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Purpose To evaluate the electromagnetic (EM) tracking of endoscopes and applicators as a method of positioning a high dose rate (HDR) luminal applicator. Method An anatomical phantom consisting of a rigid trachea and flexible esophagus was used to compare applicator placement measurements using EM tracking vs the traditional method using two-dimensional (2D) fluoroscopy and surface skin markers. The phantom included a tumor in the esophagus and several pairs of optically visible points inside the lumen that were used to simulate proximal and distal ends of tumors of varying lengths. The esophagus tumor and lung points were visible on a computed tomography (CT) image of the phantom, which was used as ground truth for the measurements. The EM tracking system was registered to the CT image using fiducial markers. A flexible endoscope was tracked using the EM system and the locations of the proximal and distal ends of the tumor identified and this position recorded. An EM-tracked applicator was then inserted and positioned relative to the tumor markings. The applicator path was mapped using the EM tracking. The gross tumor length (GTL) and the distance between the first dwell position and distal edge of tumor (offset) were measured using the EM tracking and 2D fluoroscopy methods and compared to the same measurements on the CT image. Results The errors in GTL using EM tracking were on average -0.5 ± 1.7 mm and 0.7 ± 3.6 mm for esophagus and lung measurements, similar to errors measured using the 2D fluoroscopy method of -0.9 ± 1.2 mm and 3.4 ± 4.4 mm. Offset measurements were slightly larger while using EM tracking relative to the fluoroscopy method but these were not statistically significant. Conclusions Electromagnetic tracking for placement of lumen applicators is feasible and accurate. Tracking of the endoscope that is used to identify the proximal and distal ends of the tumor and of the applicator during insertion generates accurate three-dimensional measurements of the applicator path, GTL and offset. Guiding the placement of intraluminal applicators using EM navigation is potentially attractive for cases with complex insertions, such as those with nonlinear paths or multiple applicator insertions.

Purpose To develop a treatment planning platform for episcleral Collaborative Ocular Melanoma Study plaque therapy in an established treatment planning software and to improve an existing quality assurance (QA) process for nonuniformly loaded plaques that measures air kerma strengths (AKSs) and loading profile. Materials and Methods Treatment planning is performed in Pinnacle using scripts that let the planner choose plaque size and notching. Scripts load seed positions for each plaque and five source groups corresponding to available stock seeds that can be placed into each seed position. Contours are loaded that display the model eye and the plaque itself. Plaque QA is performed using a modification of our previous pinhole apparatus by replacing x-ray film exposure with an optical camera and scintillating film system. The captured image is processed to remove background and to correct the intensity of seeds on the plaque periphery. Measured total optical counts provide an estimate of total plaque AKS. Results Treatment planning of eye plaques using Pinnacle, in conjunction with our stock inventory of seeds, is established as standard practice at our center. Planned plaques can vary from uniformly loaded to asymmetrically loaded notched plaques. Using the optical camera system for assessment of the seed loadings has decreased QA time from 40 min/plaque to 10 min/plaque. Total AKS of each plaque can be measured using the optical camera with an accuracy of 10%. Conclusions Treatment planning is performed on a Health Canada–approved software that accommodates nonuniform plaque loading. Optical imaging of the plaque provides absolute total AKS and the relative seed arrangement in the plaque.

