TPS2105 Background: Glioblastoma remains a lethal primary brain tumor with limited therapeutic progress and a persistent unmet clinical need. Standard management requires maximal safe resection followed by external beam radiation therapy (EBRT) with concurrent temozolomide (TMZ); however, the required 4–6-week postoperative healing interval before initiating EBRT creates a vulnerable window for rapid early progression (REP), defined as radiographic tumor progression occurring between surgery and the start of chemoradiation. REP is detected in more than half of patients and is associated with inferior survival. Tile-based radiation therapy (TBRT) with cesium-131 brachytherapy sources (GammaTile, GT Medical Technologies, Tempe, AZ, USA), offers a strategy to eliminate this treatment gap by immediately initialing localized radiation at the time of resection. A feasibility and safety study (NCT05342883) evaluating TBRT implantation following EBRT has been fully accrued and supports randomized evaluation. The BRIDGES study (NCT07195591) builds on this foundation. Methods: NCT07195591 is a prospective, randomized, open-label, multicenter, phase 3 trial to evaluate whether immediate postoperative TBRT followed by abbreviated EBRT with concurrent and adjuvant TMZ improves outcomes compared with standard postoperative EBRT with concurrent and adjuvant TMZ. Eligible adults must have newly diagnosed, radiographic suspicion of glioblastoma, can undergo maximal safe resection, possess a Karnofsky Performance Status score ≥70, and be candidates for standard chemoradiation. Key exclusion criteria include multifocal or disseminated disease, prior cranial radiation or chemotherapy, inability to receive TMZ, and medical comorbidities that would interfere with protocol treatment or follow-up. Patients are randomized 2:1 to receive either TBRT implantation followed by a shortened EBRT course with concurrent and adjuvant TMZ or standard postoperative EBRT with concurrent and adjuvant TMZ. Randomization is stratified by age, sex, prior sub-maximal safe resection, and size of pre-operative tumor. A stratified log-rank test using Kaplan–Meier methods will be done using the stratification factors will be implemented for the primary endpoint. Additional time-to-event endpoints will be analyzed using Kaplan–Meier methods and Cox proportional hazards models, and the analyses will follow the intent-to-treat principle. The trial has two pre-planned interim analyses. A Data and Safety Monitoring Board will oversee the trial and conduct periodic safety reviews. Four of the 766 planned patients have enrolled. Clinical trial information: NCT07195591 .

Background:Cesium-131 collagen tile has gained traction as an intraoperative brachytherapy platform for recurrent intracranial tumors, but outcome data in newly diagnosed brain metastases (nBM) remain sparse, with fewer than ten cases reported. This study evaluates the safety and efficacy of cesium-131 collagen tiles in nBM patients. Methods:Clinical information was collected for consecutive nBM patients treated at three neurosurgical centers. Local control and overall survival (OS) were calculated. Results:The cohort comprised 36 patients (14 men, 22 women; mean age, 62.1 ± 8.9 years) with 39 nBM. Histologies included lung (n = 19), melanoma (n = 8), breast (n = 4), gastrointestinal (n = 3), and genitourinary (n = 5) metastases. The mean pre-operative tumor diameter was 3.29 ± 1.35 cm. Gross total resection was achieved in all but one case. Mean Karnofsky Performance Score (KPS) before resection/tile implant was 81 ± 11.1. The average hospital stay was 2.2 ± 1.6 days. Thirty-day and 90-day readmission rates were 25.0% and 19.4%, respectively; there were no unplanned returns to the operating room. With a median follow-up of 328 days, one-year actuarial local control was 100%, with one recurrence at two years. Median overall survival (OS) was 182 days. Radiation necrosis was observed in one patient (2.6%). KPS improved or remained stable in 28 patients (77.8%) and declined in 8 (22.2%). A decline in KPS at one month post-procedure was associated with shorter OS (65 vs. 211 days; P = .02). Conclusion:This multi-institutional study provides the first dedicated evaluation of cesium-131 collagen tiles for the treatment of nBM, demonstrating excellent safety and local control.

