Brachytherapy Treatment Planning Research Articles

Comprehensive commissioning of a cone beam CT imaging ring for treatment of HDR GYN patients

PurposeA new mobile cone beam computed tomography (CBCT) imaging ring (IRm, Elekta, v2.10.6, Veenendaal, Netherlands) has recently been proposed for brachytherapy to improve procedure efficiency. We describe the commissioning process and end-to-end tests for GYN HDR brachytherapy employing IRm CBCT imaging. Materials and MethodsCommissioning included imaging isocenter test, 3D image quality, 2D imaging quality, image dose, and tube characteristics. CIRS HDR GYN phantom and Venezia CT/MR gynecological applicator were used to perform end-to-end (E2E) tests and optimize workflow. Venezia applicator and four interstitial needles were inserted into the phantom and IRm CBCT images were acquired. Phantom and applicator were scanned with CT scanner (Siemens SOMATOM go.Open Pro) using department's pelvis imaging protocol. MR imaging was performed using 0.35T MR Linac TRUFI pulse sequence. CBCT images were registered to CT and MR using rigid registration to assess image quality and applicator geometry fidelity. ResultsAll physics tests passed within acceptance tolerances. Registration of CBCT images to MR and CT scans was acceptable for applicator placement. Applicator registration of CBCT images to CT demonstrated excellent agreement of most distal source dwell position (<1 mm). Slice thickness was also measured to be 1.25 mm, within 0.5 mm of its nominal value. ConclusionBased on E2E and commissioning results, IRm is an appropriate tool for brachytherapy treatment planning. This study demonstrated good image quality in GYN phantom and Venezia applicator using the IRm. Distal source dwell position agreement between CBCT and CT was acceptable for clinical use.

Assessment of Organ Motion Impact on Brachytherapy Treatment Planning of Cervix Cancer

To quantify dosimetrically the impact of intra-fractional organs movements during brachytherapy treatment of cervix cancer (CC).

Methodology for integrating MCNP6 Monte Carlo simulation into PLUNC for prostate brachytherapy planning

Brachytherapy is a well-established therapeutic technique for treating tumours involving the placement of radioactive encapsulated sources close to or in direct contact with a tumour. Considering this type of treatments, the purpose of this work is to incorporate Monte Carlo (MC) simulation into brachytherapy treatment planning. This approach allows for precise estimation of dose distribution in target organs as well as in Organs At Risk (OAR), due to the accuracy of the MC methods in describing dose deposition.To carry out this work, the medical image visualization and dose analysis tools provided by the open-source planner PlanUNC (PLUNC) were utilized. Additionally, a set of programs was developed which automatize the main steps of a treatment planning segmentation, from DICOM images, exporting geometries determining materials and seeds positions, creating an input file for the simulation code (MCNP6.2) and, finally, reading and visualization of the simulation results in the format of the used planning software. With this methodology, results of 3D dose distribution, isodoses curves, Dose-Volume Histograms (DVH), and absorbed dose in OAR were obtained. Thus, the integration of the MC simulation into PLUNC for brachytherapy treatments, has demonstrate its utility for this purpose, showing adaptability to different anatomical geometries and extensibility to various types of treatments.

The care and management of patients with indication for intracavitary 3D brachytherapy

