Proton Radiotherapy for Prostate Cancer is Not Associated with Post Treatment Testosterone Suppression

Abstract

Two independent studies of photon (x-ray) therapy for prostate cancer have demonstrated evidence of testosterone suppression after treatment. The current study was undertaken to determine if this is also the case with conformal protons. From August, 2006 to October, 2007, 173 patients with low and intermediate risk localized prostate cancer were enrolled on the PR01 (low risk) and PR02 (intermediate risk) protocols. Patients received between 78 and 82 Cobalt Gray Equivalent (CGE) at 2CGE per daily fraction to the prostate. No patient received pelvic nodal irradiation. 19 Patients were excluded from analysis who either: received androgen deprivation therapy at any time prior to radiotherapy (18); or who received androgen deprivation therapy after radiotherapy (1). Pretreatment serum testosterone levels are available for 134 (87 %) of the remaining 154 patients. 6 month post treatment serum testosterone is available for 117 patients and 12 month post treatment serum testosterone is available for 63 patients. Post treatment testosterone levels were compared with the pretreatment levels. At 6 months after proton therapy, when compared to baseline pretreatment values: mean serum testosterone increased by 9ng/dL or 2.4% of baseline; and median change in serum testosterone increased by 6ng/dL or 0.2% of baseline (p = 0.45). At 12 months after proton therapy, when compared to baseline pretreatment values: mean serum testosterone decreased by 2ng/dL or 0.6% of baseline; and median change in serum testosterone decreased by 16ng/dL or 4.7% of baseline (p = 0.99). Conformal proton therapy, as delivered on the PR01 and PR02 protocols did not appear to significantly impact serum testosterone levels. The wide range of testosterone levels seen both before and after treatment however suggest that other variables exert substantial influence on this particular laboratory value.