Hypofractionated simultaneous integrated boost (IMRT-SIB) with pelvic nodal irradiation and concurrent androgen deprivation therapy for high-risk prostate cancer: results of a prospective phase II trial.

OBJECTIVE: The approach for treating high-risk prostate cancer still presents different unresolved issues. We report the safety and efficacy of a radiation therapy strategy based on the combination of moderate hypofractioned simultaneous integrated boost (SIB) and Image Guidance.

MATERIALS AND METHODS: In this phase II trial of patients with high-risk prostate cancer, Image Guided SIB-IMRT plans (Simultaneous Intensity Modulated - Intensity Modulated Radiotherapy) were delivered between 2009 and 2012. All patients enrolled (41) received in 25 fractions a total dose of 67.5 Gy (2.7 Gy/fraction) to the prostatic volume, 56.25 Gy (2.25 Gy/fraction) to the seminal vescicles, and 50 Gy (2.0 Gy/fraction) to the pelvic lymph nodes (LN) chains with concurrent androgen deprivation therapy (ADT). The image-guided radiotherapy (IGRT) procedure was performed using three gold seeds. RTOG late gastrointestinal and genitourinary toxicities and 6-year biochemical relapse-free survival (BRFS) were assessed in combination of their statistical correlation with clinical factors and dosimetric parameters.

RESULTS: Rate of late genitourinary toxicity grade 2 was 9.8%, while rates of late gastrointestinal toxicity were 14.6% and 2.4%, for grade 1 and 2, respectively. Diabetes and maximum doses to rectum appeared to be statistically relevant risk factors for late rectal toxicity. Five-year BRFS was 95.1%.

CONCLUSIONS: In our study, we observed positive results in terms of toxicity and good efficacy in a cohort of high-risk prostate cancer patients treated with a multimodality therapy approach comprising hypofractionation, irradiation of pelvic nodes (common iliac nodes included), and concurrent ADT. These favorable results may merit further investigation in a phase III randomized trial to confirm that whole pelvic radiation therapy (WPRT) combined with moderate hypofractionation and ADT could be performed safely and effectively.