Search

Purpose Flattening filter free (FFF) beams are increasingly being considered for stereotactic radiotherapy (SRT). For the first time, the performance of a monolithic silicon array detector under 6 and 10 MV FFF beams was evaluated. The dosimeter, named “Octa” and designed by the Centre for Medical Radiation Physics (CMRP), was tested also under flattened beams for comparison. Methods Output factors (OFs), percentage depth-dose (PDD), dose profiles (DPs) and dose per pulse (DPP) dependence were investigated. Results were benchmarked against commercially available detectors for small field dosimetry. Results The dosimeter was shown to be a ‘correction-free’ silicon array detector for OFs and PDD measurements for all the beam qualities investigated. Measured OFs were accurate within 3% and PDD values within 2% compared against the benchmarks. Cross-plane, in-plane and diagonal DPs were measured simultaneously with high spatial resolution (0.3 mm) and real time read-out. A DPP dependence (24% at 0.021 mGy/pulse relative to 0.278 mGy/pulse) was found and could be easily corrected for in the case of machine specific quality assurance applications. Conclusions Results were consistent with those for monolithic silicon array detectors designed by the CMRP and previously characterized under flattened beams only, supporting the robustness of this technology for relative dosimetry for a wide range of beam qualities and dose per pulses. In contrast to its predecessors, the design of the Octa offers an exhaustive high-resolution 2D dose map characterization, making it a unique real-time radiation detector for small field dosimetry for field sizes up to 3 cm side. [ABSTRACT FROM AUTHOR]

Purpose: To report on significant dose enhancement effects caused by magnetic fields aligned parallel to 6 MV photon beam radiotherapy of small lung tumors. Findings are applicable to future inline MRI-guided radiotherapy systems. Methods: A total of eight clinical lung tumor cases were recalculated using Monte Carlo methods, and external magnetic fields of 0.5, 1.0, and 3 T were included to observe the impact on dose to the planning target volume (PTV) and gross tumor volume (GTV). Three plans were 6 MV 3D-CRT plans while 6 were 6 MV IMRT. The GTV's ranged from 0.8 to 16 cm³, while the PTV's ranged from 1 to 59 cm3. In addition, the dose changes in a 30 cm diameter cylindrical water phantom were investigated for small beams. The central 20 cm of this phantom contained either water or lung density insert. Results: For single beams, an inline magnetic field of 1 T has a small impact in lung dose distributions by reducing the lateral scatter of secondary electrons, resulting in a small dose increase along the beam. Superposition of multiple small beams leads to significant dose enhancements. Clinically, this process occurs in the lung tissue typically surrounding the GTV, resulting in increases to the D98% (PTV). Two isolated tumors with very small PTVs (3 and 6 cm³) showed increases in D98% of 23% and 22%. Larger PTVs of 13, 26, and 59 cm³ had increases of 9%, 6%, and 4%, describing a natural fall-off in enhancement with increasing PTV size. However, three PTVs bounded to the lung wall showed no significant increase, due to lack of dose enhancement in the denser PTV volume. In general, at 0.5 T, the GTV mean dose enhancement is around 60% lower than that at 1 T, while at 3 T, it is 5%-60% higher than 1 T. Conclusions: Monte Carlo methods have described significant and predictable dose enhancement effects in small lung tumor plans for 6 MV radiotherapy when an external inline magnetic field is included. Results of this study indicate that future clinical inline MRI-guided radiotherapy systems will be able to deliver a dosimetrically superior treatment to small (PTV < 15 cm³), isolated lung tumors over non-MRI-Linac systems. This increased efficacy coincides with the reimbursement in the United States of lung CT screening and the likely rapid growth in the number of patients with small lung tumors to be treated with radiotherapy. [ABSTRACT FROM AUTHOR]

Integral dose has been useful in investigations into the incidence of second primary malignancies in radiotherapy patients. This note outlines an approach to calculation of integral dose for a group of prostate patients using only data exported from a commercial record and verify system. Even though it was necessary to make some assumptions about patient anatomy, comparison with integral dose calculated from data exported from the planning system showed good agreement. [ABSTRACT FROM AUTHOR]