Local control remains a major challenge in the surgical management of recurrent glioblastomas. Brachytherapy, such as Gammatile, offers a promising solution by delivering targeted radiation to the surgical bed. Here, we report the outcome of 60 consecutive recurrent glioblastoma patients who underwent resection/GT-implant. Clinical information was collected for consecutive, recurrent glioblastoma (isocitrate dehydrogenase wild-type) patients treated at the University of Minnesota, Honor Health, Robert Wood Johnson, Emory, Allegheny Health, East Carolina University, and Inova. Median progression-free and overall survival (mPFS and mOS) were calculated from the time of GT implant and stratified by methyl-guanine-methyl transferase (MGMT) status. The study cohort comprised 47 male and 13 female subjects, with 1-3 previous glioblastoma recurrences. Karnofsky Performance Score (KPS) decreased post-resection/GT implant in 24 patients (41.2%); all experienced functional recovery, but to variable extents. Surgical/GT morbidities (6%) included hemorrhage, wound infection, and radiation necrosis (each at 1/60 or 2%). The median hospital stay was 2 days (range: 1- 21 days). 16.7% of the cohort required 30-day readmission, comparable to the expected readmission rate for craniotomy alone. There was no instance of rapid early recurrence, defined as tumor regrowth in the first MRI following surgical resection. Actuarial local control at one year was 92% and 80% for MGMT-methylated and -unmethylated patients, respectively (p=0.17). MGMT-methylated patients showed improved OS (mOS=14.7 mo) compared to unmethylated patients (mOS=7.9 mo, p=0.01). These results compare favorably to historical survival for these patient cohorts. Patients who showed a KPS decline after resection/GT-implant showed reduced OS relative to those with stable/improved KPS (mOS of 388 and 218 days, respectively, p=0.03). The number of tumor recurrences or prior bevacizumab did not prognosticate survival. This multi-institutional experience supports the safety and efficacy of GT brachytherapy and provides a basis for selecting patients who would most benefit from this treatment.

Background and purpose High-dose-rate (HDR) brachytherapy relies on accurate and metrologically traceable source strength determination. Recent anecdotal reports and preliminary studies have suggested a possible temporal drift in the reference air kerma rate (RAKR) measured by clinical users compared to manufacturer certificates for 192Ir sources. This study investigates the existence and magnitude of such drift across a large, multicenter European dataset and explores potential underlying causes. Materials and methods A total of over 1700 RAKR measurements for HDR and PDR brachytherapy sources, collected over two decades from 29 centers in 10 European countries, were analyzed. The ratio of hospital-measured RAKR to manufacturer-certified RAKR was assessed using linear regression and t-tests to evaluate drift. Data were corrected for center-dependent systematics and segmented around key dates corresponding to changes in primary standards. Supplementary analyses included leave-one-out testing and time-segmented trend assessment. Results A statistically significant drift (+0.15 %/year) was detected for all 192Ir source types after 2018, correlating temporally with updates in the German Physikalisch-Technische Bundesanstalt (PTB) primary standards laboratory. Removing PTB corrections from manufacturer values nearly eliminated the observed drift. No such trend was observed for 60Co sources. Conclusion The findings reveal a drift in hospital-to-manufacturer Ir-192 RAKR ratios that is temporally correlated with changes in metrology standards, not uniformly implemented across calibration chains. The true cause is however still unknown. The study aimed to investigate that greater transparency and harmonization among all stakeholders are essential to ensure dosimetric accuracy in HDR brachytherapy.

There are compelling rationales for considering brachytherapy, such as Gammatile (GT), at the time of brain metastasis (BM) resection, including superior radiation dosimetry, timely radiation delivery, and minimizing the burden of repeated hospital visits. While such practice is documented in recurrent BM, there is limited information on its use for newly diagnosed BM (nBM). Here, we report the outcome of 36 nBM patients who underwent resection/GT implant. Clinical information was collected for consecutive n BM patients treated at the University of Minnesota, Westchester Medical Center, and Brown University. Actuarial local control and overall survival (mOS) were calculated from the time of GT implant. The cohort comprised 17 men and 19 women (mean age: 61.9 ± 8.66 years). The histology included: 19 lung, 8 melanoma, 5 breast, 3 gastrointestinal, and 1 valvular cancer. The mean diameter of the resected BM was 3.28 ± 1.35 cm. Gross total resection was achieved in all but one subject. The number of GT used ranged 4-12 (median of 6). The average Karnofsky Performance Score (KPS) before resection/GT implant was 81 ± 11.1; There were no peri-operative complications, with the average hospital stay of 2.2 ± 1.6 days. There were eight 30-day readmissions (22%). KPS improved/remained stable for 29 patients and worsened in 7. With the median follow-up of 328 days, the actuarial local control at one year was 91.7%. The median overall survival (OS) of the cohort was 182 days. Pre-operative KPS did not associate with OS (77 vs. 199 days, p=0.232). However, patients whose KPS declined after the resection showed shorter OS (65 vs. 211 days, p=0.02). This series is the largest to date documenting GT for newly diagnosed BM, with a highly favorable safety and efficacy. KPS decline post-resection is associated with poor survival, emphasizing the importance of a “safe” resection.