To report dosimetry, preliminary toxicity and health-related quality of life (HRQoL) outcomes of tumor-targeted dose-escalation delivered by integrated boost volumetric arc therapy (IB-VMAT) or MR-guided HDR brachytherapy (HDR) boost for prostate cancer.Patients diagnosed with localized prostate cancer, with at least 1 identifiable intraprostatic lesion on multiparametric MRI (mpMRI) were enrolled in a prospective non-randomized phase II study. All patients received VMAT to the prostate alone (76 Gy in 38 fractions) plus a GTV boost: IB-VMAT (95 Gy in 38 fractions) or MR-guided HDR (10 Gy single fraction). GTV was delineated on mpMRI and deformably registered to planning CT scans. Comparative dosimetry using EQD2 assuming α/β 3 Gy was performed. Toxicity and health-related quality of life data (HRQoL) data were collected using CTCAE v.4.0, International Prostate Symptom Score (IPSS) and the Expanded Prostate Index Composite (EPIC).Forty patients received IB-VMAT and 40 HDR boost. Organs at risk and target minimal doses were comparable between the two arms. HDR achieved higher mean and maximal tumor doses (p 0.05). Median follow-up was 31 months (range 25-48); Acute grade G2 genitourinary (GU) toxicity was 30% and 37.5% in IB-VMAT and HDR boost, while gastrointestinal (GI) toxicity was 7.5% and 10%, respectively. Three patients developed acute G3 events, two GU toxicity (one IB-VMAT and one HDR boost) and one GI (IB-VMAT). Late G2 GU toxicity was 25% and 17.5% in the IB-VMAT and HDR boost arm and G2 GI was 5% and 7.5%, respectively. Two patients, both on the IB-VMAT arm, developed late G3 toxicity: one GI and one GU. No statistically significant difference was found in HRQoL between radiotherapy techniques (p 0.2). Urinary and bowel HRQoL domains in both groups declined significantly by week 6 of treatment in both arms (p 0.05) and recovered baseline scores at 6 months.Intraprostatic tumor dose escalation using IB-VMAT or MR-guided HDR boost achieved comparable OAR dosimetry, toxicity and HRQOL outcomes, but higher mean and maximal tumor dose were achieved with the HDR technique. Further follow-up will determine long-term outcomes including disease control.

OBJECTIVE The objective of this study was to determine the outcomes of patients with unresectable endometrial cancer managed with definitive or neoadjuvant radiation (RT) and/or chemotherapy. MATERIALS AND METHODS Patients with unresectable stages II to IVA endometrial cancer who were treated with curative intent between January 2000 and March 2018 were identified. Overall survival (OS) and disease-free survival (DFS) were analyzed using the Kaplan-Meier method and compared using the log-rank test. Multivariate logistic regression analysis was performed to identify factors associated with receipt of surgery. Multivariate Cox regression analysis was performed to identify factors associated with OS and DFS. RESULTS Of the 59 patients identified, the median age was 63 years (range: 37 to 88 y) and histology was endometrioid in 59%. Median follow-up was 2.2 years (range: 0.3 to 9.8 y). Seventeen patients (29%) received neoadjuvant chemotherapy, 28 (47%) neoadjuvant radiation, and 14 (24%) definitive RT; 39 (66%) underwent surgery. Patients who received surgery had higher 3-year OS and DFS than those who did not (84% vs. 41%; P

Purpose To determine the dosimetric feasibility of dose-escalated MRI-guided high-dose-rate brachytherapy (HDR-BT) focal monotherapy for prostate cancer (PCa). Methods In all patients, GTV was defined with mpMRI, and deformably registered onto post-catheter insertion planning MRI. PTV included the GTV plus 9mm craniocaudal and 5mm in every other direction. In discovery-cohort, plans were obtained for each PTV independently aiming to deliver ⩾16.5Gy/fraction (two fraction schedule) while respecting predefined organs-at-risk (OAR) constraints or halted when achieved equivalent single-dose plan (24Gy). Dosimetric results of original and focal HDR-BT plans were evaluated to develop a planning protocol for the validation-cohort. Results In discovery-cohort (20-patients, 32-GTVs): PTV D95% ⩾16.5Gy could not be reached in a single plan (3%) and was accomplished (range 16.5–23.8Gy) in 15 GTVs (47%). Single-dose schedule was feasible in 16 (50%) plans. In the validation-cohort (10-patients, 10-GTVs, two separate implants each): plans met acceptable and ideal criteria in 100% and 43–100% respectively. Migration to single-dose treatment schedule was feasible in 7 implants (35%), without relaxing OAR's constraints or increasing the dose (D100% and D35%) to mpMRI-normal prostate ( p >0.05). Conclusion Focal ablative dose-escalated radiation is feasible with the proposed protocol. Prospective studies are warranted to determine the clinical outcomes.

