Current and Emerging Radiotherapy Options for Uveal Melanoma.

What treatment options are there for patients having uveal melanoma? A randomized, prospective, multi-institutional clinical trial (COMS) showed no difference in survival between brachytherapy and enucleation for medium-sized lesions. With the obvious benefit of retaining the eye, brachytherapy has flourished and many different approaches have been developed such as low-dose-rate sources using alternate low-energy photon-emitting radionuclides, different plaque designs and seed-loading techniques, high-dose-rate brachytherapy sources and applicators, and low- and high-dose-rate beta-emitting sources and applicators. There also have been developments of other radiation modalities like external-beam radiotherapy using linear accelerators with high-energy photons, particle accelerators for protons, and gamma stereotactic radiosurgery. This article examines the dosimetric properties, targeting capabilities, and outcomes of these approaches. The several modalities examined herein have differing attributes and it may be that no single approach would be considered optimal for all patients and all lesion characteristics.

Generation and comparison of 3D dosimetric reference datasets for COMS eye plaque brachytherapy using model-based dose calculations.

PURPOSE: A joint Working Group of the American Association of Physicists in Medicine (AAPM), the European Society for Radiotherapy and Oncology (ESTRO), and the Australasian Brachytherapy Group (ABG) was created to aid in the transition from the AAPM TG-43 dose calculation formalism, the current standard, to model-based dose calculations. This work establishes the first test cases for low-energy photon-emitting brachytherapy using model-based dose calculation algorithms (MBDCAs). ACQUISITION AND VALIDATION METHODS: Five test cases are developed: (1) a single model 6711 125 I brachytherapy seed in water, 13 seeds (2) individually and (3) in combination in water, (4) the full Collaborative Ocular Melanoma Study (COMS) 16 mm eye plaque in water, and (5) the full plaque in a realistic eye phantom. Calculations are done with four Monte Carlo (MC) codes and a research version of a commercial treatment planning system (TPS). For all test cases, local agreement of MC codes was within ∼2.5% and global agreement was ∼2% (4% for test case 5). MC agreement was within expected uncertainties. Local agreement of TPS with MC was within 5% for test case 1 and ∼20% for test cases 4 and 5, and global agreement was within 0.4% for test case 1 and 10% for test cases 4 and 5. DATA FORMAT AND USAGE NOTES: Dose distributions for each set of MC and TPS calculations are available online (https://doi.org/10.52519/00005) along with input files and all other information necessary to repeat the calculations. POTENTIAL APPLICATIONS: These data can be used to support commissioning of MBDCAs for low-energy brachytherapy as recommended by TGs 186 and 221 and AAPM Report 372. This work additionally lays out a sample framework for the development of test cases that can be extended to other applications beyond eye plaque brachytherapy.

Phase II Trial of Five-Fraction Accelerated Partial Breast Irradiation (APBI) Using Noninvasive Image-Guided Breast Brachytherapy (NIBB).

PURPOSE/OBJECTIVE(S): NIBB has potential advantages over other APBI techniques by delivering highly conformal radiation with minimal collateral dose to the heart and lung compared with external beam techniques, but unlike other brachytherapy techniques NIBB is non-invasive. Previous data has shown encouraging outcomes using a 10-fraction regimen. To improve efficiency, convenience, and cost, reduction in the fraction number is desirable. Final results of a prospective phase II trial are reported. MATERIALS/METHODS: NIBB APBI was delivered using 28.5Gy in 5 fractions daily over 1 week. Patient eligibility criteria required: invasive carcinoma ≤2.0 cm or DCIS ≤3.0 cm, ER positive (if invasive), lymph node negative, LVI absent, and lumpectomy with margins negative by 2mm. The primary endpoint was grade ≥ 2 subcutaneous fibrosis/induration <30%. Secondary endpoints included any late toxicity, cosmetic outcome, and local control. RESULTS: 40 patients were treated with a median follow-up of 59.7 months. The mean age was 67 years (50-89 years) and tumor size was 1.0cm (0.3-2.0cm). 80% had invasive carcinoma. The mean breast separation with compression was 6.7cm (3.5-8.9cm). The 5-year actuarial local control was 96.6% and overall survival was 96.9%. Grade 2 and 3 late toxicities were 15% and 0%, respectively. The rate of grade 2 subcutaneous fibrosis/induration was 2.5% (+/-2.5%) meeting the study's primary endpoint. The most common late toxicity of any grade was skin telangiectasia; 22.5% grade 1 and 15% grade 2. Only breast separation was associated with telangiectasia risk, p=0.002. Overall cosmetic outcome was excellent, good, and fair/poor in 75%, 25%, and 0%, respectively. CONCLUSIONS: NIBB APBI delivered in 5 fractions results in a low rate of late toxicity and a high rate of good/excellent cosmetic outcomes. Telangiectasia risk can be minimized by keeping breast separation ≤7.0cm. The local failure rate was appropriately low. Further investigation of this technique is warranted.

