Neurovascular Bundle-Sparing Radiotherapy for Prostate Cancer using MRI CT Registration: A Dosimetric Feasibility Study; Beyond the Abstract

One of the most significant toxicities with any definitive therapy for prostate cancer is erectile dysfunction. The risk of developing erectile dysfunction is multifactorial and includes both patient, tumor, and treatment related factors. As cure rates rise with prostate cancer, especially in low and intermediate risk populations, there is an emphasis to mitigate sexual dysfunction for improved patient quality of life.

As the technology for external beam radiation has quickly evolved from multi-field forward planning technique to inversely planned intensity modulated radiotherapy, the ability to spare normal tissue targets has improved. Previous studies have investigated limiting radiation dose to the crura and penile bulb with promising results. However there has been minimal literature looking at radiation dose to the neurovascular bundles owing to its difficult localization on CT imaging and proximity to the prostate gland. Given this lack of literature we wanted to assess the feasibility of contouring the neurovascular bundle on MRI and generating radiation plans that limited the dose to this structure. In our current study, we used pelvic simulation CT scan and pelvic MRI registration to accurately delineate and contour the neurovascular bundles. Using this technique with volumetric modulated arc therapy we showed dosimetrically that the neurovascular bundles could receive limited radiation without increasing the dose delivered to the rectum, bladder, and femoral heads. Additionally, there remained adequate coverage of the prostate gland itself. Taken together, it appears to be dosimetrically viable to spare the neurovascular bundle in external beam radiation planning.

Our study was limited by its lack of clinical outcomes and thus it is unclear if sparing the neurovascular bundle from radiation will improve erectile dysfunction. However, given the promising dosimetric results, our institution is validating the reproducibility of contouring the neurovascular bundle as well as designing prospective studies to assess the clinical impact of this treatment technique. 

Written by: Richard J. Cassidy, MD and Ashesh B. Jani, MD

Department of Radiation Oncology, Winship Cancer Institute of Emory UniversityAtlanta, GA

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