Late pulmonary toxicity, including bronchial stenosis and fatal hemoptysis, can manifest in up to 35% of patients with central lung tumors treated using stereotactic ablative radiotherapy (SABR). Reliable tolerance doses for central airways are currently lacking. We postulated that objective and earlier identification of airway toxicity may be possible with an automated scoring method using quantitative CT and artificial intelligence (AI)-based airway segmentation to quantify post-SABR bronchial stenosis or occlusion. Patients treated with central lung SABR at two institutions were selected in an Ethics-approved study to define an internal reference dataset and an external validation dataset. Patients were eligible if they had pre- and post-SABR CT scans with ≤1mm slice thickness. Automated scoring was initiated by AI-based airway auto-segmentation using MEDPSeg, an end-to-end deep learning-based model (http://arxiv.org/abs/2312.02365). Next, the Vascular Modeling Toolkit in 3D Slicer (https://www.slicer.org) was used to extract a centerline curve through the auto-segmented airway lumen, and cross-sectional measurements were computed along each bronchial segment for all CT scans. Stenosis was significant if (100∗ (median radius-minimum radius) ÷median radius) = ≥50%. For the internal dataset, airways were evaluated by both visual assessment and automated scoring. Stenosis detected only by automated scoring were jointly reviewed by two investigators to reach consensus. Only the automated method was applied to the external dataset. A total of 26 and 33 patients were studied in the internal and external dataset, respectively. Visual scoring identified stenosis or occlusion in 8 patients from the internal set (31%), most frequently seen in the segmental bronchi. After airway auto-segmentation, minor manual edits were needed in 9% of patients. Time for segmenting a single scan averaged 83sec (range 73-136). Repeat measurements of airway diameters in the contralateral unirradiated lung revealed average relative differences (standard deviations) of 4.7% (± 6.3%), 5.2% (± 9.9%), and 4.9% (± 15.5%) respectively, for the main, lobar, and segmental bronchi. Automated scoring nearly doubled the detected cases of airway changes (n = 15, 58%), and allowed for earlier detection in 5/8 patients who had also visually scored changes, by a mean of 4 months. Estimated rates of airway damage were 48% and 66% at 1- and 2-years, respectively, for the internal set. The automated detection rate for airway damage was 52% in the external set, with 1- and 2-year risks of 56% and 61%, respectively. An AI-based automated scoring method detected more bronchial stenosis and/or occlusion after central lung SABR and did so at earlier time-points. Detection of early airway changes using this technique can allow for more reliable airway tolerance doses. [ABSTRACT FROM AUTHOR]

In response to the clinical need for a dosimetry system with both high resolution and minimal angular dependence, this study demonstrates the utility of Gafchromic EBT2 radiochromic dosimetry film for the quality assurance of micro-collimated IMRT, RapidArc and TomoTherapy treatments. Firstly, preliminary measurements indicated that the dose response of EBT2 film does not appreciably vary with either the angle of incidence of the radiation beam or the depth in water at which the film is placed. Secondly, prostate treatment plans designed for delivery using static-beam IMRT (collimated using the BrainLab m3 microMLC), RapidArc and TomoTherapy were investigated by comparing dose planes obtained from treatment planning calculations with EBT2 film measurements. For all treatment plans, the proportion of dose points agreeing with the film measurements to within γ (3%,3 mm) was found to be above 95%, with all points agreeing within 5%. The film images provided sufficient information to verify that the treatments could be delivered with an acceptable level of accuracy, while also providing additional information on low-level dose variations that were not predicted by the treatment planning systems. This information included: the location and extent of dose from inter-leaf leakage (in the RapidArc plan) and helical field junctioning (in the TomoTherapy plan), as well as the existence of small regions where the treatment planning system under-predicted the dose from very small treatment segments (in the micro-collimated IMRT plan). [ABSTRACT FROM AUTHOR]

