Stereotactic body radiation therapy for the primary treatment of localized prostate cancer

Objective The low alpha/beta ratio of prostate cancer suggests that hypofractionated schemes of dose-escalated radiotherapy should be advantageous. We report our experience using stereotactic body radiation therapy (SBRT) for the primary treatment of prostate cancer to assess efficacy and toxicity. Methods From 2007 to 2010, 70 patients (51 % low risk, 31 % intermediate risk, and 17 % high risk) with localized prostate cancer were treated with SBRT using the CyberKnife system. One-third of patients received androgen deprivation therapy. Doses of 37.5 Gy (n=29), 36.25 Gy (n=36), and 35 Gy (n=5) were administered in five fractions and analyzed as high dose (37.5 Gy) vs. low dose (36.25 and 35 Gy). Results At a median 27 and 37 months follow-up, the low and high dose groups' median PSA nadir to date was 0.3 and 0.2 ng/ml, respectively. The 3-year freedom from biochemical failure (FFBF) was 100 %, 95.0 % and 77.1 % for the low-, intermediate-and high-risk patients. A dose response was observed in intermediate-and high-risk patients with 72 % vs. 100 % 3-year FFBF for the low and high dose groups, respectively (p=0.0363). Grade III genitourinary toxicities included 4 % acute and 3 % late (all high dose). Potency was preserved in 83 % of hormone naive patients. Conclusion CyberKnife dose escalated SBRT for low-, intermediate-and high-risk prostate cancer exhibits favorable efficacy with acceptable toxicity.