Radiotherapy for prostate cancer and sexual functioning

Radiation-induced erectile dysfunction using prostate-confined modern radiotherapy in a rat model

INTRODUCTION

The mechanisms of radiation-induced erectile dysfunction (ED) are unclear, as clinical studies are limited, and previous animal models were based on wide-field irradiation, which does not model current radiotherapy (RT) techniques.

AIMS

To perform functional and morphological analyses of erectile function (EF) utilizing image-guided stereotactic prostate-confined RT in a rat model.

METHODS

Sixty young adult male rats aged 10-12 weeks old were divided into age-matched sham and RT groups. A single 20-Gy fraction to the prostate was delivered to RT animals. Penile bulb, shaft, and testes were excluded from treatment fields.

MAIN OUTCOME MEASURES

Bioassay and intracavernous pressure (ICP) measurements were conducted at 2, 4, and 9 weeks following RT. Perfusion analysis of the corpora cavernosa (CC) was conducted using Hoechst injected prior to sacrifice. Penile shaft and cavernous nerve (CN) were evaluated by immunohistochemistry. Plasma testosterone level was analyzed using a testosterone enzyme-linked immunosorbent assay (ELISA) assay kit.

RESULTS

Irradiated animals demonstrated statistically significant time-dependent functional impairment of EF by bioassay and ICP measurement from 4 weeks. Neuronal nitric oxide synthase (NOS) expression was decreased in CN by 4 weeks. In CC, expression levels of anti-alpha smooth muscle actin and endothelial NOS were significantly decreased at 9 weeks. In penile dorsal vessels, smooth muscle/collagen ratio was significantly decreased at 4 and 9 weeks. Additionally, Hoechst perfusion showed time-dependent decrease in CC of RT animals, whereas CD31 expression was not affected. No toxicities were noted; testosterone levels were similar in both groups.

CONCLUSION

We demonstrated time-dependent ED following image-guided stereotactic RT. Our results imply that reduction of neuronal NOS expression in cavernous nerve could trigger consecutive reduction of smooth muscle content as well as blood perfusion in CC that resulted in corporal veno-occlusive dysfunction. Present study could be a cornerstone to future research that may bring comprehensive scientific understanding of radiation-induced ED.

Predictors of response to sildenafil citrate following radiation therapy for prostate cancer

INTRODUCTION

Phosphodiesterase type 5 inhibitor (PDE5) use is a treatment strategy for prostate cancer patients with post-radiation therapy (RT) erectile dysfunction (ED).

AIM

To define the predictors of sildenafil response in men treated with RT for prostate cancer.

MAIN OUTCOME MEASURES

International Index of Erectile Function (IIEF).

METHODS

Patients were enrolled prospectively if they met the following criteria: (i) either a three-dimensional conformal external beam (EBRT) or brachytherapy (BT) with or without androgen deprivation (AD) for prostate cancer; (ii) self-reported ability to have sexual intercourse prior to RT; (iii) experienced onset of ED following RT; (iv) candidates for sildenafil citrate use; (v) followed-up periodically; and (vi) completed the IIEF at least 12 months after RT. Failure to respond to sildenafil was defined as IIEF-erectile function (EF) domain score of <22.

RESULTS

One hundred fifty-two patients met all the criteria: 110 in the EBRT group and 42 in the BT group. Mean age was 62 years. The mean follow-up was 38 months. Mean radiation dose for EBRT was 78 Gy and for BT was 101 Gy. Thirty-five patients received AD, 25% of EBRT, and 62% of BT patients. Sixty-one percent of the patients receiving AD had exposure only pre-RT, whereas 39% had pre- and post-RT AD exposure. The mean duration of AD was 4.6 months. Post-RT IIEF-EF domain score at >24 months was 17. Successful response to sildenafil occurred in 68% of men at 12 months after RT, 50% at 24 months, and 36% at 36 months. On multivariable analysis, predictors of failure to respond to sildenafil were: older age, longer time after RT, AD > 4 months duration, and RT dose > 85 Gy. Modality of radiation delivery was not predictive of sildenafil failure.

CONCLUSIONS

A steady decrease in sildenafil response was seen with increasing duration after RT. Several factors were predictive of sildenafil failure.