Prostate cancer patients have a number of excellent treatment options to consider, and quality of life following treatment is often a consideration in treatment choice. One critical quality of life concern for patients diagnosed with prostate cancer is sexual function. Previous studies point to a vascular mechanism of impotence post-radiation therapy, as opposed to a nerve-based mechanism following surgery. In this study, the critical vascular structures (internal pudendal artery and corpus cavernosum) are defined by MRI-based imaging and included in treatment planning for radiation treatments, hopefully preserving critical artery function. This study will collect erectile function preservation rates at 5-years post-vessel-sparing radiotherapy with or without aids using the patient reported using the simplified three-question erectile function scale.