Proton radiotherapy for prostate cancer is not associated with post-treatment testosterone suppression

Three independent studies of photon (x-ray) radiotherapy (RT) for prostate cancer have demonstrated evidence of testosterone suppression after treatment. The present study was undertaken to determine whether this would also be the case with conformal protons.

Between August 2006 and October 2007, 171 patients with low- and intermediate-risk prostate cancer were enrolled and underwent treatment according to the University of Florida Proton Therapy Institute institutional review board-approved PR01 and PR02 protocols. Of the 171 patients, 18 were excluded because they had received androgen deprivation therapy either before (n = 17) or after (n = 1) RT. The pretreatment serum testosterone level was available for 150 of the remaining 153 patients. These 150 patients were included in the present study. The post-treatment levels were compared with the pretreatment levels.

The median baseline pretreatment serum testosterone level was 357.9 ng/dL. The median post-treatment testosterone value was 375.5 ng/dL at treatment completion (p = .1935) and 369.9 ng/dL (p = .1336), 348.7 ng/dL (p = .7317), 353.4 ng/dL (p = .6996), and 340.9 ng/dL (p = .1669) at 6, 12, 18, and 24 months after proton therapy, respectively.

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 the serum testosterone levels within 24 months after RT.