Stereotactic body radiotherapy for high-risk prostate cancer (5 treatment days): Toxicity results of a phase II trial

46 Background: Stereotactic body radiotherapy (SBRT) for high-risk prostate cancer (CaP) remains investigational not only due to undetermined efficacy but also due to concerns for the potential toxicity when the treatment volumes extend beyond the prostate gland itself. Methods: Men with high-risk CaP, as defined by Gleason score > = 8, clinical stage T3-T4, or initial PSA > = 20 ng/mL, were enrolled on a multicenter phase II trial and were treated with 40 Gy to prostate and 25 Gy to pelvic nodes in 5 fractions and 9 months neoadjuvant and concurrent ADT. Treatment with ADT and pelvic nodal radiation was at the discretion of the treating physician. Follow-up assessment was with CTCAE v4 and Expanded Prostate Composite Index (EPIC). Results: A total of 61 patients were treated, with a median follow-up of 12 months. Forty (64.4%) received ADT and 23 (37.1%) received nodal radiation. The median initial PSA was 8.1 ng/mL and 8% of patients had clinical T3-T4 disease; 45.9% and 39.3% had Gleason score 8 and 9-10 disease, respectively. No grade 3 or higher toxicities were seen. Rates of acute and late grade 2 genitourinary toxicities were 13.1% and 6.7%, respectively; rates of acute and late grade 2 gastrointestinal toxicities were 6.6% and 8.2%, respectively. Mean changes in EPIC urinary incontinence, urinary obstructive, and bowel domain scores at 4 months were -0.35, +1.44, and -2.38, respectively. For the 32 patients with evaluable EPIC scores at 12 months, mean changes on EPIC urinary incontinence, urinary obstructive, and bowel domain scores at 4 months were -1.04, -2.70, and -6.76, respectively. The percentages of patients with minimum clinically important change in EPIC urinary incontinence, urinary obstructive, and bowel domain scores at 4 months were 11.9%, 21.4%, and 26.2%, respectively. At 12 months, these figures were 13.9%, 30.6% and 27.8%. The receipt of ADT and/or nodal radiation had no significant effect on either physician- or patient-reported toxicity profiles (p > 0.1, Fisher’s exact test). Conclusions: SBRT regimens can be safely utilized to deliver the entire course in 5 treatment days in patients with high-risk localized CaP. Clinical trial information: NCT02296229.