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To report on brachytherapy (BT) workflows for image-based treatments of locally advanced cervical cancer (CC) in Canada.Medical Physicists in every Canadian cancer center were contacted and those with a CC-BT program were emailed a 44-item electronic questionnaire surveying workflow patterns including: fractionation schedules, prescription, equipment, imaging, and treatment delivery.Of 47 centers contacted, all 34 who performed CC-BT participated in the survey. Brachytherapy boost, following external beam treatments, was delivered using high-dose-rate (HDR); one center also used pulsed-dose-rate. Intracavitary and/or interstitial treatments were done in 47% centers for 25-80% of their patients. All centers used image-based planning: CT (32%), CT planned with MRI for contouring (47%), MRI (18%), or cone beam CT (3%). For those performing volume-based planning (74%), the contours commonly included Clinical Target Volume (CTV)-High Risk (HR), CTV-Intermediate Risk, rectum, sigmoid, and bladder. The most common HDR dose-fractionation schedule was 7 [4.6 - 10] Gy in 4 [3 - 6] fractions with radiobiological dose prescriptions performed in 62% centers. Medical physics contribution was significant during most activities along the BT treatment pathway in all centers, especially in planning (88%), second checks (68%), and during treatment delivery (88%).Compared to previous surveys, there is an increasing trend in the use of image-based volumetric planning, interstitial procedures, and radiobiological dose prescription. Cervical cancer brachytherapy in Canada is becoming more streamlined with the use of international practice guidelines. Involvement of medical physicists is vital to all stages of CC-BT, including program implementation, routine quality control, dosimetry, and treatment delivery.

Purpose The aim of this study was to develop an automated dose optimization algorithm, powered by simulated annealing, for inverse planning of ocular plaque brachytherapy treatments, to improve tumor coverage and critical structure sparing for reduced treatment-related morbidity. Methods and Materials A simulated annealing based algorithm was built and evaluated by finding variable seed strengths that maximized dose uniformity across tumor base for model cases of various tumor heights and plaque sizes. This problem assessed its potential to find the minima in the energy function using differential loading. The algorithm was further developed to decrease doses to critical structures while maintaining desired tumor coverage. Doses to the optic disc and fovea were compared to those using uniform seed strengths for various model cases. Finally, 10 retrospective patient cases treated with uniform seed strengths were replanned with the developed algorithm to evaluate effectiveness for clinical application. Results The developed algorithm achieved dose reductions of up to 37.3% and 39.6% to the optic disc and fovea, respectively, compared to those using uniform seed strengths, depending on the tumor and plaque size used for the model cases. Applying the algorithm to 10 clinical scenarios resulted in dose reductions of 14% to the optic disc and fovea relative to clinical treatments performed with uniform seed strengths. Conclusions The developed automatic dose optimization routine was able to achieve significant dose reductions to the critical structures relative to using uniformly loaded plaques both in the model and in the clinical cases.

Purpose The purpose of the study was to determine dosimetric effects of performing concurrent I-125 Collaborative Ocular Melanoma Study plaque brachytherapy and vitrectomy with replacement using silicone oil, previously shown to be a means of shielding uninvolved parts of the eye. Methods and Materials Monte Carlo simulations using MCNP6 were performed to compare the dosimetry with all eye materials assigned as water, and for the vitreous (excluding the tumor), composed of polydimethylsiloxane oil for three generic, one large tumor, and two patient geometry scenarios. Dose was scored at the tumor apex, along the sclera, and within a 3D grid encompassing the eye. The assessed patient cases included vitrectomies to treat intraocular pathologies; not to enhance attenuation/shielding. Results The doses along the sclera and for the entire eye were decreased when the silicone oil replaced the vitreal fluid, with a maximum decrease at the opposite sclera of 63%. Yet, absolute changes in dose to critical structures were often small and likely not clinically significant. The dose at the tumor apex was decreased by 3.1–9.4%. Dose was also decreased at the edges of the tumor because of decreased backscatter at the tumor-oil interface. Conclusions Concurrent silicone vitrectomy was found to reduce total radiation dose to the eye. Based on current radiation retinopathy predictive models, the evaluation of the absolute doses revealed only a subset of patients in which a clinically significant difference in outcomes is expected. Furthermore, the presence of the silicone oil decreased dose to the tumor edges, indicating that the tumor could be underdosed if the oil is unaccounted for.

The GEC-ESTRO recommendation in cervical cancer treatment planning, including external beam radiotherapy and brachytherapy boosts, is to use radiobiological dose calculations. Such calculations utilize the linear-quadratic model to estimate the effect of multiple cellular response factors and dose delivery parameters. The radiobiological parameters utilized in these calculations are literature values estimated based on clinical and experimental results. However, the impact of the uncertainties associated with these parameters is often not fully appreciated. This review includes a summary of the radiobiological dose calculation (for both high-dose-rate and pulsed-dose-rate brachytherapy boost treatments) for cervical cancer and a compilation of the reported values of the associated parameters. As discrepancies exist between conventionally recommended and published values, equivalencies between current brachytherapy boosts may be imprecise and could create underappreciated uncertainties in the radiobiological dose calculations. This review highlights these uncertainties by calculating the radiobiological dose delivered by the brachytherapy boost when assuming different radiobiological parameter values (within the range reported by previous research). Furthermore, conventional treatment planning does not consider the effects of proliferation of the tumor over the treatment time, which can significantly decrease its radiobiological dose and can introduce an additional variance of over 7 Gy10. Further investigation of uncertainties in parameter values and modifications of current dose models could improve the accuracy of radiobiological dose calculation.

