PSMA PET/CT to evaluate response to SBRT for prostate cancer bone metastases

Background: In the current study we evaluated Ga-68 PSMA PET/CT to measure local control of bone metastasis in oligometastatic prostate cancer patients treated with SBRT. Materials and methods: After the institutional review board approval, a retrospective review of medical records of consecutive prostate cancer patients treated between 2014 and 2018 was conducted. Only medical records of patients that were treated with SBRT for bone metastasis and had pre-and post-SBRT Ga-68 PSMA PET/CT scans were included in our study. Data extracted from the medical files included patient-related (age), disease-related (Gleason score, site of metastasis), and treatment-related factors and outcomes. Results: During the study period, a total of 12 patients (15 lesions) were included, with a median age of 73 years. The median follow-up was 26.5 months (range 13-45 months). Median time Ga-68 PSMA PET/CT follow up was 17.0 months (range 3-39 months). The median pre-treatment PSA was 2 ng/mL (range 0.56-44 ng/mL) vs. post treatment PSA nadir of 0.01 ng/mL (0.01-4.32) with a median timeto nadir of 7 months (range, 2-12). Local control was 93% during the follow up period and there was correlation with PSMA avidity on PET. None patients developed recurrences in the treated bone. None of the patients had grade 3 or more toxicities during follow-up. Conclusions: SBRT is a highly effective and safe method for treatment of prostate cancer bone metastases. More studies are required to determine if SBRT provides greater clinical benefit than standard fractionation for oligometastatic prostate cancer patients. Ga-68 PSMA PET/CT should be further investigated for delineation and follow-up.