentage at point 0 (applicator surface on the top of the cylinder) and dose percentage at point 1 (5 mm deep on the top of the cylinder). A comparative analysis was performed of the values obtained from each variable between Ir-192 and Co-60 treatments. We compared average of each variables between Iridium and Cobalt by T Student for independent samples (SPSS 22)., Results: There were no significant differences on using Ir-192 or Co-60 by variables, except for dose percentage at point 1 in which we detected significant differences (Table 1). Table 1 The results Variables Sources Iridium 192 Cobalt 60 D2cc Rectum (mean dose) [rank] 6.01 Gy [3.99-7.90] 5.28 Gy [3.87-6,34] D2cc Bladder (mean dose) [rank] 5.82 Gy [4.20-8.38] 5.05 Gy [2.23-6.95] D2cc Sigmoid (mean dose) [rank] 4.43 Gy [1.66-6.67] 2.33 Gy [0.60-4.28] Dose percentage at point 0 a (mean) [rank] 210.74% [120.90-234.90] 204.75% [177.10-223] Dose percentage at point 1 b (mean) [rank] 93.49% [87.30-100.60] 100.11% [96.70-102] a Point 0: point to the applicator surface b Point 1: point to 5 mm applicator surface DISCUSSION: Brachytherapy treatment dosimetry plans are similar using Ir-192 or Co-60, except dose percentage at point 1. In the scientific literature, some differences exist and there are some advantages in using cobalt.

Purpose: Monitoring tumor response during the course of treatment and adaptively modifying treatment plan based on tumor biological feedback may represent a new paradigm for radiotherapy. Diffusion MRI has shown great promises in assessing and predicting tumor response to radiotherapy. However, the conventional diffusion-weighted single-shot echo-planar-imaging (DW-ssEPI) technique suffers from limited resolution, severe distortion, and possibly inaccurate ADC at low field strength. The purpose of this work was to develop a reliable, accurate and distortion-free diffusion MRI technique that is practicable for longitudinal tumor response evaluation and adaptive radiotherapy on a 0.35 T MRI-guided radiotherapy system., Methods: A diffusion-prepared turbo spin echo readout (DP-TSE) sequence was developed and compared with the conventional diffusion-weighted single-shot echo-planar-imaging sequence on a 0.35 T MRI-guided radiotherapy system (ViewRay). A spatial integrity phantom was used to quantitate and compare the geometric accuracy of the two diffusion sequences for three orthogonal orientations. The apparent diffusion coefficient (ADC) accuracy was evaluated on a diffusion phantom under both 0 °C and room temperature to cover a diffusivity range between 0.40 × 10 -3 and 2.10 × 10 -3 mm 2 /s. Ten room temperature measurements repeated on five different days were conducted to assess the ADC reproducibility of DP-TSE. Two glioblastoma (GBM) and six sarcoma patients were included to examine the in vivo feasibility. The target registration error (TRE) was calculated to quantitate the geometric accuracy where structural CT or MR images were co-registered to the diffusion images as references. ADC maps from DP-TSE and DW-ssEPI were calculated and compared. A tube phantom was placed next to patients not treated on ViewRay, and ADCs of this reference tube were also compared., Results: The proposed DP-TSE passed the spatial integrity test (< 1 mm within 100 mm radius and < 2 mm within 175 mm radius) under the three orthogonal orientations. The detected errors were 0.474 ± 0.355 mm, 0.475 ± 0.287 mm, and 0.546 ± 0.336 mm in the axial, coronal, and sagittal plane. DW-ssEPI, however, failed the tests due to severe distortion and low signal intensity. Noise correction must be performed for the DW-ssEPI to avoid ADC quantitation errors, whereas it is optional for DP-TSE. At 0 °C, the two sequences provided accurate quantitation with < 3% variation with the reference. In the room temperature study, discrepancies between ADCs from DP-TSE and the reference were within 4%, but could be as high as 8% for DW-ssEPI after the noise correction. Excellent ADC reproducibility with a coefficient of variation < 5% was observed among the 10 measurements of DP-TSE, indicating desirable robustness for ADC-based tumor response assessment. In vivo TRE in DP-TSE was less than 1.6 mm overall, whereas it could be greater than 12 mm in DW-ssEPI. For GBM patients, the CSF and brain tissue ADCs from DP-TSE were within the ranges found in literature. ADC differences between the two techniques were within 8% among the six sarcoma patients. For the reference tube that had a relatively low diffusivity, the two diffusion sequences provided matched measurements., Conclusion: A diffusion technique with excellent geometric fidelity, accurate, and reproducible ADC measurement was demonstrated for longitudinal tumor response assessment using a low-field MRI-guided radiotherapy system., (© 2017 American Association of Physicists in Medicine.)