Purpose The purpose of this study was to implement a machine learning model to predict skin dose from targeted intraoperative (TARGIT) treatment resulting in timely adoption of strategies to limit excessive skin dose. Methods A total of 283 patients affected by invasive breast carcinoma underwent TARGIT with a prescribed dose of 6 Gy at 1 cm, after lumpectomy. Radiochromic films were used to measure the dose to the skin for each patient. Univariate statistical analysis was performed to identify correlation of physical and patient variables with measured dose. After feature selection of predictors of in vivo skin dose, machine learning models stepwise linear regression (SLR), support vector regression (SVR), ensemble with bagging or boosting, and feed forward neural networks were trained on results of in vivo dosimetry to derive models to predict skin dose. Models were evaluated by tenfold cross validation and ranked according to root mean square error (RMSE) and adjusted correlation coefficient of true vs predicted values (adj-R2 ). Results The predictors correlated with in vivo dosimetry were the distance of skin from source, depth-dose in water at depth of the applicator in the breast, use of a replacement source, and irradiation time. The best performing model was SVR, which scored RMSE and adj-R2 , equal to 0.746 [95% confidence intervals (CI), 95% CI 0.737,0.756] and 0.481 (95% CI 0.468,0.494), respectively, on the tenfold cross validation. Conclusion The model trained on results of in vivo dosimetry can be used to predict skin dose during setup of patient for TARGIT and this allows for timely adoption of strategies to prevent of excessive skin dose.

Purpose To report on single-fraction stereotactic body radiotherapy (RT) (SBRT) with flattening filter (FF)–free (FFF) volumetric modulated arc therapy (VMAT) for lung cancer and to compare dosimetric results with VMAT with FF. Methods and materials Overall, 25 patients were treated with 6-MV FFF VMAT (Varian TrueBeam STx LINAC) to a prescribed dose of 24 Gy in a single fraction. Treatment plans were recreated using FF VMAT. Dose-volume indices, monitor units (MU), and treatment times were compared between FFF and FF VMAT techniques. Results Dose constraints to PTV, spinal cord, and lungs were reached in FFF and FF plans. In FFF plans, average conformity index was 1.13 (95% CI: 1.07 to1.38). Maximum doses to spinal cord, heart, esophagus, and trachea were 2.9 Gy (95% CI: 0.4 to 6.7 Gy), 0.8 Gy (95% CI: 0 to 3.6 Gy), 3.3 Gy (95% CI: 0.02 to 13.9 Gy), and 1.5 Gy (95% CI: 0 to 4.9 Gy), respectively. Average V7 Gy, V7.4 Gy, and mean dose to the healthy lung were 126.5 cc (95% CI: 41.3 to 248.9 cc), 107.3 cc (95% CI: 18.7 to 232.8 cc), and 1.1 Gy (95% CI: 0.3 to 2.2 Gy), respectively. No statistically significant differences were found in dosimetric results and MU between FF and FFF treatments. Treatment time was reduced by an average factor of 2.31 (95% CI: 2.15 to 2.43) from FF treatments to FFF, and the difference was statistically significant. Conclusions FFF VMAT for lung SBRT provides equivalent dosimetric results to the target and organs at risk as FF VMAT while significantly reducing treatment time.

For volumes up to 2 cm3 of the bladder and possibly up to 5 cm3 of the rectum, doses computed from the whole organ were good estimates of the doses in the wall in cervix brachytherapy, and there were no significant differences between patients treated with or without interstitial needles.

PURPOSE: MR-guided brachytherapy (MRgBT) with interstitial needles is associated with improved outcomes in cervical cancer patients. However, there are implementation barriers, including magnetic resonance (MR) access, practitioner familiarity/comfort, and efficiency. This study explores a graded MRgBT implementation strategy that included the adaptive use of needles, strategic use of MR imaging/planning, and team learning.METHODS AND MATERIALS: Twenty patients with cervical cancer were treated with high-dose-rate MRgBT (28 Gy in four fractions, two insertions, daily MR imaging/planning). A tandem/ring applicator alone was used for the first insertion in most patients. Needles were added for the second insertion based on evaluation of the initial dosimetry. An interdisciplinary expert team reviewed and discussed the MR images and treatment plans.RESULTS: Dosimetry-trigger technique adaptation with the addition of needles for the second insertion improved target coverage in all patients with suboptimal dosimetry initially without compromising organ-at-risk (OAR) sparing. Target and OAR planning objectives were achieved in most patients. There were small or no systematic differences in tumor or OAR dosimetry between imaging/planning once per insertion vs. daily and only small random variations. Peer review and discussion of images, contours, and plans promoted learning and process development.CONCLUSIONS: Technique adaptation based on the initial dosimetry is an efficient approach to implementing MRgBT while gaining comfort with the use of needles. MR imaging and planning once per insertion is safe in most patients as long as applicator shifts, and large anatomical changes are excluded. Team learning is essential to building individual and programmatic competencies.

