Dosimetry of a sonolucent material for an ultrasound-compatible gynecologic high-dose-rate brachytherapy cylinder using Monte Carlo simulation and radiochromic film

Clinical implementation of 3D transvaginal ultrasound for intraoperative guidance of needle implant in template interstitial gynecologic high-dose-rate brachytherapy

PURPOSE

To demonstrate novel clinical implementation of a 3D transvaginal ultrasound (3DTVUS) system for intraoperative needle insertion guidance in perineal template interstitial gynecologic high-dose-rate brachytherapy and assess its impact on implant quality.

METHODS AND MATERIALS

Interstitial implants began with preimplant 3DTVUS to visualize the tumor and anatomy, with intermittent 3DTVUS to assess the implant and guide needle adjustment. Analysis includes visualization of the implant relative to anatomy, identification of cases where 3DTVUS is beneficial, dosimetry, and a survey distributed to 3DTVUS clinicians.

RESULTS

Seven patients treated between November 2021 and October 2022 were included in this study. Twenty needles were inserted under 3DTVUS guidance. The tumor and vaginal wall were well-differentiated in four and all seven patients, respectively. Patients with tumours below the superior aspect of the vagina are suited for 3DTVUS. Four radiation oncologists responded to the survey. There was general agreement that 3DTVUS improves implant and anatomy visualization and is preferred over standard 2D ultrasound guidance techniques.

CONCLUSIONS

Based on qualitative feedback from primary users and a small preliminary patient cohort, 3DTVUS imaging improves tumor and vaginal wall visualization during gynecologic perineal template interstitial needle implant and is a powerful tool for implant assessment in an intraoperative setting.

3D printing in brachytherapy: A systematic review of gynecological applications

PURPOSE

To provide a systematic review of the applications of 3D printing in gynecological brachytherapy.

METHODS

Peer-reviewed articles relating to additive manufacturing (3D printing) from the 34 million plus biomedical citations in National Center for Biotechnology Information (NCBI/PubMed), and 53 million records in Web of Science (Clarivate) were queried for 3D printing applications. The results were narrowed sequentially to, (1) all literature in 3D printing with final publications prior to July 2022 (in English, and excluding books, proceedings, and reviews), and then to applications in, (2) radiotherapy, (3) brachytherapy, (4) gynecological brachytherapy. Brachytherapy applications were reviewed and grouped by disease site, with gynecological applications additionally grouped by study type, methodology, delivery modality, and device type.

RESULTS

From 47,541 3D printing citations, 96 publications met the inclusion criteria for brachytherapy, with gynecological clinical applications compromising the highest percentage (32%), followed by skin and surface (19%), and head and neck (9%). The distribution of delivery modalities was 58% for HDR (Ir-192), 35% for LDR (I-125), and 7% for other modalities. In gynecological brachytherapy, studies included design of patient specific applicators and templates, novel applicator designs, applicator additions, quality assurance and dosimetry devices, anthropomorphic gynecological applicators, and in-human clinical trials. Plots of year-to-year growth demonstrate a rapid nonlinear trend since 2014 due to the improving accessibility of low-cost 3D printers. Based on these publications, considerations for clinical use are provided.

CONCLUSIONS

3D printing has emerged as an important clinical technology enabling customized applicator and template designs, representing a major advancement in the methodology for implantation and delivery in gynecological brachytherapy.

A Dosimetric evaluation of a high dose rate cobalt-60 brachytherapy source using shielded, single and multi-channel cylinder applicators for gynecological cancers

Vaginal brachytherapy is a standard method for preventing the recurrences of malignancies in the treatment of gynecological cancers. Cylindrical applicators are usually employed in high dose rate cobalt-60 source brachytherapy after abdominal hysterectomy or bilateral salpingo-oophorectomy treatment. The aim of this study is to conduct an assessment of dosimetric properties of single channel, multichannel, and shielded cylinder applicators. This study utilizes a pelvis phantom with three different volumes of bladder and rectum to perform dose measurement around the cylindrical applicators. GAFCHROMIC EBT3 model film was used to measure dose distributions in water phantom around the bladder, rectum, applicator, and CTV. In order to properly compare the performance of the shielded applicator with multichannel and single channel applicators, we consider the both cases of a one-sided CTV and two CTVs placed on both sides of the vagina. Dose-volume histograms analysis shows no statistically significant difference in tumoral region for the two types of CTV between cylindrical applicators. The V_120%, V_100% and D_95% values of target volume were 47.36%. 91.46%, and 3.99Gy for multi-channel cylinder applicator, 60.2%, 95.02%, and 3.99Gy for single channel cylinder applicator, respectively. Statistical analysis reports D_0.1cc, D_1cc, and D_2cc for the multichannel applicator demonstrates a significant dose reduction in bladder compared with single channel. The V_120%, V_100%, and D_95% values of target volume were 55.50%. 97.90%, and 3.91Gy for multi-channel cylinder applicator with four active channels (MCC-4), 41.56%, 92.10%. and 4.13Gy for shielded cylinder applicator, respectively. Statistical analysis reports D_0.1cc, D_1cc and D_2cc for the MCC-4 demonstrates a noticeable dose reduction in bladder and rectum compared with Shielded channel. The results indicate that employing multichannel applicator in vaginal high dose rate cobalt-60 source brachytherapy can reduce the received dose to organs at risk without any significant loss of received dose in CTV, which is contributed to its asymmetric or symmetric dose distribution that depend on which channels are activated.

Technical Note: Commissioning of an ultrasound-compatible surrogate vaginal cylinder for transvaginal ultrasound-based gynecologic high-dose-rate brachytherapy

PURPOSE

To provide a comprehensive set of commissioning tests for clinical implementation of three-dimensional transvaginal ultrasound (3D TVUS) as a replacement of computed tomography (CT) for applicator reconstruction in gynecologic intracavitary high-dose-rate brachytherapy with a multi-channel vaginal cylinder.

METHODS

We introduce an ultrasound-compatible "surrogate" vaginal cylinder (SVC) for reconstruction of Elekta's CT-MR Multi Channel Applicator (MCVC) in 3D TVUS. The MCVC is digitized over the SVC in 3DUS using digital library model overlay. Consulting guidelines from various sources (CPQR, GEC-ESTRO, AAPM), we identify and describe three tests specific to commissioning the SVC: 1) verification of SVC outer dimensions, 2) source position accuracy of MCVC digitization over the SVC in 3D TVUS, and 3) MRI/US registration error.

RESULTS

The SVC outer dimensions (diameter and A-D marker locations) were well matched to the MCVC, however a 0.6 mm discrepancy in length between cylinder tips was observed. Source position accuracy was within 1 mm (tolerance recommended by CPQR) when reconstructing the MCVC in 3D TVUS. Dice similarity coefficients and target registration error for MRI/3D TVUS registration was similar to MRI/CT registration, which is the clinical standard.

CONCLUSIONS

These commissioning tests are performed using institutional equipment but provide the framework for any practitioners to repeat in their own setup, to demonstrate safe adoption of the 3D TVUS system for patient treatments. We demonstrate that MRI/US-based workflow achieves similar source position accuracy and image registration error as standard MRI/CT, which is consistent with standard tolerances. This is a critical step towards replacement of CT with US in gynecologic high-dose-rate brachytherapy treatments with the MCVC. This article is protected by copyright. All rights reserved.