Testosterone Levels and Sexual Quality of Life After Stereotactic Body Radiation Therapy for Prostate Cancer: A Multi-Institutional Analysis of Prospective Trials.

Purpose: The impact of higher scatter doses per fraction on testicular function and quality of life after prostate stereotactic body radiation therapy (SBRT) is poorly studied.

Methods And Materials: Six hundred thirty-six patients treated with SBRT for low- to intermediate-risk prostate cancer from 2009 to 2014 were included. Changes in testosterone and in sexual and hormonal domain scores on the Expanded Prostate Cancer Index Composite-26 (EPIC) questionnaire over a 24-month period were evaluated via a 1-sided t test. EPIC score changes were evaluated in comparison with a distribution-based minimal clinically important difference threshold, wherein changes of greater than one half or greater than one third of the standard deviation in each domain were considered as medium-sized or small-sized effects, respectively.

Results: Median and mean percent changes in testosterone at the 3- to 6-month, 7- to 12-month, 13- to 18-month, and 19- to 24-month time periods were -13.41% and -4.49% (P = .02); -12.23% and -2.77% (P = .13); -11.20% and -0.29% (P = .47); -5.00% and + 1.20% (P = .65). When analyzed after dividing the cohort into 3 groups based on baseline testosterone values using tertiles, testosterone tended to increase in patients in the first group and decrease in patients in the third group. Overall, the decline in EPIC hormonal domain scores never exceeded the threshold for a small-sized effect, though the decline in EPIC sexual domain scores did pass this threshold at the 19- to 24-month time period (mean 10.90 point decline). This decline was not present when groups were examined individually.

Conclusions: In this large cohort of prospectively followed patients, there was a transient decline in testosterone shortly after SBRT that normalized by 24 months posttreatment. There was no significant change in EPIC hormonal domain scores. A significant decline in EPIC sexual domain scores, consistent with a small-sized clinically detectable difference, manifested between 19 and 24 months of follow-up. These results are consistent with testosterone decline patterns and sexual function changes seen after other forms of photon-based radiation therapy.