Purpose: Helical tomotherapy is a complex delivery technique, integrating CT image guidance and intensity modulated radiotherapy in a single system. The integration of the CT detector ring on the gantry not only allows patient position verification but is also often used to perform various QA procedures. This convenience lacks the rigor of a machine-independent QA process. Methods: In this article, a Si strip detector, known as the Dose Magnifying Glass (DMG), was used to perform machine-independent QA measurements of the multileaf collimator alignment, leaf open time threshold, and leaf fluence output factor (LFOF). Results: The DMG measurements showed good agreements with EDR2 film for the MLC alignment test while the CT detector agrees well with DMG measurements for leaf open time threshold and LFOF measurements. The leaf open time threshold was found to be approximately 20 ms. The LFOF measured with the DMG agreed within error with the CT detector measured LFOF. Conclusions: The DMG with its 0.2 mm spatial resolution coupled to TERA ASIC allowed real-time high temporal resolution measurements of the tomotherapy leaf movement. In conclusion, DMG was shown to be a suitable tool for machine-independent QA of a tomotherapy unit. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations of the energy response of a conventionally packaged single metal-oxide field effect transistors (MOSFET) detector were performed with the goal of improving MOSFET energy dependence for personal accident or military dosimetry. The MOSFET detector packaging was optimised. Two different 'drop-in' design packages for a single MOSFET detector were modelled and optimised using the GEANT4 Monte Carlo toolkit. Absorbed photon dose simulations of the MOSFET dosemeter placed in free-air response, corresponding to the absorbed doses at depths of 0.07 mm (Dw(0.07)) and 10 mm (Dw(10)) in a water equivalent phantom of size 30 x 30 x 30 cm³ for photon energies of 0.015-2 MeV were performed. Energy dependence was reduced to within +60 % for photon energies 0.06-2 MeV for both Dw(0.07) and Dw(10). Variations in the response for photon energies of 15-60 keV were 200 and 330 % for Dw(0.07) and Dw(10), respectively. The obtained energy dependence was reduced compared with that for conventionally packaged MOSFET detectors, which usually exhibit a 500-700 % over-response when used in free-air geometry. [ABSTRACT FROM AUTHOR]

We present a case where alopecia occurred with severe seborrhoeic dermatitis associated with the commencement of combination antiretroviral therapy for acute retroviral syndrome. We postulate that the eruption could represent a novel manifestation in association with immunological response to antiretroviral therapy. [ABSTRACT FROM AUTHOR]

Although there are many published quality indicators (QIs) to assess the management of lung cancer, there is a paucity of relevant QIs specific to measuring the quality of radiotherapy (RT). We used the commonly accepted modified Delphi technique for structured consensus to develop a set of QIs and benchmarks designed to evaluate the RT process for lung cancer. This study used a modified Delphi technique composed of an international expert panel of radiation oncologists treating lung cancer, with a target of 40 participants, and intervening multidisciplinary steering committee review, with a minimum of nine stakeholders, that also included radiation therapists and medical physicists. The steering committee evaluated candidate QIs and benchmarks for inclusion in the first round from an initial systematic review with inclusion criteria of; QIs or guidelines with a potential to be developed into a QI and that were related to pre-treatment assessment, planning or delivery of radiotherapy. The expert panel ranked these in two rounds of electronic surveys for inclusion in the final set of QIs if a pre-defined consensus definition for importance was met by at least 70% of responses with a score of seven or more on a 9-point Likert scale. Feasibility and benchmarks met consensus criteria if at least 70% of responses are reported as three on a 3-point Likert scale. Systematic review resulted in 64 candidate QIs that were assessed by the steering committee, and it was concluded that 47 QIs and proposed benchmarks were needed for the initial survey round. There were 70 expert respondents over two surveys; 21.4% (n = 15), 30% (n = 21), and 48.6% (n = 34) were from Europe, the Americas, and Australasia, respectively. After the first survey round, 30 of 47 QIs met the criteria for inclusion in a second survey round. Consensus criteria and respondent comments were considered for QI inclusion and benchmarks, resulting in additional wording and benchmark amendments for the subsequent round. The final round survey resulted in 29 of 30 QIs reaching consensus (range 71-97%) for importance, with 12 of these QIs reaching a consensus of ≥90%. A QI for patients who underwent stereotactic ablative RT for non-small cell lung cancer having had a biopsy proven malignancy failed to reach consensus. Respondents assessed all 30 QIs as feasible and 27 suggested benchmarks met pre-defined inclusion criteria. The final set of QIs included descriptors for pre-treatment risk assessment, timing, treatment indications, treatment dose and fractionation, planning, treatment volumes, treatment delivery, and organization factors. Our developed RT-specific QIs offer a robust framework for evaluating and enhancing radiotherapy in lung cancer care. This initiative lays the groundwork for standardized quality assessments and improvements, aiming to elevate treatment outcomes across the board. [ABSTRACT FROM AUTHOR]