This paper evaluates the differences between two types of normalization of 3D intracavitary brachytherapy (3D-BT) treatment plans for malignant cervical lesions. Immediately after the end of the treatment, intracavitary irradiation was continued, three fractions with 7.5 Gy per session, using High Dose Rate (HDR) brachytherapy and 3D imaging. Tree plans were made, one for the 3 cm diameter vaginal applicator and two for the vaginal applications where 2.6 cm diameter intracavitary applicators were used. Treatment plans were made using the dedicated software Eclipse-BrachyVision version 10.0.42, manufacturer Varian Medical Systems. Dose Calculation Model-Linear source and step size 0.50 cm. The normalization was done in the first phase at the surface of the applicator, at the prescription line. The next normalization was by volume. We present the results of the two normalizations. The data obtained from the 2 normalization methods was entered into an Excel spreadsheet. We took into account the dose prescribed for EBRT, the number of fractions, the dose/fr, the dose prescribed for 3D-BT and the dose absorbed by the OAR in 2 cm. We also took into account the isodose obtained for 90%, 100% and 150% of the volume of interest. In the first optimization, the absorbed dose was between 7.45–8 Gy. We also tracked BED and EQD2 in the spreadsheet. Results: In the second optimization, on the target volume, we obtained for the plan with a cylinder with a diameter of 3 cm (Ф = 3 cm), 90% of the IR volume the dose of 7.5 Gy. For Ф = 2.6 cm, of the IR volume with a dose of 7.5 Gy and for the last plane also with Ф = 2.6 cm, of the IR2 volume with a dose of 7.5 Gy. Calculated data for EQD2 in the three planes with normalization to the line on the applicator surface resulted in higher doses for OARs compared to EQD2 data from volume optimization. The volume of interest according to EQD2 calculations in the first optimization had 77.8 Gy and in the second optimization it had 78.4 Gy. After volume optimization, we achieved 78.4 Gy for all three brachytherapy fractions and the 25 EBRT fractions, the rectum totaling a dose of 67.1 Gy and the bladder 77.5 Gy. With the volume-optimized plans, we obtained a coverage between V90% = D100%.

Practical experience with initial quality assurance of a high dose rate brachytherapy grid-based Boltzmann solver algorithm.

The purpose of this study was to validate the use of a model-based dose calculation algorithm (MBDCA), Acuros BV, for high dose rate brachytherapy treatment planning for a community-based hospital with a Bravos afterloader. Based on published AAPM recommendations, this work details a practical approach for community-based clinics to complete initial validation of Acuros BV, in order to add a MBDCA to a TG-43 based brachytherapy treatment planning program. Source dimensions and materials used in Acuros BV and TG-43 source models were compared to the physical source. TG-186 testing was completed with standardized test cases externally calculated with Monte Carlo compared to locally calculated with Acuros BV. Point doses calculated using TG-43 were compared to those calculated with Acuros BV in water at various dose grid settings. Secondary dose check software was used to evaluate dose distributions resembling clinical patient plans, both in water and on CT datasets representative of patient anatomy. The major source of discrepancy of source models was the length of modeled steel cable. TG-186 testing showed that the largest differences between Monte Carlo and Acuros BV dose distributions were located along the source axis for cases calculated in water, as well as located in regions of high dose gradients and within the applicator for the case calculated with a generic shielded applicator. An audit of point doses calculated with both TG-43 and Acuros BV in water found that dose grid settings significantly affected agreement. Secondary dose check software indicated that Acuros BV functioned satisfactorily, and a 5% threshold was adopted for secondary dose checks on gynecologic plans. This validation process indicated that Acuros BV met expected standards and affirmed its suitability for integration into this clinical practice's brachytherapy treatment planning.

AAPM Task Group Report 267: A joint AAPM GEC-ESTRO report on biophysical models and tools for the planning and evaluation of brachytherapy.

Brachytherapy utilizes a multitude of radioactive sources and treatment techniques that often exhibit widely different spatial and temporal dose delivery patterns. Biophysical models, capable of modeling the key interacting effects of dose delivery patterns with the underlying cellular processes of the irradiated tissues, can be a potentially useful tool for elucidating the radiobiological effects of complex brachytherapy dose delivery patterns and for comparing their relative clinical effectiveness. While the biophysical models have been used largely in research settings by experts, it has also been used increasingly by clinical medical physicists over the last two decades. A good understanding of the potentials and limitations of the biophysical models and their intended use is critically important in the widespread use of these models. To facilitate meaningful and consistent use of biophysical models in brachytherapy, Task Group 267 (TG-267) was formed jointly with the American Association of Physics in Medicine (AAPM) and The Groupe Européen de Curiethérapie and the European Society for Radiotherapy & Oncology (GEC-ESTRO) to review the existing biophysical models, model parameters, and their use in selected brachytherapy modalities and to develop practice guidelines for clinical medical physicists regarding the selection, use, and interpretation of biophysical models. The report provides an overview of the clinical background and the rationale for the development of biophysical models in radiation oncology and, particularly, in brachytherapy; a summary of the results of literature review of the existing biophysical models that have been used in brachytherapy; a focused discussion of the applications of relevant biophysical models for five selected brachytherapy modalities; and the task group recommendations on the use, reporting, and implementation of biophysical models for brachytherapy treatment planning and evaluation. The report concludes with discussions on the challenges and opportunities in using biophysical models for brachytherapy and with an outlook for future developments.

