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

Abstract

Stereotactic body radiotherapy (SBRT) is being increasingly utilized for the definitive treatment of low to intermediate risk prostate cancer. Sources of higher incidental testicular dose arises from the use of non-coplanar beams, larger scatter dose fractions, and increased frequency of image-guidance. There remains little knowledge of how testicular scatter dose during SBRT affects testicular function and sexual quality of life after treatment. Patients with low to intermediate risk prostate cancer who were enrolled in two multi-institutional prospective clinical trials evaluating prostate SBRT between 2009 and 2014 were identified. Pre- and post-treatment testosterone (T) values were available. Patient-reported quality of life measures were obtained via Expanded Prostate Composite Index-26 (EPIC) questionnaires. The median absolute and relative changes in T within 6 months, 12 months, and 24 months after completion of SBRT were compared to the median pre-treatment baseline using the Wilcoxon-Mann-Whitney test. Average pre- and post-treatment EPIC scores were compared using unpaired t-tests. A total of 77 patients were analyzed with up to 24 months of follow up. The median age was 70 with a median baseline pre-treatment T of 386 ng/dL. Within 6 months of completion of SBRT, the median T was 332 ng/dL, which corresponded to a statistically significant median decrease of 26 ng/dL (p < 0.01) and a median relative decrease of 7.6% (p < 0.01). At 12 months after SBRT, the median T was 345 ng/dL, which correlated with a statistically significant median decrease of 60 ng/dL (p < 0.01) and a median relative decrease of 15.3% (p < 0.01). By 2 years, the median T was 370 ng/dL, corresponding to a non-significant median decrease of 19.5 ng/dL (p = 0.30) and a median relative decrease of 5.3% (p = 0.30). The median EPIC sexual function scores pretreatment and within 6, 12, and 24 months after treatment were 63, 43 (p = 0.98), 47 (p = 0.98), and 63 (p = 0.36). The median EPIC hormone/vitality scores pretreatment and within 6, 12, and 24 months after treatment were 100, 95 (p = 0.21), 100 (p = 0.97), and 100 (p = 0.18). In this multi-institutional retrospective study of patients with low to intermediate risk prostate cancer who received prostate SBRT, we found a statistically significant decline in median T levels at 6 and 12 months after treatment although this change never reached any clinically significant hypogonadal state. By 24 months the median T levels were no longer significantly different from baseline. Despite the transient decline in median T levels there was no corresponding significant change in sexual function or hormone/vitality scores. Longer follow up is needed to confirm that low dose testicular scatter does not lead to any lasting or clinically consequential declines in T levels after prostate SBRT.