AAPM WGDCAB Report 372: A joint AAPM, ESTRO, ABG, and ABS report on commissioning of model-based dose calculation algorithms in brachytherapy.

The introduction of model-based dose calculation algorithms (MBDCAs) in brachytherapy provides an opportunity for a more accurate dose calculation and opens the possibility for novel, innovative treatment modalities. The joint AAPM, ESTRO, and ABG Task Group 186 (TG-186) report provided guidance to early adopters. However, the commissioning aspect of these algorithms was described only in general terms with no quantitative goals. This report, from the Working Group on Model-Based Dose Calculation Algorithms in Brachytherapy, introduced a field-tested approach to MBDCA commissioning. It is based on a set of well-characterized test cases for which reference Monte Carlo (MC) and vendor-specific MBDCA dose distributions are available in a Digital Imaging and Communications in Medicine-Radiotherapy (DICOM-RT) format to the clinical users. The key elements of the TG-186 commissioning workflow are now described in detail, and quantitative goals are provided. This approach leverages the well-known Brachytherapy Source Registry jointly managed by the AAPM and the Imaging and Radiation Oncology Core (IROC) Houston Quality Assurance Center (with associated links at ESTRO) to provide open access to test cases as well as step-by-step user guides. While the current report is limited to the two most widely commercially available MBDCAs and only for 192 Ir-based afterloading brachytherapy at this time, this report establishes a general framework that can easily be extended to other brachytherapy MBDCAs and brachytherapy sources. The AAPM, ESTRO, ABG, and ABS recommend that clinical medical physicists implement the workflow presented in this report to validate both the basic and the advanced dose calculation features of their commercial MBDCAs. Recommendations are also given to vendors to integrate advanced analysis tools into their brachytherapy treatment planning system to facilitate extensive dose comparisons. The use of the test cases for research and educational purposes is further encouraged.

First clinical implementation of Yttrium-90 Disc Brachytherapy after FDA clearance.

PURPOSE: Herein, we study if high-dose-rate (HDR) yttrium-90 (90Y) brachytherapy could be utilized by medical physicists, radiation oncologists, and ophthalmic surgeons. METHODS AND MATERIALS: Yttrium-90 (90Y) beta-emitting brachytherapy sources received United States Food and Drug Administration clearance for episcleral treatment of ocular tumors and benign growths. Dose calibration traceable to the National Institute of Standards and Technology as well as treatment planning and target delineation methods were established. Single-use systems included a 90Y-disc affixed within specialized, multifunction, handheld applicator. Low-dose-rate to high-dose-rate prescription conversions and depth-dose determinations were performed. Radiation safety was evaluated based on live exposure rates during assembly and surgeries. Clinical data for radiation safety, treatment tolerability, and local control was collected. RESULTS: Practice parameters for the medical physicist, radiation oncologist, and ophthalmic surgeon were defined. Device sterilizations, calibrations, assemblies, surgical methods, and disposals were reproducible and effective. Treated tumors included iris melanoma, iridociliary melanoma, choroidal melanoma, and a locally invasive squamous carcinoma. Mean calculated 90Y disc activity was 14.33 mCi (range 8.8-16.6), prescription dose 27.8 Gy (range 22-30), delivered to depth of 2.3 mm (range 1.6-2.6), at treatment durations of 420 s (7.0 min, range 219 s-773 s). Both insertion and removal were performed during one surgical session. After surgery, each disc-applicator- system was contained for decay in storage. Treatments were well-tolerated. CONCLUSIONS: HDR 90Y episcleral brachytherapy devices were created, implementation methods developed, and treatments performed on 6 patients. Treatments were single-surgery, rapid, and well-tolerated with short-term follow up.