Dosimetric benefits and preclinical performance of steerable needles in HDR prostate brachytherapy

Prostate cancer patients with an enlarged prostate and/or excessive pubic arch interference (PAI) are generally considered non-eligible for high-dose-rate (HDR) brachytherapy (BT). Steerable needles have been developed to make these patients eligible again. This study aims to validate the dosimetric impact and performance of steerable needles within the conventional clinical setting.HDR BT treatment plans were generated, needle implantations were performed in a prostate phantom, with prostate volume > 55 cm3 and excessive PAI of 10 mm, and pre- and post-implant dosimetry were compared considering the dosimetric constraints: prostate V100 > 95 % (13.50 Gy), urethra D0.1cm3 < 115 % (15.53 Gy) and rectum D1cm3 < 75 % (10.13 Gy).The inclusion of steerable needles resulted in a notable enhancement of the dose distribution and prostate V100 compared to treatment plans exclusively employing rigid needles to address PAI. Furthermore, the steerable needle plan demonstrated better agreement between pre- and post-implant dosimetry (prostate V100: 96.24 % vs. 93.74 %) compared to the rigid needle plans (79.13 % vs. 72.86 % and 87.70 % vs. 81.76 %), with no major changes in the clinical workflow and no changes in the clinical set-up.The steerable needle approach allows for more flexibility in needle positioning, ensuring a highly conformal dose distribution, and hence, HDR BT is a feasible treatment option again for prostate cancer patients with an enlarged prostate and/or excessive PAI.

Dosimetric Comparison of Inverse Planning Simulated Annealing and Manual Optimization for Intracavitary Cervix Brachytherapy

Background/Aims: Different optimization methods in brachytherapy treatment planning is used. The aim of this study is to evaluate dosimetric differences between manual optimization (MO) and inverse planning simulated annealing (IPSA) planning techniques commonly used in brachytherapy of cervical cancer. Methods: Fifteen cervical cancer patients were included in this study. Nucletron standard tandem-ovoid (TO) applicators were used for treatment. High-risk clinical tumor volume (HR-CTV), bladder, rectum, and sigmoid contouring were performed according to GEC-ESTRO recommendations. Two plans were created for each patient using IPSA and MO techniques. While a dose of 700 cGy was prescribed to the target volume during the planning phase, an effort was made to protect the organs at risk in the best way possible. IPSA and MO planning techniques were compared via dose volume histogram (DVH). Results: There was no significant difference between HR-CTV and CI values for MO and IPSA techniques. There was a significant difference between IPSA and MO techniques for the 2cm3 volume of the rectum (p= 0.002). It was observed that the bladder was better protected by the IPSA technique. There was a 6.26% dose difference between IPSA and MO for the bladder. A significant difference was found between IPSA and MO techniques for the 2cm3 volume of the sigmoid (p= 0.002). The IPSA technique was superior to the MO technique in terms of time. Conclusions: The IPSA technique was superior to the MO technique in terms of protecting organs at risk (OARs). IPSA provides a faster and higher quality plan in cervical brachytherapy.

RapidBrachyTG43: A Geant4-based TG-43 parameter and dose calculation module for brachytherapy dosimetry.