Purpose To report on the importance of cancer location from diagnostic prostate biopsies in predicting biochemical relapse for patients treated with 125 I seed implant brachytherapy as monotherapy for favorable risk disease; specifically, to assess the clinical significance of potentially underdosing the base region of the prostate gland. Methods and Materials Of 1145 consecutive patients, 846 had pretreatment biopsies allowing for sextant analysis and consequent evaluation of biochemical failure tendencies. Biochemical failure was defined as a posttreatment rise in the nadir prostate-specific antigen (PSA) by at least 2 ng/mL. Patient and tumor characteristics, dosimetry, the use of hormone therapy, source strength, and postimplant PSA kinetics were analyzed between sextant subgroups. Results Sixty-two patients (7.3%) with sextant pathology had biochemical failure. There was no significant difference between the failure locations. There were 528 patients (62.4%) with some element of base involvement (BI), and 318 patients (37.6%) with no evidence of BI. Of the 62 patients with biochemical failure, 42 (67.7%) showed BI on biopsy and 20 (32.3%) had no BI. The 10-year relapse-free survival rate is 88.2% (95% confidence interval: 84.3%, 92.2%) and 92.0% (95% confidence interval: 88.4%, 95.8%) for the BI and no BI groups, respectively ( p = 0.17). The mean D90 delivered to the base, midgland, and apex was 140.8 (±21.8) Gy, 170.8 (±22.5) Gy, and 177.9 (±29.5) Gy, respectively, for all patients. Conclusions There are no significantly worse outcomes for patients treated with an 125 I seed implant for favorable risk prostate cancer with some element of BI, despite lower doses of radiation delivered to the base region.

Purpose To experimentally assess the performance of the Advanced Collapsed-cone Engine (ACE) for 192Ir high-dose-rate brachytherapy treatment planning of nonmelanoma skin cancers of the scalp. Methods and Materials A layered slab phantom was designed to model the head (skin, skull, and brain) and surface treatment mold using tissue equivalent materials. Six variations of the phantom were created by varying skin thickness, skull thickness, and size of air gap between the mold and skin. Treatment planning was initially performed using the Task Group 43 (TG-43) formalism with CT images of each phantom variation. Doses were recalculated using standard and high accuracy modes of ACE. The plans were delivered to Gafchromic EBT3 film placed between different layers of the phantom. Results Doses calculated by TG-43 and ACE and those measured by film agreed with each other at most locations within the phantoms. For a given phantom variation, average TG-43– and ACE-calculated doses were similar, with a maximum difference of (3 ± 12)% (k = 2). Compared to the film measurements, TG-43 and ACE overestimated the film-measured dose by (13 ± 12)% (k = 2) for one phantom variation below the skull layer. Conclusions TG-43– and ACE-calculated and film-measured doses were found to agree above the skull layer of the phantom, which is where the tumor would be located in a clinical case. ACE appears to underestimate the attenuation through bone relative to that measured by film; however, the dose to bone is below tolerance levels for this treatment.

Purpose To explore maximum high-risk clinical target volume (HR-CTV) doses that can be practically achieved when organs at risk (OARs; bladder, rectum, and sigmoid) doses are allowed to equal current recommended thresholds in MRI-based intracavitary brachytherapy (BT) planning for cervical cancer. Methods and Materials Planning MRI sets were retrieved for 21 patients who received pulsed-dose-rate BT boost. Plans were generated using manual optimization (MO) by adjusting dwell positions and times to obtain the prescribed HR-CTV isodose that includes 90% of target ( D 90 ) coverage of 35 Gy while limiting OAR doses to below recommended tolerances (prescribed dose target [TGT] plans). Additional planning was performed with automatic volume optimization (VO) to evaluate target coverage relative to the MO plans. The MO and VO approaches were then applied with the objective of obtaining the highest possible HR-CTV coverage when OAR doses were allowed to equal threshold tolerance values (maximized [MAX] plans). A two-tailed paired t test was performed to determine the statistical significance of the results; significance level set at p Results MO and VO planning techniques could conform HR-CTV D 90 to the prescribed dose quite similarly for TGT plans. Using the MAX approach, the HR-CTV D 90 could be increased by 30% and 37% for MO and VO, respectively, without exceeding OAR thresholds. Sigmoid and often rectum were the dose-limiting structures during MAX planning. Conclusions Simple differences in the approach to volumetric MRI-based cervix BT treatment planning can impact HR-CTV D 90 . Consequently, dose escalation for MRI-guided cervix BT appears feasible in this manner should clinical circumstances warrant.