Objectives: To report the outcomes of stereotactic ablative body radiotherapy (SABR) in men with oligometastatic prostate cancer (PCa) diagnosed on prostate-specific membrane antigen (PSMA)-positron emission tomography/computed tomography (PET/CT), based on a single-institution experience and the published literature.
Patients and methods: This was a retrospective cohort study of the first 20 consecutive men with oligometastatic PCa, treated with SABR in a single institution, who had biochemical recurrence after previous curative treatment (surgery/radiotherapy), had no evidence of local recurrence, were not on palliative androgen deprivation therapy (ADT), and had PSMA-PET/CT-confirmed oligometastatic disease (≤3 lesions). These men were treated with SABR to a dose of 30 Gy in three fractions for bone metastases, and 35-40 Gy in five fractions for nodal metastases. The outcomes of interest were: PSA response; local progression-free survival (LPFS); distant progression-free survival (DPFS); and ADT-free survival (ADTFS). A literature review was performed to identify published studies reporting on outcomes of PSMA-PET/CT-guided SABR.
Results: In our institutional cohort, 12 men (60%) had a decline in PSA post-SABR. One man had local progression 9.6 months post-SABR, with 12-month LPFS of 93%. Ten men had distant progression outside of their SABR treatment field, confirmed on PSMA-PET/CT, with 12-month DPFS of 62%, of whom four were treated with palliative ADT, two received prostate bed radiotherapy for prostate bed progression (confirmed on magnetic resonance imaging), and four received a further course of SABR (of whom one had further progression and was treated with palliative ADT). At last follow-up, six men (one with local progression and five with distant progression) had received palliative ADT. The 12-month ADTFS was 70%. Men with longer intervals between local curative treatment and SABR had better DPFS (P = 0.03) and ADTFS (P = 0.005). Four additional studies reporting on PSMA-PET/CT-guided SABR for oligometastatic PCa were identified and included in the review, giving a total of 346 patients. PSA decline was reported in 60-70% of men post-SABR. The 2-year LPFS, DPFS and ADTFS rates were 76-100%, 27-52%, and 58-62%, respectively.
Conclusion: Our results showed that PSMA-PET/CT could have an important role in identifying men with true oligometastatic PCa who would benefit the most from metastases-directed therapy with SABR.
Keywords: PSMA PET; #PCSM; #prostatecancer; metastatic directed treatment; oligometastases; prostate cancer; stereotactic radiotherapy.
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