Testosterone kinetics after proton therapy for low- and intermediate-risk prostate cancer.

237 Background: Evaluate long term changes in serum testosterone levels in patients with low and intermediate risk prostate cancer treated with proton therapy (PT) on two prospective clinical trials. Methods: Between August, 2006 and October, 2007, 171 patients with low and intermediate risk prostate cancer were enrolled and treated on the University of Florida Proton Therapy Institute institutional review board (IRB) approved PR01 and PR02 protocols. Of the 171 patients, 20 were excluded for having received hormonal therapy prior to PT. The pretreatment serum testosterone level was available for 149 of the remaining 151 patients. These 149 patients were included in the present study. Proton doses ranged from 78 Cobalt Gray Equivalent (CGE) to 82 CGE to the prostate using passively scattered protons. No patient underwent pelvic nodal irradiation. Results: The median baseline serum testosterone level was 358ng/dL (range 112 to 791ng/dL). Immediately after completion of PT, median serum testosterone was 365ng/dL which was not significantly different from the pre-PT level (p=0.2039). Subsequent median testosterone levels with associate P-Values are shown in the Table. At no point in the 60 month follow up period was the median serum testosterone value significantly different from the baseline value. Conclusions: Conformal proton therapy to the prostate, as delivered using the University of Florida Proton Therapy Institute PR01 and PR02 protocols, did not appear to significantly affect serum testosterone levels within 60 months after PT. [Table: see text]