Stereotactic Body Radiotherapy for Oligometastatic Prostate Cancer Detected via Prostate-specific Membrane Antigen Positron Emission Tomography

Background: The management of oligometastatic prostate cancer (PCa) remains controversial, especially following the introduction of prostate-specific membrane antigen (PSMA) positron emission tomography (PET) imaging.

Objective: To assess whether stereotactic body radiotherapy (SBRT) provides a potential for cure in a selected group of patients with oligometastatic PCa in the PSMA-PET era.

Design, setting, and participants: This was a prospective, single-centre study of patients with oligometastatic PCa undergoing SBRT from November 2014 to July 2016. We included patients with relapsed PCa receiving SBRT with PSMA-PET-confirmed oligometastases (n=1-3) confined to lymph nodes (LNs) or bone without androgen deprivation therapy. SBRT schedules included 20Gy/1# or 24Gy/2# to bone metastases, and 50Gy/5# or 30Gy/3# to LNs.

Outcome measurements and statistical analysis: The primary endpoint was biochemical failure (BF) defined as a prostate-specific antigen (PSA) level of nadir + 0.2 ng/ml following SBRT.

Results and limitations: Fifty-seven patients were eligible, of whom 50 (88%) had undergone radical prostatectomy. The median time from definitive treatment to SBRT was 5.6 yr. A total of 73 lesions were treated: 44 patients had one metastasis, while 13 had two or three. Thirty-seven patients (65%) had LN-only disease, while 18 (31%) had bone-only metastasis. Median follow up was 16 mo. The median biochemical disease-free survival (bDFS) for the cohort was 11 mo, with 31.9% bDFS at 15 mo. All patients with BF (n=43) underwent a repeat PSMA-PET scan, which revealed no in-field failures. Median bDFS was not affected by prostate-specific antigen (PSA) at diagnosis, Gleason score, time from diagnosis to SBRT, site (bone vs LN), PSA doubling time before SBRT, or number of metastases. Failures were somewhat less common in patients with low PSA before SBRT. Toxicity was rare: no patients developed grade ≥2 late toxicity.

Conclusions: SBRT delivered very high rates of local control with minimal toxicity. However, distant recurrences occurred in most patients by 15 mo and did not appear to be predicted by known prognostic factors.

Patient summary: In this report, we looked at outcomes after the use of stereotactic body radiotherapy for patients with prostate cancer spread to one to three lymph nodes or bones as detected by positron emission tomography scans. We demonstrated high rates of control of the treated lesions with low toxicity, but by 15 mo more than two-thirds of patients had developed recurrent cancer outside the treated area.