Historical radiotherapy treatment plans lack 3D images sets required for estimating mean organ doses to patients. Alternatively, Monte Carlo-based models of radiotherapy devices coupled with whole-body computational phantoms can permit estimates of historical in-field and out-of-field organ doses as needed for studies associating radiation exposure and late tissue toxicities. In recreating historical patient treatments with 60 Co based systems, the major components to be modeled include the source capsule, surrounding shielding layers, collimators (both fixed and adjustable), and trimmers as needed to vary field size. In this study, a computational model and experimental validation of the Theratron T-1000 are presented. Model validation is based upon in-field commissioning data collected at the University of Florida, published out-of-field data from the British Journal of Radiology (BJR) Supplement 25, and out-of-field measurements performed at the University of Wisconsin's Accredited Dosimetry Calibration Laboratory (UWADCL). The computational model of the Theratron T-1000 agrees with central axis percentage depth dose data to within 2% for 6  ×  6 to 30  ×  30 cm 2 fields. Out-of-field doses were found to vary between 0.6% to 2.4% of central axis dose at 10 cm from field edge and 0.42% to 0.97% of central axis dose at 20 cm from the field edge, all at 5 cm depth. Absolute and relative differences between computed and measured out-of-field doses varied between  ±2.5% and  ±100%, respectively, at distances up to 60 cm from the central axis. The source-term model was subsequently combined with patient-morphometry matched computational hybrid phantoms as a method for estimating in-field and out-of-field organ doses for patients treated for Hodgkin's Lymphoma. By changing field size and position, and adding patient-specific field shaping blocks, more complex historical treatment set-ups can be to recreated, particularly those for which 2D or 3D image sets are unavailable.

Normally, differentiated thyroid cancer (DTC) tends to be biologically indolent, highly curable and has an excellent prognosis. However, the treatment may fail when the cancer has lost radioiodine avidity. The present study was carried out in order to evaluate the cytotoxic and genotoxic effects of 131 I and 60 Co and radioiodine uptake in WRO cells, derived from DTC, harboring the BRAF V600E mutation. WRO cells showed a relatively slow cell cycle of 96.3 h with an unstable karyotype containing various double minutes. The genotoxicity assay (micronucleus test) showed a relative high radioresistance to 131 I (0.07-3.70 MBq/mL), independent of treatment with recombinant human thyroid-stimulating hormone (rhTSH). For the cytotoxicity assay, WRO cells were also relatively resistant to 60 Co (range: 0.2-8.3 Gy), but with a gradual decrease of viability as a function of time for higher doses (20 and 40 Gy, starting from the fifth to sixth day). For internal irradiation with 131 I, WRO cells showed a decline in viability at radioactive concentration higher than 1.85 MBq/mL; this was even more effective at 3.70 MBq/mL, but only when preceded by rhTSH, in coincidence with the highest level of 131 I uptake. These data show promising results, since the loss of the ability of thyroid cells to concentrate radioiodine is considered to be one of the main factors responsible for the failure of 131 I therapy in patients with DTC. The use of tumor-derived cell lines as a model for in vivo tumor requires, however, further investigations and deep evaluation of the corresponding in vivo effects. Environ. Mol. Mutagen. 58:451-461, 2017. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

