Stereotactic body radiotherapy for localized prostate cancer: pooled analysis from a multi-institutional consortium of prospective phase II trials.

PURPOSE The effectiveness of stereotactic body radiotherapy (SBRT) for localized prostate cancer is tested. METHODS AND MATERIALS A total of 1100 patients with clinically localized prostate cancer were enrolled in separate prospective phase 2 clinical trials of SBRT from 8 institutions during 2003-11 and pooled for analysis. SBRT using the CyberKnife delivered a median dose of 36.25Gy in 4-5 fractions. Patients were low-risk (58%), intermediate-risk (30%) and high-risk (11%). A short-course of androgen deprivation therapy (ADT) was given to 14%. PSA relapse defined as a rise >2ng/ml above nadir was analyzed with the Kaplan Meier method. RESULTS With a median follow-up of 36months there were 49 patients with PSA failure (4.5%), 9 of whom were subsequently determined to be benign PSA bounces. The 5-year biochemical relapse free survival (bRFS) rate was 93% for all patients; 95%, 83% and 78% for GS ⩽6, 7 and ⩾8, respectively (p=0.001), and 95%, 84% and 81% for low-, intermediate- and high-risk patients, respectively (p<0.001). No differences were observed with ADT (p=0.71) or as a function of total dose (p=0.17). A PSA bounce of >0.2ng/ml was noted among 16% of patients. For 135 patients possessing a minimum of 5years follow-up, the 5-year bRFS rate for low- and intermediate-risk patients was 99% and 93%, respectively. CONCLUSION PSA relapse-free survival rates after SBRT compare favorably with other definitive treatments for low and intermediate risk patients. The current evidence supports consideration of SBRT among the therapeutic options for these patients.