• Hitoshi Ishikawa, Hiroshi Tsuji, Tadashi Kamada, Naoki Hirasawa, Takeshi Yanagi, Jun-Estu Mizoe, Koichiro Akakura, Hiroyoshi Suzuki, Jun Shimazaki, Takashi Nakano, and Hirohiko Tsujii.
• Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
• Int. J. Radiat. Oncol. Biol. Phys. 2008 Sep 1; 72 (1): 78-84.

PurposeTo determine the risk factors for persistent late genitourinary (GU) morbidity after carbon ion radiotherapy (C-ion RT) for prostate cancer.Methods And MaterialsBetween 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).ResultsGrade 1 and 2 persistent GU toxicities developed in 36 (21%) and 3 (2%) patients, respectively. The use of long-course ADT (>or=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 (<24 months) had no effect on the development of toxicity (p = 0.35). The 5-year actuarial complication rate of 80 patients undergoing long-course ADT was 31.1%; the corresponding rate for the 92 patients who received no ADT or short-course ADT was 22.2%.ConclusionAdverse effects with long-course ADT on persistent GU morbidity were observed in this study. Additional investigation is needed to identify suitable ADT administration according to risk groups, but long-course ADT should not be adopted for non-high-risk prostate cancer patients to reduce the GU toxicity rate with C-ion RT.

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