Oligometastatic prostate cancer: An evaluation of stereotactic body radiotherapy (SBRT) as an alternative to palliative androgen deprivation therapy.

Abstract

229 Background: Oligometastatic prostate cancer (OPC) can be defined as 1-3 sites of metastasis, typically occurring some years after radical treatment for primary disease. Standard treatment is long-term palliative androgen deprivation therapy (ADT). Although effective, this treatment can have a significant impact on quality of life. We hypothesized that ablative treatment with SBRT may delay disease progression, and therefore the need for palliative ADT. Methods: A single-institution case series 2011-present. Eligible patients had metachronous OPC diagnosed by F-choline PET/CT and were ADT-naïve in the palliative setting. Stereotactic body radiotherapy was given to a dose of 30 Gy in 3 fractions using a robotic radiosurgery system (Cyberknife). ADT-free survival was calculated as the time from completion of treatment for oligometastatic disease to initiation of ADT with palliative intent. Follow up with clinical review and PSA was undertaken at four weeks, then three monthly, with F-choline PET/CT restaging as indicated. Palliative ADT was initiated for metastatic disease not amenable to further SBRT. Results: Twenty one patients received SBRT for ADT-naïve OPC. Median time from primary treatment to oligometastatic relapse was 59.7 months. Median PSA doubling time was 4.1 months. Six patients received a short course (3-6 months) of ADT with SBRT. Sites treated: bone (8) and lymph node (20). At a median follow up of 16.7 months, 81% (17) remained ADT-free. Median ADT-free survival was 28 months (95% CI: 10 - 43 months). All but one patient had a PSA response, with a median reduction of 84%. There were no local failures. Incidence of grade 1 and 2 CTCAE toxicity was 29% (6) and 5% (1), respectively. No toxicity of grade 3 or above was observed. Conclusions: SBRT for OPC is well tolerated. A clinically significant delay in initiation of palliative ADT was observed in patients with ADT-naïve oligometastatic disease. In view of this potential to improve patients’ quality of life, randomised trials against a standard of care are justified.