OBJECTIVE:To develop and validate a practical method for accurate dose calculations of low-dose-rate brachytherapy treatment of eye tumors. METHODS:Dose calculations of 16 mm Collaborative Ocular Melanoma Study (COMS) and 20 mm notched eye plaques with 125I seeds were performed using the egs_brachy package of the EGSnrc Monte Carlo (MC). Several eye phantoms were modeled, including: (1) uniform phantoms made of only tumor (T), water, or vitreous body (VB) medium; (2) scaled water (SW) and scaled VB (SVB) distributions were derived by scaling the precomputed distributions for all-water and all-vitreous geometries by the relative energy absorption coefficient or each ocular structure to that of water or the vitreous body, respectively; (3) fully defined eye phantom with all structural materials defined; and 4) TG-43 calculations. Two contrasting tumor locations were modeled in this work. For investigation of dose distribution with standard plaques, the tumor was symmetrically located on the medial side of the eye. For the notched plaque, dose distributions were investigated with the tumor located posteriorly (abutting the optic nerve). RESULTS:Compared to the fully-defined phantom calculations, all-water phantom calculations underestimated the tumor dose by 15-20%, while overestimating the lens and sclera dose. The optic nerve dose was predicted correctly. VB phantoms underestimated the tumor coverage by ∼3.5%, while T phantoms accurately predicted the target coverage. Both VB and T phantoms overestimated the organ-at-risk (OAR) doses more than all-water phantom. SW and SVB phantoms accurately predict both tumor and OAR doses within 4% of the complete phantom values for small volume metrics. Dose differences decreased to < 2% to volumes > 20%. CONCLUSION:The dose scaling methodology provides a practical approach to account for ocular heterogeneity effects. This leads to accurate dosimetry, without computational penalties associated with patient-specific MC calculations. The methodology is found to be robust and applicable to both standard COMS and notched eye plaques of different sizes.

This report defines practical guidelines for (a) commissioning a TG-43-based treatment planning system for brachytherapy, and (b) establishing a continuous quality assurance program for the TPS. The main functionalities of the TPS are described, including image import and geometry, source specification, dose calculation, applicator specification and treatment plan data output, and recommended tests are given. For all tests, the frequency and tolerance are summarized in tables. For the different imaging modalities detailed descriptions of the necessary phantoms are provided in the supplementary data. These guidelines aim to help physicists to setup a comprehensive quality management program for BT TPSs.

The management of recurrent meningioma is challenging. Multimodality treatments, including combining resection with implantable collagen-tile cesium-131 brachytherapy (STaRT) (GammaTile®, GT Medical Technologies, Tempe, AZ, USA), may be a good therapeutic option. To assess the efficacy of resection and STaRT for management of aggressive recurrent meningioma on a prospective, multi-center observational study. The first 44 consecutive patients with recurrent meningioma enrolled on the observational registry (NCT04427384) were assessed at 21 centers for patient demographics, tumor characteristics, local control (LC), and adverse events (AEs). These data were collected from 1/28/2021-5/16/2025. Patients with recurrent meningioma (six World Health Organization Grade 1, twenty-one Grade 2, and seventeen Grade 3) underwent resection and STaRT. Expressed a medians, age was 61 years (24-83), follow-up was 11.2 months (0.2-36.1), and maximum preoperative tumor diameter was 4.3 cm (1.2-9.8), 90.5% had prior radiation, with a median interval of 38.4 months (3.4-126.3). By Grade, LC at 6, 12, and 15 months were 83.3%, 83.3%, and 66.7% for Grade 1; 100.0%, 68.6%, and 68.6% for Grade 2; and 92.9%, 76.0%, and 63.3% for Grade 3. For all Grades combined, LC at 6, 12, and 15 months were 94.4%, 78.3%, and 67.0%. Progression-free survival (PFS) by grade at 6, 12, and 15 months were 83.3%, 83.3%, 66.7% for Grade 1; 84.6%, 52.7%, and 52.7% for Grade 2; and 60.0%, 20.0%, and 13.3% for Grade 3. For all Grades combined, PFS at 6, 12, and 15 months were 74.6%, 45.5%, and 37.1%. Median overall survival has not been reached. Seven patients (15.9%) had eight Grade ≥3 AEs (3 infection/dehiscence, 2 each hematoma and edema/necrosis [1 radiation-related], and 1 seizure). This report from 21 centers demonstrates that resection plus STaRT for aggressive, recurrent meningiomas resulted in encouraging LC and low AE rate.

