Stereotactic Radiation Therapy for Localized Prostate Cancer: 10-Year Outcomes From Three Prospective Trials

SABR is growingly accepted for the treatment of localized prostate cancer with recent randomized trials showing noninferiority compared with conventional or moderately hypofractionated radiation therapy. The natural history of prostate cancer necessitates extended surveillance for recurrence; however, there are a few prospective studies reporting long-term outcomes.

This study included patients with low- and intermediate-risk localized prostate cancer from 3 Canadian clinical trials enrolled from 2006 to 2013. All patients received SABR to the prostate consisting of 35 to 40 Gy in 5 fractions over 11 to 29 days. Prostate specific antigen, distant metastasis, and vital status were prospectively recorded. The occurrence of a second malignancy after treatment was assessed by a chart review and classified using modified Cahan's criteria.

Two hundred sixty-seven patients were included. Median follow-up was 10.3 years (interquartile range, 7.8-12.7). Ten-year biochemical failure (95% confidence interval) was 7.7% (3.9%-11.5%); 10-year overall survival, prostate cancer-specific survival, and freedom from metastasis were 84.1% (79.3%-89.1%), 99.2% (98.1%-100%), and 98.8% (97.5%-100%), respectively. Twenty-seven of 267 (10.1%) patients experienced a second malignancy (SM), with 6/27 patients (22.2%) classified as having a SM likely (n = 3) or possibly (n = 3) related to prior radiation therapy. Ten-year freedom from SM was 89.2%.

SABR shows excellent long-term disease control for low- and intermediate-risk localized prostate cancer. Patients treated for prostate cancer have a moderate risk of SM, consistent with background rates for the population.