The AAPM TG-43U1 formalism remains the clinical standard for dosimetry of low- and high-energy -emitting brachytherapy sources. TG-43U1 and related reports provide consensus datasets of TG-43 parameters derived from various published measured data and Monte Carlo simulations. These data are used to perform standardized and fast dose calculations for brachytherapy treatmentplanning. Monte Carlo TG-43 dosimetry parameters are commonly derived to characterize novel brachytherapy sources. RapidBrachyTG43 is a module of RapidBrachyMCTPS, a Monte Carlo-based treatment planning system, designed to automate this process, requiring minimal user input to prepare Geant4-based Monte Carlo simulations for a source. RapidBrachyTG43 may also perform a TG-43 dose to water-in-water calculation for a plan, substantially accelerating the same calculation performed using RapidBrachyMCTPS's Monte Carlo dose calculationengine. TG-43 parameters , , , and were calculated using three commercial source models, one each of I, Ir, and Co, and were benchmarked to published data. TG-43 dose to water was calculated for a clinical breast brachytherapy plan and was compared to a Monte Carlo dose calculation with all patient tissues, air, and catheters set towater. TG-43 parameters for the three simulated sources agreed with benchmark datasets within tolerances specified by the High Energy Brachytherapy Dosimetry working group. A gamma index comparison between the TG-43 and Monte Carlo dose-to-water calculations with a dose difference and difference to agreement criterion of 1%/1 mm yielded a 98.9% pass rate, with all relevant dose volume histogram metrics for the plan agreeing within 1%. Performing a TG-43-based dose calculation provided an acceleration of dose-to-water calculation by a factor of165. Determination of TG-43 parameter data for novel brachytherapy sources may now be facilitated by RapidBrachyMCTPS. These parameter datasets and existing consensus or published datasets may also be used to determine the TG-43 dose for a plan inRapidBrachyMCTPS.

A comparison of TG-43 and TG-186 dose calculation algorithms for treatment planning of intra-cavitary brachytherapy using tandem and ovoid applicator

A comparison of TG-43 and TG-186 dose calculation algorithms for treatment planning of intra-cavitary brachytherapy using tandem and ovoid applicator

Glossary of Terms and Concepts in Medical Radiation Physics. Terminology Used in Dosimetry and Treatment Planning of Brachytherapy

Medical radiation physics supports medical diagnostic and treatment process based on the use of ionizing radiation in radiation therapy, nuclear medicine, radiation diagnostics and radiation safety of patients and personnel. However, the successful implementation of this process requires close interaction of specialists in all the above areas. The basis of such interaction is the unification of the terminology and concepts used at various stages of the diagnostic and treatment process. The article presents a glossary on dosimetry and treatment planning of brachytherapy which contains the most commonly used terms in this field and explanations for each of them. The glossary is intended for use both in professional education, including postgraduate education, and for medical physicists and radiation oncologists working in radiological medical organizations

Prospective Evaluation of Automated Contouring for CT-Based Brachytherapy for Gynecologic Malignancies

PurposeThe use of deep learning to auto-contour organs-at-risk (OARs) in gynecologic radiation treatment is well-established. Yet, there is limited data investigating the prospective use of auto-contouring in clinical practice. In this study, we assess the accuracy and efficiency of auto-contouring OARs for CT-based brachytherapy treatment planning of gynecologic malignancies. Materials and MethodsAn in-house contouring tool automatically delineated five OARs in gynecologic radiation treatment planning: the bladder, small bowel, sigmoid, rectum, and urethra. Accuracy of each auto-contour was evaluated using a 5-point Likert scale: a score of five indicated the contour could be used without edits, while a score of one indicated the contour was unusable. During scoring, automated contours were edited and subsequently used for treatment planning. Dice similarity coefficient (DSC), mean surface distance (MSD), 95% Hausdorff Distance (95HD), Hausdorff Distance (HD), and dosimetric changes between original and edited contours were calculated. Contour approval time and total planning time of a prospective auto-contoured (AC) cohort were compared to times from a retrospective manually contoured (MC) cohort. ResultsThirty AC cases from January 2022 to July 2022 and thirty-one MC cases from July 2021 to January 2022 were included. The mean (±SD) Likert score for each OAR was the following: bladder 4.77 (±0.58), small bowel 3.96 (±0.91), sigmoid colon 3.92 (±0.81), rectum 4.6 (±0.71), and urethra 4.27 (±0.78). No auto-contours required major edits. All OARs had a mean DSC > 0.86, MSD < 0.48mm, 95HD < 3.2mm, and HD < 10.32mm between original and edited contours. There was no significant difference in DVH metrics (D2.0cc/D0.1cc) between original and edited contours (p-values > 0.05). The average time to plan approval in the AC cohort was 19% less than the MC cohort. (AC vs. MC, 117.0 + 18.0 minutes versus 144.9 ± 64.5 minutes, p=0.045). ConclusionsAutomated contouring is useful and accurate in clinical practice. Auto-contouring OARs streamlines radiation treatment workflows and decreases time required to design and approve gynecologic brachytherapy plans.