Purpose Migration of tumor cells away from the focal source of radiation may facilitate resistance to brachytherapy. While the mechanisms mediating chemotaxis from noxious stimuli are well-established, it remains unclear whether tumor cells harbor intrinsic molecular circuits that mediate migration away from focal radiation sources. Here, we examined this question using real-time imaging of glioblastoma cells. Materials and Methods Green fluorescent protein-labeled U251MG (GFP-U251MG) cells were plated on 2.5-dimensional collagen gel at fixed distances relative to cesium-131 brachytherapy seeds (Fig. 1a). The proliferation and migration of these cells were monitored using time-lapse microscopy at a single-cell level as a function of the cumulative radiation dose of brachytherapy. Results Cell death was observed for GFP-U251MG cells exposed to >30 Gy (Fig. 1b). For cells receiving sub-lethal dose radiation, cell migration speed (∼1 µm/min in the absence of radiation) decreased exponentially with increasing radiation exposure (reduced to ∼0.3 µm/min at the cumulative dose of 20 Gy) (Fig. 1c). About 75% of viable cells migrated away from the Cs-131 seeds with the mean forward migration indices of 0.1 (p = 0.0017) (Fig. 1d) relative to the expected migration pattern predicted based on non-directional, random migration. Single-cell tracking showed cells migrated toward the radiation source and were more likely to undergo cell death (Fig. 1e), while those that migrated away from the radiation source were more likely to proliferate (Fig. 1f). Conclusions These findings suggest a previously undescribed cellular behavior that we termed radiotaxis, defined as migration away from a focal source of radiation, which confers radio-resistance to brachytherapy. The conceptual framework of radiotaxis predicts synergy between brachytherapy and tumor migration inhibitors, a hypothesis that awaits validation.

Purpose In Ir-192-based high dose rate (HDR) brachytherapy, the dose delivered at the central axis of single-channel vaginal cylinder (SCVC) is inherently lower than the surrounding areas due to the anisotropic dose distribution of the Ir-192 seed. In principle, this situation could be addressed by introducing custom shielding into the dome of SCVC to shape the dose distribution near the central axis. Aided by advanced dose calculation methods, including both Monte Carlo (MC) simulations and Model-Based Dose Calculation Algorithms (MBDCAs), the shape and density of the shielding materials could provide additional degrees of freedom for inverse dose optimization. In this work, we investigate the potential benefits of this approach by investigating the efficacy of an SCVC with custom shielding (SCVC+S) design to flatten the distal dose profile. Materials and Methods A standard SCVC with 140 mm cylinder height (h) and 30 mm outer diameter (OD) with an air channel of 1.6 mm along the central axis for the source transit was used in the initial investigation. The cylinder is capped by a half-spherical dome with a matching diameter (d) of 30 mm. While the existing SCVC is composed entirely of water-equivalent material, the SCVC+S design includes a cavity within the dome which will be injected with stainless steel (mass density of 8.0 g/cc, 6.49 electron density, 13415 HU) shielding material. Three distinct SCVC+S dome designs were explored: A) dome composed of entirely stainless steel except an air channel of d=5 mm along the central axis; B) dome containing one disk “washer” (OD=27 mm, inner diameter (ID)=20 mm, h=1 mm); C) dome containing one disk “washer” (OD=13 mm, ID=3 mm, h=2.5 mm) stacked on a short cylinder (d=13 mm, h=2.5 mm). The SCVC/SCVC+S geometries were independently modeled, with the GammaMed Plus 232 HDR 192Ir (dosimetrically identical to Bravos 232A HDR192) radioactive source model for 1) AcurosBV v1.8.0.867816 (Varian Medical Systems, Palo Alto, CA) MBDCA, with dose reported to medium for a 1 × 1 × 1 mm3 grid; and 2) Geant4 MC with TOPAS v3.8 toolkit, with tracklength estimator (TLE) dose for 1 × 1 × 1 mm3 grid, with n=1 × 108 histories. Results After modeling the 4 (one SCVC and three SCVC+S) applicator designs in EclipseBV and TOPAS, the dose grids were obtained. PORTEC A3 (3.5 mm lateral, 5 mm superior) reference point and lateral dose profiles up to lateral radius (r) of 15 mm were extracted from a plane 5 mm superior to the SCVC tip (normalized to 100% dose at the central axis). The traditional SCVC has region of lowest dose at central axis, with large shoulders, 109% dose at A3, 116% dose at r=10 mm. Design A of SCVC+S has its highest relative dose at central axis, with no shoulders, 92% dose at A3, 61% dose at r=10 mm. Design B of SCVC+S has a wide flat region with shoulders, 100% dose at A3, 104% dose at r=10 mm. Design C of SCVC+S has a high central region with large shoulders, 94% dose at A3, 82% dose at r=10 mm. Conclusions Traditional SCVC inevitably create regions near the central axis with lower relative dose than the surrounding region. Our initial MBDCA and MC simulations show promising results which demonstrate that a simple stainless steel “washer” embedded in the tip can provide a viable filter to produce a uniform dose profile at the 5 mm depth plane. In addition, a redesign of the shielding could turn the central axis into a region of highest dose, reversing the classic SCVC dose profile. Our ongoing work is investigating computational methods to optimize stainless steel disk shapes (namely h, ID, OD) to flatten the profile at arbitrary depths and different cylinder diameters. We are also working with our institution's 3D Collaborative for Medical Innovation (3DC) for rapid physical prototyping of our SCVC+S design.

