Early outcomes following local salvage treatment with MRI-assisted low-dose rate brachytherapy (MARS) for MRI-visible postsurgical bed recurrences and focal intraprostatic recurrences.

Background: To determine outcomes of MRI-assisted radiosurgery (MARS) for salvage brachytherapy using the radioisotope Pd after various upfront treatments including surgery, external beam radiotherapy, and brachytherapy.

Methods: We retrospectively reviewed data for patients who underwent salvage MARS for intraprostatic lesions or prostate bed recurrences from 2016 to 2022. Biochemical recurrence, prostate cancer-specific, and overall survival, and the cumulative incidences of toxicities, were determined by Kaplan-Meier estimates. Cox proportional hazards models were used to determine associations between clinical and treatment variables and risk of toxicity.

Results: Study included 31 patients with local recurrence after initial definitive treatment. Four (13%) were initially treated with prostatectomy and salvage radiation, twenty-four (77%) with external beam radiation, and three with brachytherapy. Most had intermediate- or high-risk prostate cancer at the time of diagnosis. Twenty-two patients (71%) had focal-gland and nine (29%) had whole-gland MARS LDR salvage brachytherapy. Median follow-up was 35-28 months. By last follow-up, 5 patients (16%) experienced recurrence and started ADT, 3 patients started ADT before experiencing recurrence due to physician discretion, and 23 patients (74%) remained without recurrence. No patients died of prostate cancer. Median PSA nadir for recurrence-free patients was 0.2 ng/mL (range, 0-0.9 ng/mL). Grade 3 toxicities occurred in 4 patients (13%) including 3 patients (13%) with genitourinary events only and 1 patient (3%) with both a grade 3 genitourinary and a grade 3 gastrointestinal event.

Conclusions: In this modern series of patients undergoing salvage MARS with Pd, we observed acceptable toxicity and early, promising biochemical disease control. These findings highlight the broader applicability of salvage MARS regardless of upfront treatment modality.