Brachytherapy evolution as seen today.

While brachytherapy is the oldest form of radiation therapy, it is also a very exciting field from both physics and clinical perspectives. From the physics standpoint, brachytherapy dosimetry is largely being governed by the inverse-square law, leading to an unparalleled dose deposition kernel (dose emitted by a seed or single dwell position), even compared to proton or heavy-ion beamlets. There is slightly more dose beyond the central deposition point, but comparatively very little prior to it, that is, little or no entrance dose! It is easy to sum multiple dwell positions that cover a tumor, and the intensity can be modulated quite effectively using dwell times. From a clinical perspective, what sets brachytherapy apart from other intraoperative modalities (e.g., laser, radiofrequency, cryogenic) is our ability to precisely calculate the energy deposited across the relevant patient geometry, anticipate the effect from known dose-outcome relationships, and deliver that energy with exquisite control and selectively to the target volume while sparing organs at risks. This targeting ability has improved substantially over the last two decades. It is built upon key foundational elements, many of which stem from the research and development within our medical physics community. This article provides an overview of these elements that combine to make brachytherapy a successful and developing radiotherapy modality.

GEC-ESTRO ACROP recommendations on calibration and traceability of HE HDR-PDR photon-emitting brachytherapy sources at the hospital level.

The vast majority of radiotherapy departments in Europe using brachytherapy (BT) perform temporary implants of high- or pulsed-dose rate (HDR-PDR) sources with photon energies higher than 50 keV. Such techniques are successfully applied to diverse pathologies and clinical scenarios. These recommendations are the result of Working Package 21 (WP-21) initiated within the BRAchytherapy PHYsics Quality Assurance System (BRAPHYQS) GEC-ESTRO working group with a focus on HDR-PDR source calibration. They provide guidance on the calibration of such sources, including practical aspects and issues not specifically accounted for in well-accepted societal recommendations, complementing the BRAPHYQS WP-18 Report dedicated to low energy BT photon emitting sources (seeds). The aim of this report is to provide a European-wide standard in HDR-PDR BT source calibration at the hospital level to maintain high quality patient treatments.

Recommendations for intraoperative mesh brachytherapy: Report of AAPM Task Group No. 222.

Mesh brachytherapy is a special type of a permanent brachytherapy implant: it uses low-energy radioactive seeds in an absorbable mesh that is sutured onto the tumor bed immediately after a surgical resection. This treatment offers low additional risk to the patient as the implant procedure is carried out as part of the tumor resection surgery. Mesh brachytherapy utilizes identification of the tumor bed through direct visual evaluation during surgery or medical imaging following surgery through radiographic imaging of radio-opaque markers within the sources located on the tumor bed. Thus, mesh brachytherapy is customizable for individual patients. Mesh brachytherapy is an intraoperative procedure involving mesh implantation and potentially real-time treatment planning while the patient is under general anesthesia. The procedure is multidisciplinary and requires the complex coordination of multiple medical specialties. The preimplant dosimetry calculation can be performed days beforehand or expediently in the operating room with the use of lookup tables. In this report, the guidelines of American Association of Physicists in Medicine (AAPM) are presented on the physics aspects of mesh brachytherapy. It describes the selection of radioactive sources, design and preparation of the mesh, preimplant treatment planning using a Task Group (TG) 43-based lookup table, and postimplant dosimetric evaluation using the TG-43 formalism or advanced algorithms. It introduces quality metrics for the mesh implant and presents an example of a risk analysis based on the AAPM TG-100 report. Recommendations include that the preimplant treatment plan be based upon the TG-43 dose calculation formalism with the point source approximation, and the postimplant dosimetric evaluation be performed by using either the TG-43 approach, or preferably the newer model-based algorithms (viz., TG-186 report) if available to account for effects of material heterogeneities. To comply with the written directive and regulations governing the medical use of radionuclides, this report recommends that the prescription and written directive be based upon the implanted source strength, not target-volume dose coverage. The dose delivered by mesh implants can vary and depends upon multiple factors, such as postsurgery recovery and distortions in the implant shape over time. For the sake of consistency necessary for outcome analysis, prescriptions based on the lookup table (with selection of the intended dose, depth, and treatment area) are recommended, but the use of more advanced techniques that can account for real situations, such as material heterogeneities, implant geometric perturbations, and changes in source orientations, is encouraged in the dosimetric evaluation. The clinical workflow, logistics, and precautions are also presented.