Stereotactic Ablative Body Radiotherapy (SABR) is an effective option in treating primary and metastatic liver cancers. Motion management and image guidance address liver deformation and target motion related to respiration and gastrointestinal motion. The primary aim of this study was to assess the dosimetric influence of using KIM, a real-time image guidance technology, over Cone Beam Cone Beam Tomography (CBCT). In this multi-institutional prospective trial, 32 patients with either hepatocellular carcinoma or oligometastatic liver disease suitable for SBRT using KIM guidance were enrolled, with each institution credentialled and treatment plans reviewed. Target motions were corrected during each fraction using KIM + external surrogate (a precision radiation medicine company or a technology company) gating, implanted fiducials serving as surrogates. A 3 – 5 mm gating threshold over 5 seconds was applied for beam-off and couch shifts, except in two cases where Breath-hold (BH) were inconsistent (15mm). Using a dose reconstruction method, the accuracy of KIM guided treatment was evaluated against standard of care relying on external surrogate. From January 2020 to November 2023, thirty-two patients were treated across six institutions in Australia, receiving 122 treatment fractions, with a median age of 66.5 years. The cases included 21 liver metastases and 11 hepatocellular carcinomas. Th majority of patients (25/32) had a single lesion and primarily treated in breath-hold (25/32) and free-breathing (5/32) technique, with a median dose of 50 Gy over 5 fractions (range = 27.5 – 51 Gy in 3 – 5 fractions) using a 2 arc VMAT technique. The mean lesion diameter was 41.1mm (range = 17 – 103mm). Two patients were treated using standard treatment using CBCT without KIM guidance. The median PTV margin used was 5mm. During 122 fractions, 107 motion correction events occurred in 25 of 32 patients (87%), with single events in 24 fractions and multiple events (up to four or more) in 30 fractions. To date, the evaluation of the first 20 patients demonstrated that all patients treated with KIM received doses within 5% of the planned dosimetry. Without KIM, two patients would have had > 5% dose errors to GTVD100 and one patient would have exceeded the stomach dose constraint. For two of 24 BH patients, KIM detected irregular motion, requiring PTV margin increases to 15 mm, motion undetectable with external surrogates alone. There was no > grade 2 toxicity related to radiation treatment observed in the patient cohort. This study demonstrates that integrating continuous KIM guidance enhances precision and confidence of liver SBRT delivery. Without continuous intrafraction image guidance, at least a 5mm PTV expansion would be advised to counter intrafraction motion. Future applications may include safe reduction of PTV margins and customization for individual patients. [ABSTRACT FROM AUTHOR]

Biology-guided radiotherapy (BgRT) is a new technology that delivers radiation based on positron emission tomography (PET) signal. Lutetium-177 (177Lu) prostate-specific membrane antigen (PSMA) is a novel theranostic treatment that demonstrated high response and low toxicities in patients with metastatic castrate-resistant prostate cancer. However, patients may be excluded from this theranostic treatment due to discordance between Gallium-68 (68Ga)-PSMA-11 and 18F-fluorodeoxyglucose (FDG) PET uptake at screening. Using the theranostic treatment alone on these excluded patients would result in untreated FDG-only avid tumor deposits. However, FDG-only avid tumor deposits may be treated with BgRT. This study investigates the feasibility of a combined theranostic/BgRT treatment to excluded patients with discordant uptake. Patients excluded from the LuPSMA clinical trial (ID ANZCTR12615000912583) were retrospectively reviewed. A hypothetical hybrid treatment was considered in which BgRT would supplement 177Lu-PSMA treatment in discordant FDG-avid tumors. In this treatment, FDG-only avid tumors would be treated with BgRT whereas PSMA-avid tumors would be treated with LuPSMA treatment (100% efficacy was assumed). PSMA PET uptake was mapped to the FDG PET frame of reference using deformable registration between the CT-component of the two PET scans. Gross tumor volume (GTV) of FDG-only avid tumors were contoured on the CT-component of the FDG PET/CT scan by a radiation oncologist. Biological tracking zones (BTZ) for BgRT dose delivery were generated from GTV outer margin expansion of 5 mm / 10 mm / 20 mm. Normalized SUV (nSUV) was calculated as the ratio of the maximum SUV inside the GTV to the mean of SUV inside the outer margin expansions. Tumors were considered suitable to BgRT if nSUV was larger than 3 and if the normal tissue surrounding the tumor was free of any PET signal inside the BTZ. Of 75 patients screened for LuPSMA treatment, 7 patients had discordant PSMA and FDG uptake, 6 of which had FDG-only avid tumors and were included in this study. In these 6 patients, 89 potential BgRT targets were identified. GTV volumes ranged from 0.3 cm3 to 186 cm3 (median GTV volume = 4.3 cm3, IQR = 2.2 cm3 – 7.4 cm3). SUVmax inside GTVs was between 3 and 12 (median SUVmax = 4.8, IQR = 3.9 – 6.2). With nSUV ≥ 3, 67% / 48% / 28% of all GTVs were free of FDG uptake within 5 mm / 10 mm / 20 mm from the tumor and therefore suitable to BgRT. Bone and lung sites were the best candidates for BgRT (27% / 18% of all tumors were bone / lung GTVs with nSUV ≥ 3 and were isolated from PET uptake within 5 mm). 67% of FDG-only avid tumors were suitable to BgRT treatment inside a BTZ generated from a margin expansion of 5 mm. BgRT treatment to FDG-only avid tumor in combination with Lutetium PSMA theranostic treatment is therefore feasible. [ABSTRACT FROM AUTHOR]

