Evaluating Factors Associated with Radiation-induced Erectile Dysfunction After Stereotactic Radiotherapy

Objective: Erectile dysfunction (ED) is a common side effect of prostate cancer radiotherapy (RT). Stereotactic body RT (SBRT) is a highly conformal RT technique that utilizes ultra-hypofractionated RT with 4-5 fractions, but the effect of SBRT on sexual function remains uncertain. This study aimed to analyze the possible relationship between SBRT and ED in patients with clinically localized prostate cancer. Methods: Between January 2013 and December 2019, the factors affecting ED were analyzed in 55 patients with preserved potency following SBRT +/− hormone therapy for lowto intermediate-risk prostate cancer. While planning RT, the penile bulb was delineated as an organ at risk (OAR) in the computed tomography scan. A total dose of 35-36.25 Gy was administered in five fractions of 7-7.25 Gy through alternating-day SBRT treatment with CyberKnife. Erectile function was assessed using the International Index of Erectile Function (IIEF-5) scale at baseline and 3 months, 1 year, and 2 years after SBRT. Groups were formed with respect to post-treatment potency, as measured by IIEF-5. Results: The median patient age was 68.5 years, and the median follow-up duration was 58 months. After SBRT, 56.4% of the patients had preserved potency. Age and inclusion of the proximal seminal vesicles in the planning target volume (PTV) were significantly different between the potency groups in the univariate analysis (p=0.028 and p=0.036). In the multivariable analysis, the PTV and inclusion of the proximal third of the seminal vesicles in the PTV were significant in the development of ED (p=0.038 and p=0.020). Conclusion: Although modern RT techniques are used in prostate cancer treatment, erectile function may be affected. Considering the complex mechanisms of ED, it would be erroneous to explain the decline in potency based only on dosimetric factors related to OAR doses.