A robust evaluation of 49 high-dose-rate prostate brachytherapy treatment plans including all major uncertainties.

Uncertainties in radiotherapy cause deviation from the planned dose distribution and may result in delivering a treatment that fails to meet clinical objectives. The impact of uncertainties is unique to the patient anatomy and the needle locations in HDR prostate brachytherapy. Evaluating this impact during treatment planning is not common practice, relying on margins around the target or organs-at-risk to account for uncertainties. A robust evaluation framework for HDR prostate brachytherapy treatment plans was evaluated on 49 patient plans, measuring the range of possible dosimetric outcomes to the patient due to 14 major uncertainties. Patient plans were evaluated for their robustness to uncertainties by simulating probable uncertainty scenarios. Five-thousand probabilistic and 1943 worst-case scenarios per patient were simulated by changing the position and size of structures and length of dwell times from their nominal values. For each uncertainty scenario, the prostate D90 and maximum doses to the urethra, D0.01cc , and rectum, D0.1cc , were calculated. The D90 was an average 1.16±0.51% (mean±SD) below nominal values for the probabilistic scenarios; the D0.01cc metric was 2.24±0.90% higher; and D0.1cc was greater by 0.48±0.30%. The D0.01cc and D90 metrics were more sensitive to uncertainties than D0.1cc , with a median of 79.0% and 84.9% of probabilistic scenarios passing the constraints, compared to 96.5%. The median pass-rate for scenarios that passed all three metrics simultaneously was 63.4%. Assessing treatment plan robustness improves plan quality assurance, is achievable in less than 1-min, and identifies treatment plans with poor robustness, allowing re-optimization before delivery.

Total Reference Air Kerma (TRAK) is Associated with Dosimetric Parameters in Template-Based High Dose-Rate (HDR) Interstitial Brachytherapy in Advanced Gynecologic Cancers

To study TRAK and its association with dosimetric parameters in template-based high dose-rate interstitial brachytherapy in advanced gynecologic cancers. Brachytherapy treatment plans of 53 patients treated between 2012 and 2022 at our institution with template-based Iridium-192 HDR brachytherapy, post-external beam RT, for locally advanced cancers of the cervix and vagina were retrospectively reviewed. Brachytherapy dose ranged from 25 to 30-Gy delivered in 4 to 6 fractions. The median number of flexi-guide catheters implanted was 18 (range 10-30). Clinical Target Volume (CTV) values were mean (±SD): 72.2 (±40.4) cm3 (high-risk, HR) and 182.2 (±73.7) cm3 (intermediate-risk, IR) respectively. TRAK per fraction (cGy at 1m), dose-volume information for the implant, target, and organ-at-risk (OAR) were recorded. Indices for dose coverage (CI), homogeneity (DHI), non-uniformity (DNR), overdose volume (ODI) were computed. Regression and correlation tests were used to study the TRAK relationship with various dosimetric parameters. The false discovery rate at a 5% level was corrected using the Benjamini-Hochberg procedure. The average TRAK per fraction was 0.365 (±0.12) cGy. Mean and range values of plan quality indices were - CI 0.92 (0.7- 1.0), DHI 0.57 (0.41 - 0.77), DNR 0.43 (0.23 - 0.59) and ODI 0.22 (0.11 - 0.38), respectively Correlation results for TRAK with various dosimetric indices are presented in Table 1. TRAK showed a weak correlation with the number of flexi-guide catheters implanted (r = 0.35, p = 0.013). TRAK correlated strongly with target volumes (CTV_HR and CTV_IR and CTV_HR V100%) and with isodose volumes at both high (V300, V200, V150), and low dose levels (V90, V85, V50) (p<0.00001). TRAK correlated moderately with OAR 2-cm3 doses (p<0.00001). A weak correlation was observed between TRAK and plan quality indices. TRAK correlates positively with target volume and volumes enclosed by isodoses at various dose levels in interstitial HDR brachytherapy of advanced Gynecologic Cancers. Interestingly, our study observed a comparatively stronger positive correlation between TRAK and Sigmoid 2-cm3 dose, equated to TRAK correlation with bladder, rectum, and small bowel 2-cm3 doses. This finding could interest future studies utilizing TRAK as a surrogate for treatment outcome and toxicity.

