ESTRO 2025 - Abstract Book

S388

Brachytherapy - Urology

ESTRO 2025

Conclusion: SIMF HDR-BT for localized PrC demonstrates excellent feasibility and favorable short-term outcomes in an LMIC setting, with significant cost savings. This approach offers a practical and effective strategy for improving cancer care equity in resource-limited settings.

Keywords: High dose rate, single-insertion, LMIC

References: 1. Hoskin PJ, Colombo A, Henry A, Niehoff P, Paulsen Hellebust T, Siebert FA, et al. GEC/ESTRO recommendations on high dose rate afterloading brachytherapy for localised prostate cancer: An update. Radiotherapy and Oncology. 2013 Jun;107(3):325–32. 2. Yamada Y, Rogers L, Demanes DJ, Morton G, Prestidge BR, Pouliot J, et al. American Brachytherapy Society consensus guidelines for high-dose-rate prostate brachytherapy. Brachytherapy. 2012 Jan;11(1):20–32. 3. Yap ET, Dumago MP, Jainar CJ, Bojador M, Cabrera SM, Gonzalez GS, et al. Clinical outcomes of single application multi-fractionated CT-guided interstitial high-dose-rate brachytherapy for locally advanced cervical cancer: A multi institution initial experience. jcb. 2023;15(6):399–404.

3203

Proffered Paper Updated results of MR-assisted focal salvage HDR prostate brachytherapy: a prospective study Hans T Chung 1,2 , Gregory Paulin 1 , Andrew Loblaw 1,2 , Chia-Lin Tseng 1,2 , Ananth Ravi 2 , Melanie Davidson 1 , Matt Wronski 1,2 , Moti Paudel 1,2 , Masoom Haider 3 , Andrea Deabreu 1 , Gerard Morton 1,2 1 Radiation Oncology, Sunnybrook Odette Cancer Center, Toronto, Canada. 2 Radiation Oncology, University of Toronto, Toronto, Canada. 3 Medical Imaging, University of Toronto, Toronto, Canada Purpose/Objective: Because multiparametric MRI can generate detailed images of the anatomic extent of cancer within the prostate, its integration in salvage therapies such as brachytherapy has been widely embraced. It has enabled focal therapies and whole-gland therapies with intra-prostatic boost. The objective is to update the efficacy and toxicity results of our prospective, phase 2 study of MR-assisted focal-gland salvage HDR prostate brachytherapy in patients with local recurrent prostate cancer. Material/Methods: Eligible patients included: multiparametric 3T MRI (mpMRI) visible biopsy confirmed local recurrence >30 months after radiotherapy, negative metastatic workup, and IPSS <15. Ultrasound-based HDR brachytherapy with intraoperative contour-based deformable registration between the mpMRI and ultrasound images were done in 44 of 59 patients, and cognitive fusion in the remaining 15 patients. The prescription dose was 27Gy to the MR-defined intraprostatic target volume (TV) divided over two implants separated by 1-2 weeks with dose constraints to the urethra and rectum. Adjuvant androgen deprivation therapy (ADT) was not used. Post-treatment response was evaluated using mpMRI 1-2 years after salvage. Follow-up PSA, IPSS and CTCAE v4.0 toxicities were collected. Results: 59 patients were enrolled in the study. Median follow up from salvage HDR was 54 months (11-132). At initial presentation, there were 19, 37 and 3 low-, intermediate- and high-risk disease. The initial treatment was external beam radiotherapy (XRT) only in 20 (34%) and brachytherapy +/- XRT in 39 (66%). The Gleason score of the recurrence was 6, 7, 8-10 and not graded in 7, 40, 11 and 1, respectively. The pre-HDR median PSA was 4.13ng/mL (1.30–11.63). Twenty-five (42%) were staged with a PSMA PET scan. The median TV was 4.8mL (1.5-16.1). The median (IQR) dosimetric endpoints per implant were: CTV V13.5Gy 96.5% (95.1, 97.7), CTV D90 15.2Gy (14.6, 15.7), urethral