Source strength determination in iridium-192 and cobalt-60 brachytherapy: A European survey on the level of agreement between clinical measurements and manufacturer certificates.

BACKGROUND AND PURPOSE: Brachytherapy treatment outcomes depend on the accuracy of the delivered dose distribution, which is proportional to the reference air-kerma rate (RAKR). Current societal recommendations require the medical physicist to compare the measured RAKR values to the manufacturer source calibration certificate. The purpose of this work was to report agreement observed in current clinical practice in the European Union. MATERIALS AND METHODS: A European survey was performed for high- and pulsed-dose-rate (HDR and PDR) high-energy sources (192Ir and 60Co), to quantify observed RAKR differences. Medical physicists at eighteen hospitals from eight European countries were contacted, providing 1,032 data points from 2001 to 2020. RESULTS: Over the survey period, 77% of the 192Ir measurements used a well chamber instead of the older Krieger phantom method. Mean differences with the manufacturer calibration certificate were 0.01% ± 1.15% for 192Ir and -0.1% ± 1.3% for 60Co. Over 95% of RAKR measurements in the clinic were within 3% of the manufacturer calibration certificate. CONCLUSIONS: This study showed that the agreement level was generally better than that reflected in prior societal recommendations positing 5%. Future recommendations on high-energy HDR and PDR source calibrations in the clinic may consider tightened agreements levels.

Initial Clinical Experience With Novel Directional Low-Dose Rate Brachytherapy for Retroperitoneal Sarcoma.

BACKGROUND: A novel Palladium-103 low-dose rate (LDR) brachytherapy device was developed to provide dose-escalation to the tumor bed after resection while shielding adjacent tissues. This multicenter report describes the initial experience with this device in patients with retroperitoneal sarcoma (RPS). MATERIALS AND METHODS: Patients with recurrent RPS, prior radiotherapy, and/or concern for positive margins were considered. An LDR brachytherapy dose of 20-60 Gy was administered, corresponding to biologically effective dose values of 15-53 Gy and equivalent dose values of 12-43 Gy. RESULTS: Six patients underwent implantation at four institutions. Of these, five had recurrent disease in the retroperitoneum or pelvic sidewall, one had untreated locally advanced leiomyosarcoma, two had prior external beam radiation therapy at the time of initial diagnosis, and four received neoadjuvant external beam radiation therapy plus brachytherapy. The device was easily implanted and conformed to the treatment area. Median follow-up was 16 mo; radiation was delivered to the at-risk margin with minimal irradiation of adjacent structures. No local recurrences at the site of implantation, device migration, or radiation-related toxicities were observed. CONCLUSIONS: The novel LDR directional brachytherapy device successfully delivered a targeted dose escalation to treat RPS high-risk margins. Lack of radiation-related toxicity demonstrates its safety.

Quantifying risk using FMEA: An alternate approach to AAPM TG-100 for scoring failures and evaluating clinical workflow.

