Stereotactic body radiation therapy (SBRT) for prostate cancer in men with large prostates (≥50 cm3)

Background: Patients with large prostate volumes have been shown to have higher rates of genitourinary and gastrointestinal toxicities after conventional radiation therapy for prostate cancer. The efficacy and toxicity of stereotactic body radiation therapy (SBRT), which delivers fewer high-dose fractions of radiation treatment, is unknown for large prostate volume prostate cancer patients. We report our early experience using SBRT for localized prostate cancer in patients with large prostate volumes. Methods: 57 patients with prostate volumes >= 50 cm(3) prior to treatment with SBRT for localized prostate carcinoma and with a minimum follow up of two years were included in this retrospective review of prospectively collected data. Treatment was delivered using Cyberknife (Accuray) with doses of 35-36.25 Gy in 5 fractions. Biochemical control was assessed using the Phoenix definition. Toxicities were scored using the CTCAE v.4. Quality of life was assessed using the American Urological Association (AUA) Symptom Score and the Expanded Prostate Cancer Index Composite (EPIC)-26. Results: 57 patients (23 low-, 25 intermediate- and 9 high-risk according to the D'Amico classification) at a median age of 69 years (range, 54-83 years) received SBRT with a median follow-up of 2.9 years. The median prostate size was 62.9 cm(3) (range 50-138.7 cm(3)). 33.3% of patients received ADT. The median pre-treatment prostate-specific antigen (PSA) was 6.5 ng/ml and decreased to a median PSA of 0.4 ng/ml by 2 years (p <0.0001). A mean baseline AUA symptom score of 7.5 significantly increased to 13 at 1 month (p = 0.001) and returned to baseline by 3 months (p = 0.21). 23% of patients experienced a late transient urinary symptom flare in the first two years following treatment. Mean baseline EPIC bowel scores of 95.8 decreased to 78.1 at 1 month (p <0.0001), but subsequently improved to 93.5 three months (p = 0.08). The 2-year actuarial incidence rates of GU and GI toxicity >= grade 2 were 49.1% and 1.8%, respectively. Two patients (3.5%) experienced grade 3 urinary toxicity, and no patient experienced grade 3 gastrointestinal toxicity. Conclusions: SBRT for clinically localized prostate cancer was well tolerated in men with large prostate volumes.