Low incidence of new biochemical and clinical hypogonadism following hypofractionated stereotactic body radiation therapy (SBRT) monotherapy for low- to intermediate-risk prostate cancer

Abstract

BackgroundThe CyberKnife is an appealing delivery system for hypofractionated stereotactic body radiation therapy (SBRT) because of its ability to deliver highly conformal radiation therapy to moving targets. This conformity is achieved via 100s of non-coplanar radiation beams, which could potentially increase transitory testicular irradiation and result in post-therapy hypogonadism. We report on our early experience with CyberKnife SBRT for low- to intermediate-risk prostate cancer patients and assess the rate of inducing biochemical and clinical hypogonadism.MethodsTwenty-six patients were treated with hypofractionated SBRT to a dose of 36.25 Gy in 5 fractions. All patients had histologically confirmed low- to intermediate-risk prostate adenocarcinoma (clinical stage ≤ T2b, Gleason score ≤ 7, PSA ≤ 20 ng/ml). PSA and total testosterone levels were obtained pre-treatment, 1 month post-treatment and every 3 months thereafter, for 1 year. Biochemical hypogonadism was defined as a total serum testosterone level below 8 nmol/L. Urinary and gastrointestinal toxicity was assessed using Common Toxicity Criteria v3; quality of life was assessed using the American Urological Association Symptom Score, Sexual Health Inventory for Men and Expanded Prostate Cancer Index Composite questionnaires.ResultsAll 26 patients completed the treatment with a median 15 months (range, 13-19 months) follow-up. Median pre-treatment PSA was 5.75 ng/ml (range, 2.3-10.3 ng/ml), and a decrease to a median of 0.7 ng/ml (range, 0.2-1.8 ng/ml) was observed by one year post-treatment. The median pre-treatment total serum testosterone level was 13.81 nmol/L (range, 5.55 - 39.87 nmol/L). Post-treatment testosterone levels slowly decreased with the median value at one year follow-up of 10.53 nmol/L, significantly lower than the pre-treatment value (p < 0.013). The median absolute fall was 3.28 nmol/L and the median percent fall was 23.75%. There was no increase in biochemical hypogonadism at one year post-treatment. Average EPIC sexual and hormonal scores were not significantly changed by one year post-treatment.ConclusionsHypofractionated SBRT offers the radiobiological benefit of a large fraction size and is well-tolerated by men with low- to intermediate-risk prostate cancer. Early results are encouraging with an excellent biochemical response. The rate of new biochemical and clinical hypogonadism was low one year after treatment.

Hypofractionated stereotactic body radiation therapy as monotherapy for intermediate-risk prostate cancer

“…As previously reported, low grade urinary and rectal toxicities were common following prostate SBRT [28]. The most common urinary toxicities were frequency and urinary obstructive symptoms.…”

“…The QOL data indicate that CK monotherapy is well tolerated, with declines in patient reported urinary, bowel and sexual function that are similar to those seen in low-risk patients treated with CK SBRT monotherapy, [28] and comparable to the trends seen with conventionally fractionated external beam radiotherapy and brachytherapy [45-47]. Urinary symptoms peaked in the 1–2 weeks after SBRT, and were generally followed by improvement to pre-treatment levels within 2–3 months.…”

A single-center study of 100 consecutive patients with localized prostate cancer treated with stereotactic body radiotherapy

“…Oermann et al [30] have published a study on 26 patients treated with CK-SBRT, where serum testosterone levels and endocrine changes were observed: a small decline in total testosterone levels without the endocrine changes, typical of hypogonadism, was reported.…”

Stereotactic body radiotherapy for prostate cancer: ready for prime time?

“…While testosterone levels were not specifically measured, no clinical symptoms of hormone ablation were observed in any of the 304 patients treated. Oermann et al [76] recently published a study of 26 patients treated with CyberKnife SBRT to a total dose of 36.25 Gy in five fractions. They reported a median baseline serum testosterone level of 13.81 nmol/L with a clinically insignificant decline to a median level of 10.53 nmol/L at 1 year.…”