3227 - Placing the Pin Back into the Stone Cushion: A Salvage HDR Brachytherapy Experience

Purpose/Objective(s): Salvage brachytherapy has been shown to be a safe and efficacious treatment option for patients with locally recurrent prostate cancer following initial radiotherapy. A limited number of studies exist which address salvage high-dose rate brachytherapy (sHDRBT) regimens and outcomes. We retrospectively reviewed the sHDRBT delivered to patients at our institution in the reirradiation setting for prostate cancer to assess biochemical progression free survival (bPFS) at 2 years and the incidence of acute to subacute GI/GU toxicity.

Materials/Methods: This was a single institution retrospective analysis of patients treated with sHDRBT from 3/1/2017 to 1/4/2023. All patients had biopsy proven disease prior to treatment and received 24 Gy in 2 fractions delivered 7 days apart (range 5- 20 days). Patients with available post sHDRBT follow up data through 2 years were included. The Phoenix definition (nadir + 2 ng/ml) was used to define failure and the bPFS rate was estimated at two years following treatment using Kaplan Meier methodology. Toxicity was assessed using CTCAE criteria for reported GI or GU symptoms during treatment and at their first follow up visit (3-4 months after).

Results: Of the 60 patients treated during the observed time, a total of 47 patients were eligible for analysis and their initial radiation treatments were delivered from 1999-2019. Initial treatments included IMRT (49%), proton (19%), low-dose rate brachytherapy (LDRBT, 13%), 3DCRT (9%), SBRT (6%), unspecified EBRT (4%), and combined modality (2%). Local salvage therapy prior to sHDRBT occurred in 4 patients (3 cryoablation, 1 LDRBT). The majority of patients (70%) underwent a PET CT prior to sHDRBT and 9 patients (19%) received concurrent hormone therapy, defined as administration within three months of their salvage treatment. At 2 years, bPFS was 68% (95% CI 53-79). Of the 16 patients that failed, 4 patients were initiated on hormone therapy (due to rising PSA levels) before qualifying for defined biochemical failure. Freedom from biochemical failure did not appear to be affected by concurrent ADT use (89% concurrent vs. 71% without, p = 0.32). The anatomic location of the 16 total failures, determined by PET, were as follows: 10 local (prostate/seminal vesicle), 2 regional (lymph nodes), 2 locoregional, 1 local + distant (bone), and 1 regional + distant. 32 of the 47 patients had toxicity data available for analysis. Only 2 patients experienced one or more Grade 2 GI toxicity. 9 patients had one or more Grade 2 GU toxicity and 1 patient had a Grade 3 GU toxicity (nocturia).

Conclusion: Salvage HDRBT, delivered in 24 Gy over 2 fractions, is an effective reirradiation treatment option for patients with prostate cancer. Greater than two-thirds of patients are without biochemical failure at 2 years with minimal acute to subacute GI or GU toxicity.