Purpose To assess changes in implant and treatment volumes through the course of a prostate high-dose-rate brachytherapy procedure and their impact on plan quality metrics. Methods and Materials Sixteen MRI-guided high-dose-rate procedures included a post-treatment MR (ptMR) immediately after treatment delivery (135 min between MR scans). Target and organs at risk (OARs) were contoured, and catheters were reconstructed. The delivered treatment plan was applied to the ptMR image set. Volumes and dosimetric parameters in the ptMR were evaluated and compared with the delivered plan using a paired two-tailed t-test with p Results An average increase of 8.9% in prostate volume was observed for whole-gland treatments, resulting in reduction in coverage for both prostate and planning target volume, reflected in decreased V100 (mean 3.3% and 4.6%, respectively, p Conclusions Volumetric changes were observed during the time between planning MR and ptMR. Nonetheless, treatment plans for both whole- and partial-gland therapies remained clinically acceptable. These results apply to clinical settings in which patients remain in the same position and under anesthesia during the entire treatment process.

Purpose To describe the incidence and type of brachytherapy patient safety events over 10 years in an academic brachytherapy program. Methods and Materials Brachytherapy patient safety events reported between January 2007 and August 2016 were retrieved from the incident reporting system and reclassified using the recently developed National System for Incident Reporting in Radiation Treatment taxonomy. A multi-incident analysis was conducted to identify common themes and key learning points. Results During the study period, 3095 patients received 4967 brachytherapy fractions. An additional 179 patients had MR-guided prostate biopsies without treatment as part of an interventional research program. A total of 94 brachytherapy- or biopsy-related safety events (incidents, near misses, or programmatic hazards) were identified, corresponding to a rate of 2.8% of brachytherapy patients, 1.7% of brachytherapy fractions, and 3.4% of patients undergoing MR-guided prostate biopsy. Fifty-one (54%) events were classified as actual incidents, 29 (31%) as near misses, and 14 (15%) as programmatic hazards. Two events were associated with moderate acute medical harm or dosimetric severity, and two were associated with high dosimetric severity. Multi-incident analysis identified five high-risk activities or clinical scenarios as follows: (1) uncommon, low-volume or newly implemented brachytherapy procedures, (2) real-time MR-guided brachytherapy or biopsy procedures, (3) use of in-house devices or software, (4) manual data entry, and (5) patient scheduling and handoffs. Conclusions Brachytherapy is a safe treatment and associated with a low rate of patient safety events. Effective incident management is a key element of continuous quality improvement and patient safety in brachytherapy.

Purpose. To report our experience with high dose rate endobronchial brachytherapy (HDR-EBBT) and to assess its efficacy and tolerability with possibility of its use in selected cases with curative intent.Method. Retrospective review of patients with endobronchial tumors treated at our institution in 2007–2013 with HDR-EBBT. Subjective response and treatment related toxicity were extracted from patients’ records. Clinical response was evaluated by chest CT +/− bronchoscopy 2-3 months after treatment. Local control (LC) and overall survival (OS) were analyzed.Results. Overall 23 patients were identified. Ten patients were treated with curative intent, in 8 of them HDR-EBBT was combined with external beam radiotherapy. Short term palliation was as follows: dyspnea (13/15), cough (12/14), and hemoptysis (3/3). Seventeen patients were evaluated, of whom 9 (53%) showed complete response. Four patients developed local failure (only 1 of them treated with curative intent) and were salvaged with HDR-EBBT (n=1), chemotherapy (n=2), and laser (n=1). Among patients treated with curative intent, the 2-year LC and OS were 89% and 67%, respectively, and 2 out of 4 deaths were cancer-related. Late toxicity included bronchial stenosis (n=1). Only 1 patient had fatal hemoptysis and postmortem examination indicated local recurrence.Conclusion. HDR-EBBT is promising treatment with tolerable complication if used in properly selected patients.