Purpose: Magnetic resonance imaging-guided radiation therapy has entered clinical practice at several major treatment centers. Treatment of early-stage non-small cell lung cancer with stereotactic body radiation therapy is one potential application of this modality, as some form of respiratory motion management is important to address. We hypothesize that magnetic resonance imaging-guided tri-cobalt-60 radiation therapy can be used to generate clinically acceptable stereotactic body radiation therapy treatment plans. Here, we report on a dosimetric comparison between magnetic resonance imaging-guided radiation therapy plans and internal target volume-based plans utilizing volumetric-modulated arc therapy., Materials and Methods: Ten patients with early-stage non-small cell lung cancer who underwent radiation therapy planning and treatment were studied. Following 4-dimensional computed tomography, patient images were used to generate clinically deliverable plans. For volumetric-modulated arc therapy plans, the planning tumor volume was defined as an internal target volume + 0.5 cm. For magnetic resonance imaging-guided plans, a single mid-inspiratory cycle was used to define a gross tumor volume, then expanded 0.3 cm to the planning tumor volume. Treatment plan parameters were compared., Results: Planning tumor volumes trended larger for volumetric-modulated arc therapy-based plans, with a mean planning tumor volume of 47.4 mL versus 24.8 mL for magnetic resonance imaging-guided plans ( P = .08). Clinically acceptable plans were achievable via both methods, with bilateral lung V20, 3.9% versus 4.8% ( P = .62). The volume of chest wall receiving greater than 30 Gy was also similar, 22.1 versus 19.8 mL ( P = .78), as were all other parameters commonly used for lung stereotactic body radiation therapy. The ratio of the 50% isodose volume to planning tumor volume was lower in volumetric-modulated arc therapy plans, 4.19 versus 10.0 ( P < .001). Heterogeneity index was comparable between plans, 1.25 versus 1.25 ( P = .98)., Conclusion: Magnetic resonance imaging-guided tri-cobalt-60 radiation therapy is capable of delivering lung high-quality stereotactic body radiation therapy plans that are clinically acceptable as compared to volumetric-modulated arc therapy-based plans. Real-time magnetic resonance imaging provides the unique capacity to directly observe tumor motion during treatment for purposes of motion management.

Medical linear accelerators (linacs) and cobalt-60 machines are both mature technologies for external beam radiotherapy. A comparison is made between these two technologies in terms of infrastructure and maintenance, dosimetry, shielding requirements, staffing, costs, security, patient throughput and clinical use. Infrastructure and maintenance are more demanding for linacs due to the complex electric componentry. In dosimetry, a higher beam energy, modulated dose rate and smaller focal spot size mean that it is easier to create an optimised treatment with a linac for conformal dose coverage of the tumour while sparing healthy organs at risk. In shielding, the requirements for a concrete bunker are similar for cobalt-60 machines and linacs but extra shielding and protection from neutrons are required for linacs. Staffing levels can be higher for linacs and more staff training is required for linacs. Life cycle costs are higher for linacs, especially multi-energy linacs. Security is more complex for cobalt-60 machines because of the high activity radioactive source. Patient throughput can be affected by source decay for cobalt-60 machines but poor maintenance and breakdowns can severely affect patient throughput for linacs. In clinical use, more complex treatment techniques are easier to achieve with linacs, and the availability of electron beams on high-energy linacs can be useful for certain treatments. In summary, there is no simple answer to the question of the choice of either cobalt-60 machines or linacs for radiotherapy in low- and middle-income countries. In fact a radiotherapy department with a combination of technologies, including orthovoltage X-ray units, may be an option. Local needs, conditions and resources will have to be factored into any decision on technology taking into account the characteristics of both forms of teletherapy, with the primary goal being the sustainability of the radiotherapy service over the useful lifetime of the equipment., (Copyright © 2016 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.)

