Room: Track 2
Purpose: To assess the clinical utility of an accessible 3D ultrasound (US) system for guiding placement of gynecologic brachytherapy applicators, providing the potential for intraoperative refinement and assessment of implants and establishing the possibility for US-planned first fraction delivery.
Methods: We have developed a mechanical 3D US system capable of 360° transvaginal (TVUS) and transrectal (TRUS) imaging (depending on patient geometry) in <20 s by rotating a 2D US probe. These approaches have been assessed in two interstitial brachytherapy trials, including 12 patients (126 needles) combined, where positions were evaluated against standard post-insertion CT images. To improve the clinical workflow, live 2D and post-insertion 3D automatic needle segmentation using deep-learning and Hough transform-based approaches, respectively, has been implemented for TVUS and evaluated against manual segmentations. A Patterson-Parker-style approach was employed for preliminary comparison of CT-based and TVUS-based interstitial isodose volumes. A proof-of-concept trial is ongoing to assess 3D TRUS for intracavitary applicators with one ring-and-tandem and three tandem-and-ovoids patients imaged.
Results: In interstitial patients, nearby organs-at-risk, including bladder and rectum, were clearly visualized. Needles demonstrated mean position and angular differences of <3.9 mm and <3.1°, respectively, for both imaging modes, despite differences in patient positioning between US and CT. The 2D and 3D automatic segmentations demonstrated mean position and angular differences of 0.6 ± 1.2 mm and 0.5 ± 0.5° (n=18) and 1.0 ± 0.4 mm and 1.1 ± 0.9° (n=68), respectively. The mean dose cylinder radius difference (7 patients) was 0.8 ± 0.9 mm. Tandem-and-ovoids applicators were better visualized than ring-and-tandem, with less shadowing, and allowed clear visualization of the vagina, cervix, tumour, bladder, and rectal wall.
Conclusion: Intraoperative guidance using the proposed 3D US system has the potential to be a versatile and accessible approach to interstitial and intracavitary applicator verification and assessment, even in resource-constrained settings.
Funding Support, Disclosures, and Conflict of Interest: The authors gratefully acknowledge the funding support from the Ontario Institute for Cancer Research (OICR), the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Institutes of Health Research (CIHR).