Purpose: EBT2 radiochromic films were studied and used for in vivo dosimetry in targeted intraoperative radiotherapy (TARGIT), a technique in which the Intrabeam system (Carl Zeiss, Oberkochen, Germany) is used to perform intraoperative partial breast irradiation with x-rays of 50 kV{sub p}. Methods: The energy of the radiation emitted by the Intrabeam with the different spherical applicators, under 1 and 2 cm of solid water, and under the tungsten impregnated rubber used for shielding of the heart in TARGIT of the breast, was characterized with measurements of half-value layer (HVL). The stability of response of EBT2 was verified inside this range of energies. EBT2 films were calibrated using the red and green channels of the absorption spectrum in the 0-20 Gy dose range delivered by the Intrabeam x-rays. The dependence of film response on temperature during irradiation was measured. For in vivo dosimetry, pieces of radiochromic films wrapped in sterile envelopes were inserted after breast conserving surgery and before TARGIT into the excision cavity, on the skin and on the shielded pectoralis fascia for treatments of the left breast. Results: HVLs of the Intrabeam in TARGIT of the breast correspond to effective energies of 20.7-36.3 keV. The response of EBT2more » was constant inside this range of energies. We measured the dose to the target tissue and to organs at risk in 23 patients and obtained an average dose of 13.52 {+-} 1.21 Gy to the target tissue. Dose to the skin in close proximity to the applicator was 2.22 {+-} 0.97 Gy, 0.29 {+-} 0.17 Gy at 5-10 cm from the applicator, and 0.08 {+-} 0.07 Gy at more than 10 cm from the applicator. Dose to the pectoral muscle for left breast treatment was 0.57 {+-} 0.23 Gy. Conclusions: Our results show that EBT2 films are accurate at the beam energies, dose range, and irradiation temperature found in TARGIT and that in vivo dosimetry in TARGIT with EBT2 films wrapped in sterile envelopes is a feasible procedure. Measured dose to the organs at risk indicates that the technique is safe from side effects to the skin and the heart.« less

Magnetic resonance (MR) imaging is routinely employed in the design of radiotherapy (RT) treatment plans for many disease sites. It is evident that tighter integration of MR imaging into the RT process would increase confidence in dose placement and facilitate the integration of new MR imaging information (including anatomical and functional imaging) into the therapy process. To this end, a dedicated MR-guided RT (MRgRT) facility has been created that integrates a state-of-the-art linear accelerator delivery system, high-dose rate brachytherapy afterloader, and superconducting MR scanner to allow MR-based online treatment guidance, adaptive replanning, and response monitoring while maintaining the clinical functionality of the existing delivery systems. This system is housed within a dedicated MRgRT suite and operates in a coordinated fashion to assure safe and efficient MRgRT treatments.

We report clinical observations of a technique using an MRI-only workflow for catheter insertion and treatment planning in patients receiving standard-care high-dose-rate brachytherapy before external beam radiotherapy for prostate cancer.Forty patients with intermediate or high-risk prostate cancer were enrolled on a prospective clinical trial approved by our institution's research ethics board. Multiparametric MRI with stereotactic navigation was used to guide insertion of brachytherapy catheters, followed by MRI-based treatment planning.Sixty-two implants were performed. Median catheter insertion + imaging time was 100 minutes, and overall anesthesia time was 4.0 hours (range, 2.1-6.9 hours). MRI at the time of brachytherapy restaged 14 patients (35%) who were found to have a higher stage of disease. In 6 patients, this translated in directed insertion of brachytherapy catheters outside the prostate boundary (extracapsular disease [n = 2] or seminal vesicle invasion [n = 4]). Most patients (80%) had gross tumor visible on MRI, which influenced catheter insertion and treatment planning. MRI depicted postimplant anatomic boundaries clearly, with the exception of the apical prostate which was blurred by trauma after catheter insertion. Conventional dose-planning objectives for the rectum (V751.0 cc) were difficult to achieve, but toxicities were low (acute grade ≥ 2 genitourinary = 20%, late grade ≥ 2 genitourinary = 15%, and late grade ≥ 2 gastrointestinal = 7%). Urethral trauma visualized on MRI led to two transient Grade 3 events.Despite a standard-care approach, MRI acquired throughout the procedure altered catheter insertion and dose-planning strategies. An MRI-only workflow is feasible but must be streamlined for broader acceptance.