OBJECTIVE Functional Gamma Knife radiosurgery (GKRS) procedures have been increasingly used for treating patients with tremor, trigeminal neuralgia (TN), and refractory obsessive-compulsive disorder. Although its rates of toxicity are low, GKRS has been associated with some, if low, risks for serious sequelae, including hemiparesis and even death. Anecdotal reports have suggested that even with a standardized prescription dose, rates of functional GKRS toxicity increase after replacement of an old cobalt-60 source with a new source. Dose rate changes over the course of the useful lifespan of cobalt-60 are not routinely considered in the study of patients treated with functional GKRS, but these changes may be associated with significant variation in the biologically effective dose (BED) delivered to neural tissue. METHODS The authors constructed a linear-quadratic model of BED in functional GKRS with a dose-protraction factor to correct for intrafraction DNA-damage repair and used standard single-fraction doses for trigeminal nerve ablation for TN (85 Gy), thalamotomy for tremor (130 Gy), and capsulotomy for obsessive-compulsive disorder (180 Gy). Dose rate and treatment time for functional GKRS involving 4-mm collimators were derived from calibrations in the authors' department and from the cobalt-60 decay rate. Biologically plausible values for the ratio for radiosensitivity to fraction size (α/β) and double-strand break (DSB) DNA repair halftimes (τ) were estimated from published experimental data. The biphasic characteristics of DSB repair in normal tissue were accounted for in deriving an effective τ 1 halftime (fast repair) and τ 2 halftime (slow repair). A sensitivity analysis was performed with a range of plausible parameter values. RESULTS After replacement of the cobalt-60 source, the functional GKRS dose rate rose from 1.48 to 2.99 Gy/min, treatment time fell, and estimated BED increased. Assuming the most biologically plausible parameters, source replacement resulted in an immediate relative BED increase of 11.7% for GKRS-based TN management with 85 Gy, 15.6% for thalamotomy with 130 Gy, and 18.6% for capsulotomy with 180 Gy. Over the course of the 63-month lifespan of the cobalt-60 source, BED decreased annually by 2.2% for TN management, 3.0% for thalamotomy, and 3.5% for capsulotomy. CONCLUSIONS Use of a new cobalt-60 source after replacement of an old source substantially increases the predicted BED for functional GKRS treatments for the same physical dose prescription. Source age, dose rate, and treatment time should be considered in the study of outcomes after high-dose functional GKRS treatments. Animal and clinical studies are needed to determine how this potential change in BED contributes to GKRS toxicity and whether technical adjustments should be made to reduce dose rates or prescription doses with newer cobalt-60 sources.

Purpose: Magnetic resonance imaging (MRI)-guided Co-60 provides daily and intrafractional MRI soft tissue imaging for improved target and critical organ tracking. To increase delivery efficiency, the system uses three Co-60 sources at 120° apart, allowing up to 600 cGy combined dose rate at isocenter. Despite the potential tripling in output, creating a delivery plan that uses all three sources is considerably unintuitive. Here, the authors computerize the triplet orientation optimization using column generation, an approach that was demonstrated effective in integrated beam orientation and fluence optimization for noncoplanar therapies. To achieve a better plan quality without increasing the treatment time, the authors then solve a fluence map optimization (FMO) problem while regularizing the fluence maps to reduce the number of deliverable MLC segments., Methods: Three patients-one prostate, one lung, and one head and neck boost plan (H&N Boost )-were evaluated in this study. For each patient, the beamlet doses were calculated using Monte Carlo, under a 0.35 T magnetic field, for 180 equally spaced coplanar beams grouped into 60 triplets. The beamlet size is 1.05 × 0.5 cm determined by the MLC leaf thickness and step size. The triplets were selected using the column generation algorithm. The FMO problem was formulated using an L2-norm dose fidelity term and an L1-norm anisotropic total variation regularization term, which allows controlling the number of MLC segments, and hence the treatment time, with minimal degradation to the dose. The authors' Fluence Regularization and Optimized Selection of Triplets (FROST) plans were compared against the clinical treatment plans (CLNs) produced by an experienced dosimetrist. PTV homogeneity, max dose, mean dose, D95, D98, and D99 were evaluated. OAR max and mean doses, as well as R50, defined as the ratio of the 50% isodose volume over the planning target volume were investigated., Results: The mean PTV D95, D98, and D99 differ by +0.04%, +0.07%, and +0.25% of the prescription dose between planning methods. The mean PTV homogeneity was virtually same with values at 0.8788 (FROST) and 0.8812 (CLN). R50 decreased by 0.67 comparing FROST to CLN. On average, FROST reduced D max and D mean of OARs by 7.30% and 6.08% of the prescription dose, respectively. The manual CLN planning processes required numerous trial and error runs. The FROST plans on the other hand required minimal human intervention., Conclusions: Efficient delivery of MRI-guided Co-60 therapy needs the output of multiple sources yet suffers from unintuitive and laborious manual beam selection processes. Computerized triplet orientation optimization improves both planning efficiency and plan dosimetry. The novel fluence map regularization provides additional controls over the number of MLC segments and treatment time.