PURPOSE: Renovation of the brachytherapy program at a leading cancer center utilized methods of the AAPM TG-100 report to objectively evaluate current clinical brachytherapy workflows and develop techniques for minimizing the risk of failures, increasing efficiency, and consequently providing opportunities for improved treatment quality. The TG-100 report guides evaluation of clinical workflows with recommendations for identifying potential failure modes (FM) and scoring them from the perspective of their occurrence frequency O, failure severity S, and inability to detect them D. The current study assessed the impact of differing methods to determine the risk priority number (RPN) beyond simple multiplication. METHODS AND MATERIALS: The clinical workflow for a complex brachytherapy procedure was evaluated by a team of 15 staff members, who identified discrete FM using alternate scoring scales than those presented in the TG-100 report. These scales were expanded over all clinically relevant possibilities with care to emphasize mitigation of natural bias for scoring near the median range as well as to enhance the overall scoring-system sensitivity. Based on staff member perceptions, a more realistic measure of risk was determined using weighted functions of their scores. RESULTS: This new method expanded the range of RPN possibilities by a factor of 86, improving evaluation and recognition of safe and efficient clinical workflows. Mean RPN values for each FM decreased by 44% when changing from the old to the new clinical workflow, as evaluated using the TG-100 method. This decreased by 66% when evaluated with the new method. As a measure of the total risk associated with an entire clinical workflow, the integral of RPN values increased by 15% and decreased by 31% with the TG-100 and new methods, respectively. CONCLUSIONS: This appears to be the first application of an alternate approach to the TG-100 method for evaluating the risk of clinical workflows. It exemplifies the risk analysis techniques necessary to rapidly evaluate simple clinical workflows appropriately.

Recommendations on the practice of calibration, dosimetry, and quality assurance for gamma stereotactic radiosurgery: Report of AAPM Task Group 178.

The American Association of Physicists in Medicine (AAPM) formed Task Group 178 (TG-178) to perform the following tasks: review in-phantom and in-air calibration protocols for gamma stereotactic radiosurgery (GSR), suggest a dose rate calibration protocol that can be successfully utilized with all gamma stereotactic radiosurgery (GSR) devices, and update quality assurance (QA) protocols in TG-42 (AAPM Report 54, 1995) for static GSR devices. The TG-178 report recommends a GSR dose rate calibration formalism and provides tabulated data to implement it for ionization chambers commonly used in GSR dosimetry. The report also describes routine mechanical, dosimetric, and safety checks for GSR devices, and provides treatment process quality assurance recommendations. Sample worksheets, checklists, and practical suggestions regarding some QA procedures are given in appendices. The overall goal of the report is to make recommendations that help standardize GSR physics practices and promote the safe implementation of GSR technologies.

A study of Type B uncertainties associated with the photoelectric effect in low-energy Monte Carlo simulations.

Purpose.To estimate Type B uncertainties in absorbed-dose calculations arising from the different implementations in current state-of-the-art Monte Carlo (MC) codes of low-energy photon cross-sections (<200 keV).Methods.MC simulations are carried out using three codes widely used in the low-energy domain: PENELOPE-2018, EGSnrc, and MCNP. Three dosimetry-relevant quantities are considered: mass energy-absorption coefficients for water, air, graphite, and their respective ratios; absorbed dose; and photon-fluence spectra. The absorbed dose and the photon-fluence spectra are scored in a spherical water phantom of 15 cm radius. Benchmark simulations using similar cross-sections have been performed. The differences observed between these quantities when different cross-sections are considered are taken to be a good estimator for the corresponding Type B uncertainties.Results.A conservative Type B uncertainty for the absorbed dose (k = 2) of 1.2%-1.7% (<50 keV), 0.6%-1.2% (50-100 keV), and 0.3% (100-200 keV) is estimated. The photon-fluence spectrum does not present clinically relevant differences that merit considering additional Type B uncertainties except for energies below 25 keV, where a Type B uncertainty of 0.5% is obtained. Below 30 keV, mass energy-absorption coefficients show Type B uncertainties (k = 2) of about 1.5% (water and air), and 2% (graphite), diminishing in all materials for larger energies and reaching values about 1% (40-50 keV) and 0.5% (50-75 keV). With respect to their ratios, the only significant Type B uncertainties are observed in the case of the water-to-graphite ratio for energies below 30 keV, being about 0.7% (k = 2).Conclusions.In contrast with the intermediate (about 500 keV) or high (about 1 MeV) energy domains, Type B uncertainties due to the different cross-sections implementation cannot be considered subdominant with respect to Type A uncertainties or even to other sources of Type B uncertainties (tally volume averaging, manufacturing tolerances, etc). Therefore, the values reported here should be accommodated within the uncertainty budget in low-energy photon dosimetry studies.

