Impact of Prostate Cancer Treatment with Low Dose Rate Brachytherapy on Testosterone: A Retrospective Analysis

Abstract

Decrease in serum testosterone counts have been reported in the literature following external beam radiotherapy (EBRT), with a suggested association to low dose irradiation of the testes occurring with historical and modern external techniques. Low dose rate (LDR) brachytherapy has been described as exposing the testes to between 2 and 19 cGy compared with 196-220 cGy with EBRT. This decrease in excess dose is hypothesized to spare post-treatment testosterone decrease and subsequent change in patient-perceived quality of life. Here, we retrospectively evaluate LDR-treated prostate cancer patient testosterone change in a single-institution patient cohort. Patients with prostate cancer who had previously received LDR brachytherapy were identified, and patients with prior baseline total testosterone lab values as well as a lab value within one year post-treatment were identified. Patients receiving concurrent androgen deprivation therapy or EBRT were excluded. The closest baseline values prior to and after LDR treatment were used for before/after comparison. Samples were compared using the paired t-test. A total of 1,463 patients receiving LDR were identified with data available for analysis between 1998 and 2023; of these, 139 patients met the above criteria for analysis. Mean age was 66 (median 67; range: 47 - 79). 5 patients received 110 Gy, 2 received 120 Gy, and the remainder 145 Gy, all conducted with I-125. Total mCi delivered ranged from 20.3 mCi to 56.7 mCi (median 37.6 mCi). Approximately 57% were GS6, 42% G7, and < 1% G8. Approximately 80% of patients had T1c disease, with 19% T2 and < 1% T3a. All patients were cN0M0. Mean pre- and post-treatment testosterone were 385.5 ng/dL and 382.9 (SD: 170.9, 150.9; mean difference 2.65 [95% CI: -15.6, 20.9]), respectively, with no statistical change noted (p = 0.774). Testosterone levels have been reported to drop following definitive EBRT owing to excess dose delivery to the testes. On review of our institutional experience in definitive LDR brachytherapy for patients treated without ADT administration, no change in testosterone levels were noted.