MRI-Guided High-Dose-Rate Gynecologic Brachytherapy Using an MR-Linac as an MR Simulator: A Single Institutional Experience

The goal of this study was to commission the use of a magnetic resonance linear accelerator (MR-linac; Unity) for imaging of gynecologic high-dose-rate (HDR) brachytherapy. This included optimizing imaging protocols and workflow development. T1-weighted and T2-weighted HDR imaging protocols were optimized on the Unity for HDR gynecologic imaging and treatment planning. Phantom measurements using these protocols were performed to determine geometric distortion and to assess reconstruction accuracy of the applicator compared with the ground truth computed tomography image. A treatment plan was created within the treatment planning system that was then delivered to a phantom. New workflows were developed which were tested with a full dry run with a healthy volunteer including patient transfer, anesthesia considerations, and data transfer. Validation of the workflow was completed on 1 patient who received imaging on both the Unity magnetic resonance imaging (MRI) and on a dedicated 3 Tesla MRI simulator. Imaging analysis results were favorable with MR-linac images with a maximum distortion of 0.96 mm and a 1.36-mm over a 350-mm diameter spherical volume on the T1- and T2-weighted images, respectively, and the maximum effect of the applicator was 0.36 ppm of the main magnetic field. Reconstruction uncertainties of the Venezia applicator's tandem and 2 lunar-ovoids on the MR-linac images were within the 2-mm tolerance of the International Commission on Radiation Units and Measurements Report 89. Treatment planning and delivery was performed on the MR-HDR quality assurance phantom without issue. Dry run and healthy volunteer imaging showed adequate performance of both vital monitoring and HDR equipment. For the patient for which both the Unity MRI and 3 Tesla images were acquired, 95.78% and 95.80% of the high risk clinical target volume received 100% of the dose, respectively. Both plans were considered clinically acceptable. Unity MR-linac images were successfully used in gynecologic HDR brachytherapy treatment planning, and a usable workflow was established.

Deep learning-based dose map prediction for high-dose-rate brachytherapy

Background. Creating a clinically acceptable plan in the time-sensitive clinic workflow of brachytherapy is challenging. Deep learning-based dose prediction techniques have been reported as promising solutions with high efficiency and accuracy. However, current dose prediction studies mainly target EBRT which are inappropriate for brachytherapy, the model designed specifically for brachytherapy has not yet well-established. Purpose. To predict dose distribution in brachytherapy using a novel Squeeze and Excitation Attention Net (SE_AN) model. Method. We hypothesized the tracks of 192Ir inside applicators are essential for brachytherapy dose prediction. To emphasize the applicator contribution, a novel SE module was integrated into a Cascaded UNet to recalibrate informative features and suppress less useful ones. The Cascaded UNet consists of two stacked UNets, with the first designed to predict coarse dose distribution and the second added for fine-tuning 250 cases including all typical clinical applicators were studied, including vaginal, tandem and ovoid, multi-channel, and free needle applicators. The developed SE_AN was subsequently compared to the classic UNet and classic Cascaded UNet (without SE module) models. The model performance was evaluated by comparing the predicted dose against the clinically approved plans using mean absolute error (MAE) of DVH metrics, including D 2cc and D 90%. Results. The MAEs of DVH metrics demonstrated that SE_AN accurately predicted the dose with 0.37 ± 0.25 difference for HRCTV D 90%, 0.23 ± 0.14 difference for bladder D 2cc, and 0.28 ± 0.20 difference for rectum D 2cc. In comparison studies, UNet achieved 0.34 ± 0.24 for HRCTV, 0.25 ± 0.20 for bladder, 0.25 ± 0.21 for rectum, and Cascaded UNet achieved 0.42 ± 0.31 for HRCTV, 0.24 ± 0.19 for bladder, 0.23 ± 0.19 for rectum. Conclusion. We successfully developed a method specifically for 3D brachytherapy dose prediction. Our model demonstrated comparable performance to clinical plans generated by experienced dosimetrists. The developed technique is expected to improve the standardization and quality control of brachytherapy treatment planning.

AAPMWGDCAB Report 372:A joint AAPM, ESTRO, ABG, and ABS report oncommissioning 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.