Surface brachytherapy: Joint report of the AAPM and the GEC-ESTRO Task Group No. 253.

The surface brachytherapy Task Group report number 253 discusses the common treatment modalities and applicators typically used to treat lesions on the body surface. Details of commissioning and calibration of the applicators and systems are discussed and examples are given for a risk-based analysis approach to the quality assurance measures that are necessary to consider when establishing a surface brachytherapy program.

Novel and programmatic improvements to the workflow associated with the AccuBoost breast brachytherapy procedure.

PURPOSE: While the noninvasive breast brachytherapy (NIBB) treatment procedure, known as AccuBoost, for breast cancer patients is well established, the treatment quality can be improved by the efficiency of the workflow delivery. A formalized approach evaluated the current workflow through failure modes and effects analysis and generated insight for developing new procedural workflow techniques to improve the clinical treatment process. METHODS AND MATERIALS: AccuBoost treatments were observed for several months while gathering details on the multidisciplinary workflow. A list of possible failure modes for each procedure step was generated and organized by timing within the treatment process. A team of medical professionals highlighted procedural steps that unnecessarily increased treatment time, as well as introduced quality deficiencies involving applicator setup, treatment planning, and quality control checks preceding brachytherapy delivery. Procedural improvements and their impact on the clinical workflow are discussed. RESULTS: The revised clinical workflow included the following key procedural enhancements. Prepatient arrival: Improvement of prearrival preparation requires advance completion of dose calculation documentation with patient-specific setup data. Patient arrival pretreatment: Physicists carry out dwell time calculations and check the plan, while the therapist concurrently performs several checks of the ensuing hardware configuration. TREATMENT: An electronic method to export the associated HDR brachytherapy paperwork to the electronic medical record system with electronic signatures and captured approvals was generated. Posttreatment: The therapist confirms the applicators were appropriately positioned, and treatment was delivered as expected. CONCLUSIONS: The procedural improvements reduced the overall treatment time, improved consistency across users, and eased performance of this special procedure for all participants.

Dose-rate considerations for the INTRABEAM electronic brachytherapy system: Report from the American association of physicists in medicine task group no. 292.

The purpose of this report is to provide detailed guidance on the dosimetry of the INTRABEAM® (Carl Zeiss Medical AG, Jena, Germany) electronic brachytherapy (eBT) system as it stands at the present time. This report has been developed by the members of American Association of Physicists in Medicine (AAPM) Task Group 292 and endorsed by the AAPM. Members of AAPM Task Group 292 on Electronic-Brachytherapy Dosimetry have reviewed pertinent publications and user manuals regarding the INTRABEAM system dosimetry and manufacturer-supplied dose calculation protocols. Formal written correspondence with Zeiss has also provided further clarification. Dose-rate calculations for the INTRABEAM system are highly dependent on choice of dosimetry protocol. Even with careful protocol selection, large uncertainties remain due to the incomplete characterization of the ionization chambers used for verification with respect to their energy dependence as well as manufacturing variations. There are two distinct sets of dose-rate data provided by Zeiss for the INTRABEAM system. One dataset (Calibration V4.0) is representative of the physical dose surrounding the source and the other dataset (TARGIT) has been adjusted to be consistent with a clinical trial named TARGIT (TARGeted Intraoperative RadioTherapy). The adjusted TARGIT doses are quite dissimilar to the physical doses, with differences ranging from 14% to 30% at the surface of a spherical applicator, depending on its diameter, and up to a factor of two at closer distances with the smaller needle applicators. In addition, ion chamber selection and associated manufacturing tolerances contribute to significant additional uncertainties. With these substantial differences in dose rates and their associated uncertainties, it is important for users to be aware of how each value is calculated and whether it is appropriate to be used for the intended treatment. If users intend to deliver doses that are the same as they were in 1998 at the onset of the TARGIT trial, then the TARGIT dose-rate tables should be used. The Calibration V4.0 dose rates may be more appropriate to use for applications other than TARGIT trial treatments, since they more closely represent the physical doses being delivered. Users should also be aware of the substantial uncertainties associated with the provided dose rates, which are due to beam hardening, chamber geometry, and selection of the point-of-measurement for a given ionization chamber. This report serves to describe the details and implications of the manufacturer-recommended dosimetry formalism for users of the INTRABEAM system.