Purpose: Magnetic resonance imaging (MRI) guidance in radiation therapy brings real-time imaging and adaptive planning into the treatment vault where it can account for interfraction and intrafraction movement of soft tissue. The only commercially available MRI-guided radiation therapy device is a three-head (60)Co and MRI system with an integrated treatment planning system (TPS). Couch attenuation of the beam of up to 20% is well modeled in the TPS. Variations in the patient's day-to-day position introduce discrepancies in the actual couch attenuation as modeled in the treatment plan. For this reason, the authors' institution avoids plans with beams that pass through or near the couch edges. This study investigates the effects of differential beam attenuation by the couch due to couch shifts in order to determine whether couch edge avoidance restrictions can be lifted. Couch shifts were simulated using a Monte Carlo treatment planning system and ion chamber measurements performed for validation., Methods: A total of 27 plans from 23 patients were investigated. Couch shifts of 1 and 2 cm were introduced in combinations of lateral and vertical directions to simulate patient position variations giving 16 shifted plans per reference plan. The 1 and 2 cm shifts were based on shifts recorded in 320 treatment fractions., Results: Following TG176 recommendations for measurement methods, couch attenuation measurements agreed with TPS modeled attenuation to within 2.1%. Planning target volume D95 changed less than 1% for 1 and 2 cm couch shifts in only the x-direction and less than 3% for all directions., Conclusions: Dosimetry of all plans tested was robust to couch shifts up to ±2 cm. In general, couch shifts resulted in clinically insignificant dosimetric deviations. It is conceivable that in certain cases with large systematic couch shifts and plans that are particularly sensitive to shifts, dosimetric changes might rise to a clinically significant level.

A new method for the design of stepless beam modulators for proton therapy is described and verified. Simulations of the classic designs are compared against the stepless method for various modulation widths which are clinically applicable in proton eye therapy. Three modulator wheels were printed using a Stratasys Objet30 3D printer. The resulting depth dose distributions showed improved uniformity over the classic stepped designs. Simulated results imply a possible improvement in distal penumbra width; however, more accurate measurements are needed to fully verify this effect. Lastly, simulations were done to model bio-equivalence to Co-60 cell kill. A wheel was successfully designed to flatten this metric.

This paper presents a new approach towards the quality assurance of external beam plans using in-house-developed DICOM import and export software in a clinical setup. The new approach is different from what is currently used in most clinics, viz., only MU and point dose are verified. The DICOM-RT software generates ASCII files to import/export structure sets, treatment beam data, and dose-volume histo-grams (DVH) from one treatment planning system (TPS) to the other. An efficient and reliable 3D planning system, ROPS, was used for verifying the accuracy of treatment plans and treatment plan parameters. With the use of this new approach, treatment plans planned using Varian Eclipse planning system were exported to ROPS planning system. Important treatment and dosimetrical data, such as the beam setup accuracy, target dose coverage, and dose to critical structures, were also quantitatively verified using DVH comparisons. Two external beam plans with diverse photon energies were selected to test the new approach. The satisfactory results show that the new approach is feasible, easy to use, and can be used as an adjunct test for patient treatment quality check.