What happens to testosterone after prostate radiation monotherapy and does it matter?

There is uncertainty in the literature regarding the extent and relevance of temporary decreases in testosterone levels which occur after external radiation therapy for prostate cancer. We describe the phenomenon in detail and assess the impact on biochemical control and prostate specific antigen (PSA) doubling time in patients with relapse.

A total of 666 men were followed after external beam radiation without neoadjuvant or adjuvant androgen ablation. Serial testosterone and PSA were measured before and at 3 to 6-month intervals after therapy.

At a median nadir time of 6 months testosterone decreased to an average of 83% of baseline. Of the patients 7.5% experienced a decrease greater than 50%. All but 3% of those with normal initial testosterone levels experienced recovery to at least normal levels but only 60% had recovery to their individual pretreatment level. Multivariate analysis showed that patients with a low pre-intervention testosterone level, and those treated with larger radiation volumes had a lower testosterone nadir. In regard to biochemical control rates, initial testosterone level, degree of decrease, and absolute testosterone nadir had no effect in either univariate or multivariate analysis. PSA doubling times in patients with relapse were no different than in those with a small or larger testosterone decrease.

Temporary testosterone decrease after radiation therapy to the prostate is a real phenomenon with no impact on subsequent tumor outcomes.