PSOR08 Presentation Time: 12:05 PM

• Published in: Brachytherapy Vol. 23; no. 6; pp. S83 - S84
• Main Authors: Chung, Hans, MD, Hudson, John, MD, Loblaw, Andrew, MD, Tseng, Chia-Lin, MD, Paudel, Moti, PhD, Davidson, Melanie, PhD, Wronski, Matt, PhD, Haider, Masoom, MD, Deabreu, Andrea, BSc, Morton, Gerard, MD
• Format: Journal Article
• Language: English
• Published: 01.11.2024
• Subjects: Hematology, Oncology, and Palliative Medicine; Radiology
• ISSN: 1538-4721
• DOI: 10.1016/j.brachy.2024.08.118

PurposeSalvage high dose rate (HDR) prostate brachytherapy is a treatment option for intra-prostatic recurrent localized prostate cancer after prior radiation. Recently, our center reported the outcomes of two companion prospective phase 2 studies of MR-assisted salvage HDR prostate brachytherapy: whole-gland (WG) with an intra-prostatic boost, and focal-gland (FG). Both studies mandated post-salvage multiparametric MRI (mpMRI). This study explores the subsequent relapse pattern and dosimetry of the patients who had recurrent/persistent disease on post-salvage mpMRI. Materials and MethodsEligible patients had biopsy confirmed localized prostate cancer who relapsed >30 months after primary brachytherapy and/or external radiotherapy with a negative metastatic workup and IPSS <15. Ultrasound (US)-based HDR brachytherapy with cognitive fusion initially then subsequently contour-based deformable registration between the diagnostic mpMRI and ultrasound images was performed. For FG salvage brachytherapy, the prescription dose was 27Gy in 2 fractions, 1-2 weeks apart, to the dominant intra-prostatic lesion (DIL) with a 3-5mm expansion. For WG salvage brachytherapy, the prescription dose was 21Gy to the entire prostate and 27Gy to the MR-defined DIL divided over two implants (3-5mm expansion) separated by 1-2 weeks. The urethra and rectal dose constraints were prioritized over dose coverage of the DIL. All patients underwent pre- and 1-2 year post-salvage mpMRI to assess response. Adjuvant androgen deprivation therapy (ADT) was not used. For the subset of patients who had recurrent/persistent disease on the post-salvage mpMRI (PIRADS≥4), we determined the patterns of recurrence and the dosimetry of the salvage HDR brachytherapy to those sites. Post-salvage biopsies were not mandated in the protocol. Deformable registration between the post-salvage DIL and the original plan was performed using MIMvista software to calculate the received dosimetry of the treated site, and identify geometric patterns of recurrence. ResultsSixty patients (median 73 years) were treated with salvage HDR (WG n=30, FG n=30). The primary radiation for the WG cohort was 70-78Gy with conventional fractionation in 28 patients and alternate fractionation in 2 patients (35Gy/5F and 50Gy/15F). The primary radiation for the FG cohort was 70-78Gy with conventional fractionation (n=15), 19Gy/1F HDR monotherapy (n=9), 15Gy/1F HDR boost plus 37.5Gy/15F (n=2), 105Gy/1F LDR boost plus 45Gy/30F (n=1) and 145Gy/1F LDR monotherapy (n=3). For both cohorts, the overall median (range) pre-salvage HDR PSA was 4.24 (0.63-11.63). The post-salvage mpMRI (median 429 days) was performed in 27 and 28 patients who had FG and WG, respectively. It identified 16 recurrent/persistent lesions: WG: n = 9 (in-field = 6, marginal = 3, distant = 0); FG: n=7 (in-field = 3, marginal = 3, distant = 1). The dosimetry received by the area of post-salvage recurrent/persistent is summarized in the Table. ConclusionsOur results of salvage FG and WG brachytherapy suggest that most recurrent/persistent lesions seen on the post-salvage mpMRI were infield, despite optimal dosimetric coverage (V27, D90, D98). Alternate strategies for treatment intensification may be considered. Marginal recurrences were undercovered and may suggest inadequate margins. Distant intra-prostatic recurrence was minimal in both cohorts, though this was likely limited by the timing of the mpMRI at 1-2 years post-salvage.