Purpose/Objective(s) Since the publication of TG-192 report in 2014, improvements in robotic brachytherapy technology have been realized and many new robotic systems were developed. Some of these devices are also being used clinically. In response to these progresses, the AAPM Brachytherapy Subcommittee and GEC-ESTRO BRAPHYQS Subcommittee assembled a joint task group (TG-342) for updating TG-192 report and providing comprehensive guidelines for implementation of robotic devices in clinic. Materials/Methods TG-342 report includes robotic systems developed in the past 10 years (after publication of TG-192). A 12-member international committee of TG-342 has gathered information and prepared a report. There is minimal overlap with TG-192 as far the robotic systems are concerned. However, there are some overlaps in methodology of clinical applications and recommendations. Results Most of the new systems differ from each other with respect to available features, functionalities, and levels of automation. They are either US guided or CT guided, only 3 systems are MRI guided. About 50% of the systems are needle guides with manual needle insertion, rest of the systems accommodate autonomous needle insertion. Reported accuracy of needle or catheter placement ranges from 0.9 to 2.9 mm. Several new robotic systems have successfully been translated to clinic and the reported clinical outcomes are encouraging. In TG-342, a total of nineteen new robotic systems are described and their specifications, status, and applications are illustrated. Unlike the robotics systems in TG-192 focused on prostate seed implantation (PSI), the new robotic systems in TG-342 are developed to perform HDR brachytherapy as well as seed implantation to lung, liver, breast, and other anatomical sites in addition to PSI. Many of these systems are designed for hybrid applications, i.e., extending the application to biopsy, RFA, and IORT, beyond LDR and HDR brachy. In addition, the recommendation section has been expanded. Conclusion International initiatives to develop brachytherapy robots have been realized; a vast majority of the new 19 systems are reported from Asia (8) and Europe (8). Some of these robotic systems have been used clinically. Increased involvement of industry as well as industry:university collaboration are remarkable. Currently available brachytherapy robotic systems greatly vary in design, characteristics, features, and imaging modalities. Therefore, the TG-342 report provides general, rather than very strict recommendations and encourages all researchers to develop and document their own calibration procedures specific for their robotic system. An increasing number of robotic systems transitioning into clinical practice is anticipated.

