Adverse Effects of Androgen Deprivation Therapy on Persistent Genitourinary Complications After Carbon Ion Radiotherapy for Prostate Cancer

Purpose To determine the risk factors for persistent late genitourinary (GU) morbidity after carbon ion radiotherapy (C-ion RT) for prostate cancer. Methods and Materials Between April 2000 and November 2003, a Phase II study of 175 prostate cancer patients was performed to assess C-ion RT with a dose fractionation (66 Gray equivalent in 20 fractions) established from previous Phase I-II studies. The effects of the clinical and dosimetric parameters on the occurrence of persistent GU toxicity in 172 patients who survived for >18 months after C-ion RT were examined retrospectively. C-ion RT alone was performed for 33 low-risk patients, and 139 high-risk patients received C-ion RT combined with androgen deprivation therapy (ADT). Results Grade 1 and 2 persistent GU toxicities developed in 36 (21%) and 3 (2%) patients, respectively. The use of long-course ADT (≥24 months) and acute GU toxicity were associated with the occurrence of persistent toxicity by multivariate analysis ( p = 0.016 and p = 0.048, respectively), but short-course ADT (