leads to more conservative treatments. For pelvic tumors, measurement of the rectal wall dose will facilitate optimal treatment delivery. We report on the clinical performance of a fibre optic dosimetry (FOD ) system customized to measure the dose in real time in an array configuration. This system enables definitive assessment of the dose delivered, with the potential for intervention if required. Materials and Methods: An array of FODs in an insertable applicator has been designed and built. The clinician can select to position all the dosimeters along the anterior wall of the rectum or in any other arrangement. Dosimeters were optically interfaced to a light detection system, located outside the treatment bunker. Customized software recorded the dose from each dosimeter as the real time dose rate and as the accumulated dose at that point. Prior to use the dosimeters were simultaneously calibrated in a purpose built jig. Results: The performance of the array was demonstrated first by simulating brachytherapy treatments in a water phantom. Preliminary clinical trial with gynecological patients established that rectal wall dose mapping was convenient and accurate. In Figure 1 the radioopaque markers on the end of the rectal applicator are visible.

Purpose: An MRI on rails is being installed at our institution to provide MR‐guided brachytherapy and teletherapy (MRgRT). The facility is comprised of collinear brachytherapy, MR‐Sim, and linac suites. The MR‐on‐rails translates into the adjacent suites for imaging. An existing bunker and adjacent space were renovated to permit the MR to be moved away from the linac during irradiation. This work describes the design and radiation shielding characteristics of the linac suite within the MRgRT facility. Methods: The original linac vault was designed with a two‐corner maze design to operate at 18 MV. The maze was removed and replaced with three direct‐shielded doors: a sliding console door allow for personnel and gurney access to the bunker; and two double sliding doors through which the MRI translates. The double doors employ an S‐shaped coupling surface to minimize radiation leakage when they are closed. These doors are also RF‐shielded as part of the MR RF cage. The shielding was designed for a workload of 5 × 106 cGy per year; 6 MV beam; maximum dose rate: 1400 MU/min; shielding level 0.05 mSv/year for members of the public and 1 mSv/year for nuclear energy workers. Results: The total thickness of the linac‐MRI sliding doors was 7 inches of lead and 2 inches of stainless steel, producing an equivalent thickness of 8 inches (20.3 cm) of lead. The dose rate at the distal surface of the linac‐MR door is 0.08 mSv/year or 10.9 μSv/hr. The final design includes a copper RF shield and bladder to provide RF shielding. Conclusion: A facility comprising three collinear brachytherapy, MR‐Sim, and linac facility has been designed to meet radiation and radiofrequency shielding limits.

Purpose: Enhanced radiation and light field quality assurance (QA) procedures have been developed and implemented utilizing amorphous siliconelectronic portal imaging devices(EPID). This effort was motivated by the fact that film exposure coupled with hand measurements are extremely time consuming and prone to many sources of error. Method and Materials: The EPID based QA procedure uses specially designed acrylic test templates, containing radio‐opaque led bars to register the position of the optical field. Images of these templates were acquired with the EPID on both Varian and Elekta linear accelerators. A MATLab based computer application was used to automatically assess light/radiation field congruence, radiationfield sizes and optical field size and positioning. A three‐month pilot study using two Varian accelerators to assess both 6 MV and 18 MV photon energies was performed to validate the EPID QA procedure's efficacy and quantify its efficiency relative to film QA procedures. Results: The pilot study verified that the EPID QA system results are congruent with the hand measurements obtained from a detailed analysis of film QA measurements. Light/radiation congruence measurement performed using an EPID exhibited an absolute mean deviation of 0.37 ± 0.37 mm (1σ), relative to the film measurements.EPID based radiationfield size assessments produced an absolute discrepancy of 0.57 ± 0.44mm (1σ), while film measurements yielded an absolute discrepancy of 0.61 ± 0.55mm (1σ), relative to measurements acquired using RIT software.EPID based measurements were found to be more efficiently performed, reducing the set‐up and analysis time by 55% compared to film. Conclusions: The enhanced EPID QA system can effectively replace film in routine quality assurance tasks for radiation and optical fields. This procedure saves Princess Margaret Hospital 4 man‐hours per week, and provides a user‐independent analysis procedure for objectively assessing routine QA results.