Purpose/objective(s): Biology-guided radiation therapy (BgRT) is a new technology that aims to deliver radiation based on detecting positron emissions in real time. BgRT combined with prostate specific membrane antigen (PSMA) PET/CT imaging may be an attractive option for prostate cancer patients with low-volume pelvic nodes and distant metastases since all lesions may be treated during the same session. This study investigates the feasibility of BgRT sequential boost to the PSMA-avid subvolume (PAS) in the prostate region. The ratio of standard uptake value (SUV) to background SUV is quantified, with specific focus on adjacent bladder uptake.Materials/methods: Patients enrolled in the ProPSMA prospective single-institution clinical trial underwent Ga-68-PSMA-11 PET scan at the time of prostate cancer diagnosis. Those with pelvic node or distant metastases were selected for analysis. PAS gross target volume (GTV) was delineated on the PET component of a PET/CT acquisition by using a PET edge tool in commercially available software. Three dimensional shells of thickness 5 mm, 10 mm and 20 mm were created by expanding the GTV to characterize the uptake background and to determine suitability of BgRT based on these tracking zones. Normalized SUV (nSUV) was calculated as the ratio of SUVmax in the GTV to SUVmean of the adjacent shell. Lesions with nSUV larger than 3 were defined to be suitable for BgRT. An increase in nSUV with increasing shell thickness indicates absence of uptake surrounding the GTV.Results: From the ProPSMA patient cohort of 89 patients, 24 patients had at least one pelvic nodal or distant metastases. PAS GTV volume ranged from 1 cc to 147 cc (median = 25 cc, IQR = 12 cc - 62 cc). GTV SUVmax varied from 6.4 to 80 (median = 21.5; IQR = 14 - 33). nSUV ranged from 3.4 to 21.2 (median = 6.4; IQR = 4.9 - 8.5), from 4.1 to 20.9 (median = 8.6; IQR = 6 - 10.5), and from 2.8 to 31.4 (median = 8.2; IQR = 5.4 - 13.8) in 5 mm, 10 mm, and 20 mm shell, respectively. Moreover, 100%, 100%, and 96% of lesions had nSUV greater than 3 in a shell thickness of 5 mm, 10 mm, and 20 mm, respectively. nSUV increased from the 5 mm shell to the 10 mm shell in 75% of patients and from the 10 mm shell to the 20 mm in 46% patients, indicating the absence of bladder uptake.Conclusion: An nSUV greater than 3 was achieved in more than 95% of all GTVs for all shell thicknesses investigated in this study, which suggests that PSMA-guided BgRT is a feasible modality for sequential boost directed at the dPSMA-avid subvolume in the prostate region. If bladder proximity impacts geometric specificity of BgRT delivery or if greater tumor-to-background contrast is desired, additional refinements may be required. These may include modifications to the BgRT algorithm that enable masking of the bladder. Clinical trial number ACTRN12617000005358. [ABSTRACT FROM AUTHOR]

Poster Highlights: Poster highlights 15: Particles and microbeams OC-0474: Feasibility of prostate SBRT with DIL boost in various platforms: A Crowd Knowledge based study A. Savini, E. Villaggi, O. Blanck, C. Moustakis, V. Hernandez, S. Russo, M. Esposito, R. De Blas Piñol, N. Hardcastle, J. Saez, R. Doro, M.D. Falco, V. Silvestri, B. Nardiello, S. Broggi, L. Strigari, S. Cilla, S. Strolin, M. Stasi, P. Mancosu. [Extracted from the article]