BackgroundLarge reported variability in the material composition and geometrical components of the Xoft electronic high-dose-rate brachytherapy Causes inter-source discrepancy in the source output. This variability is due to the manual manufacturing and assembly of the sources.PurposeThis study aimed to develop a dosimetry software tool called E-Brachy to characterize the Xoft source and quantify the discrepancies in its photon spectrum and dosimetric properties.MethodsE-Brachy is based on the Geant4 Monte Carlo toolkit and consists of two parts. In part one, the geometry and material composition for the source received in the computer-aided design format from the vendor were converted to the geometry description markup language format using the GUIMesh Python tool and integrated into the E-Brachy software. There was a large variation in material composition and thickness for some of the tube components. The simulation started from electrons and resulted in x-ray generations in the anode region. Multithreading, a track length estimation, and the uniform bremsstrahlung splitting variance reduction techniques were used to decrease the simulation time and increase the x-ray production. The photon energy, position, and momentum were saved into a phase space file as the photon exited the source, but before interacting with the external environment. The obtained x-ray energy spectrum was compared with measurements from the National Institute of Standards and Technology (NIST). In part two, by sampling from the generated photons, the dose rates and dosimetric parameters according to the TG-43 protocol were calculated for model S7500 and compared to the ones previously calculated for model S700 source, which were deemed identical by the manufacturer.ResultsThe material composition that resulted in the most similar spectrum as the measured NIST spectrum with Pearson's correlation coefficient of 0.99 and a calculated Euclidean difference of 0.061 +/- 0.001$0.061\,\pm \,0.001$ keV was chosen for further dosimetric analysis of the model S7500 source. Characteristic peaks showed the presence of tungsten, yttrium, and silver in the source components. Differences in dose rates between the two source models surpassed 20% for polar angles theta >= 150 degrees$\theta \,\ge \,150<^>\circ$, reaching a peak at r=3$r\,=\,3$ cm and theta=175 degrees$\theta \,=\,175<^>\circ$. The differences in the radial dose function values were within 5%. The relative difference in percentage between the anisotropy function values of the two models was closer to 0 for smaller theta$\theta$ values, but at higher polar angles, they increased to 300%.ConclusionsA software package called E-Brachy was successfully developed for the characterization and dosimetry of Xoft electronic brachytherapy sources. E-Brachy can be combined with spectral measurements to investigate the inter- and intra-source variability. The software package was tested by comparing the simulated spectra from the S7500 Xoft source model with NIST measurements and its TG-43 parameters with the S700 model. The TG-43 parameters between the two sources significantly exceed the recommendations of TG-56.

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.

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.

Purpose This presentation shares highlights of the International Atomic Energy Agency (IAEA) Technical Report Series 492 Code of Practice on brachytherapy (BT) dosimetry. Methods This IAEA Code of Practice is addressed to both secondary standards dosimetry laboratories (SSDLs) and hospitals, not addressed to primary standards dosimetry laboratories (PSDLs), and is based on the use of well-type re-entrant ionization chambers. It applies to all BT sources with intensities measurable by such detectors. The dosimetry formalism, common procedures for reference dosimetry and for calibration, reference-class instrument assessment, and commissioning of well-type chamber system are described. This Code of Practice is aimed to enable common procedures to perform dosimetry of radioactive sources used in BT, excluding beta-emitting eye plaques/applicators as well as stranded seeds and mesh-type sources. Targeted radionuclide therapy and miniature electronic brachytherapy (eBT) devices were also excluded. It provides a description of the most accurate and sensitive calibration systems available at PSDLs and recommends suitable detectors and procedures for source strength measurements at SSDLs and hospitals. Results This Code of Practice consists of ten sections and six appendices. Following the introduction in Section 1 that frames the background and scope, Section 2 provides a description of the radioactive sources currently available for BT. The dosimetric quantities reference air kerma rate, air kerma strength and absorbed dose to water are discussed in Section 3, along with the dose-rate constant and other parameters important to dosimetrically characterize BT sources. Section 4 provides a detailed description of well-type ionization chamber instrumentation and defines the requisites for reference-class instruments. It also includes a description of HDR remote afterloaders. Section 5 contextualizes the dosimetry framework that defines dissemination of primary dosimetry standards down to the hospital level. Section 6 provides an overview of the available primary standards useful for BT calibrations. Their dissemination through the adoption of a well-type chamber dosimetry system is furthermore described. Section 7 defines the dosimetry formalism employed for the determination of the dosimetry quantities used herein. The general procedure to properly perform BT dosimetry with the well-type chamber is given in Section 8, along with a description of methods to check for short and long term stability of the measurement system. Section 9 deals with estimating uncertainties typically involved with source strength measurement of LDR and HDR sources. The way measured reference quantities are useful in the clinical practice for assessing the dose to the patient is outlined in Section 10. The main BT source categories and treatment delivery methods are briefly approached. Appendices are provided to complement the information given in the main body of the publication: Appendix I briefly mentions antiquated quantities and units that are not recommended to be used any more for dosimetry purposes; Appendix II provides insight into the present situation for dosimetry standards based on air kerma and absorbed dose to water; Appendix III provides a brief description of eBT devices and the current status of their dosimetry standards; Appendix IV provides insight into some detector systems different from the well-type ionization chamber that might be used for BT dosimetry; Appendix V describes the formalism found in the AAPM Task Group 43 Report, which is commonly used for dose distribution calculation in interstitial and intracavitary BT; Appendix VI introduces the theory for estimating measurement uncertainties. Conclusions Guidance and recommendations for BT dosimetry in relation to identified good practices are presented for international harmonization.