Electronic intracavitary brachytherapy quality management based on risk analysis: The report of AAPM TG 182.

PURPOSE: The purpose of this study was to provide guidance on quality management for electronic brachytherapy. MATERIALS AND METHODS: The task group used the risk-assessment approach of Task Group 100 of the American Association of Physicists in Medicine. Because the quality management program for a device is intimately tied to the procedure in which it is used, the task group first designed quality interventions for intracavitary brachytherapy for both commercial electronic brachytherapy units in the setting of accelerated partial-breast irradiation. To demonstrate the methodology to extend an existing risk analysis for a different application, the task group modified the analysis for the case of post-hysterectomy, vaginal cuff irradiation for one of the devices. RESULTS: The analysis illustrated how the TG-100 methodology can lead to interventions to reduce risks and improve quality for each unit and procedure addressed. CONCLUSION: This report provides a model to guide facilities establishing a quality management program for electronic brachytherapy.

Model-Based Dose Calculation Algorithms for Brachytherapy Dosimetry.

The purpose of this study was to review the limitations of dose calculation formalisms for photon-emitting brachytherapy sources based on the American Association of Physicists in Medicine (AAPM) Task Group No. 43 (TG-43) report and to provide recommendations to transition to model-based dose calculation algorithms. Additionally, an overview of these algorithms and approaches is presented. The influence of tissue and seed/applicator heterogeneities on brachytherapy dose distributions for breast, gynecologic, head and neck, rectum, and prostate cancers as well as eye plaques and electronic brachytherapy treatments were investigated by comparing dose calculations based on the TG-43 formalism and model-based dose calculation algorithms.

Automated position and size selection of round applicators for AccuBoost breast brachytherapy.

PURPOSE: AccuBoost is a complex non-invasive brachytherapy procedure for breast treatment. This technique requires a radiation oncologist to manually select applicator grid position and size by overlaying transparencies over a mammographic image to encompass surgical clips and resected tumor bed. An algorithm was developed in MATLAB™ to automate the selection of round applicators based on surgical clip position. MATERIAL AND METHODS: A total of 42 mammograms belonging to 10 patients were retrospectively analyzed. Images were pre-processed by masking imprinted localization grid and regions around the grid. A threshold was applied to isolate high-intensity pixels and generate a binary image. A set of morphological operations including region dilation, filling, clearing border structures, and erosion were performed to segment the different regions. A support vector machine classification model was trained to categorize segmented regions as either surgical clips or miscellaneous objects based on different region properties (area, perimeter, eccentricity, circularity, minor axis length, and intensity-derived quantities). Applicator center position was determined by calculating the centroid of detected clips. Size of the applicator was determined with the smallest circle that encompassed all clips with an isotropic 1.0 cm margin. RESULTS: The clip identification model classified 946 regions, with a sensitivity of 96.6% and a specificity of 98.2%. Applicator position was correctly predicted for 20 of 42 fractions and was within 0.5 cm of physician-selected position for 33 of 42 fractions. Applicator size was correctly predicted for 25 out of 42 fractions. CONCLUSIONS: The proposed algorithm provided a method to quantitatively determine applicator position and size for AccuBoost treatments, and may serve as a tool for independent verifications. The discrepancy between physician-selected and algorithm-predicted determinations of applicator position and size suggests that the methodology may be further improved by considering radiomic features of breast tissue in addition to clip position.