PSMA-guided metastases directed therapy for bone castration sensitive oligometastatic prostate cancer: a multi-institutional study

Abstract

To assess the outcomes of a cohort of bone oligometastatic prostate cancer patients treated with PSMA-PET guided stereotactic body radiotherapy (SBRT). From April 2017 to January 2021, 40 patients with oligorecurrent prostate cancer detected by PSMA-PET were treated with SBRT for bone oligometastases. Concurrent androgen deprivation therapy was an exclusion criterion. A total of 56 prostate cancer bone oligometastases were included in the present analysis. In 28 patients (70%), oligometastatic disease presented as a single lesion, two lesions in 22.5%, three lesions in 5%, four lesions in 2.5%. 30.3% were spine-metastases, while 69.7% were non-spine metastases. SBRT was delivered for a median dose of 30 Gy (24-40 Gy) in 3-5 fractions, with a median EQD₂ = 85 Gy₂ (64.3-138.9Gy₂). With a median follow-up of 22 months (range 2-48 months), local control (LC) 1- and 2-years rates were 96.3% and 93.9%, while distant progression-free survival (DPFS) rates were 45.3% and 27%. At multivariate analysis, the lower PSA nadir value after SBRT remained significantly related to better DPFS rates (p = 0.03). In 7 patients, a second SBRT course was proposed with concurrent ADT, while 11 patients, due to polymetastatic spread, received ADT alone, resulting in 1- and 2-years ADT-free survival rates of 67.5% and 61.8%. At multivariate analysis, a lower number of treated oligometastases maintained a correlation with higher ADT-free survival rates (p = 0.04). In our experience, PSMA-PET guided SBRT resulted in excellent results in terms of clinical outcomes, representing a helpful tool with the aim to delay the start of ADT.

Keywords: Oligometastases; PSMA-PET; Stereotactic body radiotherapy.