Image-guided permanent I-125 seed implantation for refractory head-and-neck carcinoma in China: A comprehensive review of contemporary technical and clinical aspects

Permanent I-125 seed implantation is one of the most commonly used brachytherapy (BT) forms, potentially applicable to almost any solid tumor as a standalone anti-tumor therapy or in combination with external beam radiotherapy (EBRT). The main advantage of I-125 seed implantation BT is its ability to deliver a high radiation dose within target volumes while maintaining a sharp dose drop-off profile, thereby protecting adjacent normal tissue. The clinical use of I-125 seed implantation in China has significantly increased in the past decades due to the application of an image-guided BT treatment planning system with reverse optimization capabilities and 3D printing individual template (3D-PIT) assistance. Computed tomography-guided I-125 seed implantation became a widely common modality of BT and has been used in many clinical settings for a variety of refractory cancer in China since 2002. The application has been expanded significantly not only for prostate cancer as monotherapy but also in combination with EBRT for the salvage treatment for refractory/recurrent head-and-neck carcinoma (HNC). With the assistance of 3D-PIT, since 2015, the quality control of I-125 seed implantation has been significantly adapted with high precision and real-time dose optimization. This review aims to summarize the developments and status of 3D-PIT-based I-125 seed implantation BT for the treatment of refractory HNC and standardized workflow in China.

Dosimetric and workflow impact of synthetic-MRI use in prostate high-dose-rate brachytherapy

Target and organ delineation during prostate high-dose-rate (HDR) brachytherapy treatment planning can be improved by acquiring both a postimplant CT and MRI. However, this leads to a longer treatment delivery workflow and may introduce uncertainties due to anatomical motion between scans. We investigated the dosimetric and workflow impact of MRI synthesized from CT for prostate HDR brachytherapy. Seventy-eight CT and T2-weighted MRI datasets from patients treated with prostate HDR brachytherapy at our institution were retrospectively collected to train and validate our deep-learning-based image-synthesis method. Synthetic MRI was assessed against real MRI using the dice similarity coefficient (DSC) between prostate contours drawn using both image sets. The DSC between the same observer's synthetic and real MRI prostate contours was compared with the DSC between two different observers' real MRI prostate contours. New treatment plans were generated targeting the synthetic MRI-defined prostate and compared with the clinically delivered plans using target coverage and dose to critical organs. Variability between the same observer's prostate contours from synthetic and real MRI was not significantly different from the variability between different observer's prostate contours on real MRI. Synthetic MRI-planned target coverage was not significantly different from that of the clinically delivered plans. There were no increases above organ institutional dose constraints in the synthetic MRI plans. We developed and validated a method for synthesizing MRI from CT for prostate HDR brachytherapy treatment planning. Synthetic MRI use may lead to a workflow advantage and removal of CT-to-MRI registration uncertainty without loss of information needed for target delineation and treatment planning.

Being certain about uncertainties: a robust evaluation method for high-dose-rate prostate brachytherapy treatment plans including the combination of uncertainties

In high-dose-rate (HDR) prostate brachytherapy the combined effect of uncertainties cause a range of possible dose distributions deviating from the nominal plan, and which are not considered during treatment plan evaluation. This could lead to dosimetric misses for critical structures and overdosing of organs at risk. A robust evaluation method to assess the combination of uncertainties during plan evaluation is presented and demonstrated on one HDR prostate ultrasound treatment plan retrospectively. A range of uncertainty scenarios are simulated by changing six parameters in the nominal plan and calculating the corresponding dose distribution. Two methods are employed to change the parameters, a probabilistic approach using random number sampling to evaluate the likelihood of variation in dose distributions, and a combination of the most extreme possible values to access the worst-case dosimetric outcomes. One thousand probabilistic scenarios were run on the single treatment plan with 43.2% of scenarios passing seven of the eight clinical objectives. The prostate D90 had a standard deviation of 4.4%, with the worst case decreasing the dose by up to 27.2%. The urethra D10 was up to 29.3% higher than planned in the worst case. All DVH metrics in the probabilistic scenarios were found to be within acceptable clinical constraints for the plan under statistical tests for significance. The clinical significance of the results from the robust evaluation method presented on any individual treatment plan needs to be compared in the context of a historical data set that contains patient outcomes with robustness analysis data to ascertain a baseline acceptance.