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 ¹⁰³Pd 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 ¹⁰³Pd, we observed acceptable toxicity and early, promising biochemical disease control. These findings highlight the broader applicability of salvage MARS regardless of upfront treatment modality.