Identification of Key Anatomic Structures on Magnetic Resonance Imaging During Prostate Stereotactic Body Radiation Therapy for Dose Avoidance to Reduce Erectile Dysfunction Risk.

Abstract

Postradiation therapy erectile dysfunction can significantly impact the quality of life of patients with prostate cancer (PCa). Critical anatomic structures, such as the neurovascular bundles (NVBs), internal pudendal arteries (IPAs), penile bulb, and corporal tissues track near the prostate, making them susceptible to radiation-related damage. This study aimed to evaluate the anatomic patterns of these structures and their relationship with the prostate and to provide comprehensive illustrative examples on magnetic resonance imaging (MRI) scans. Consecutive patients with PCa who underwent MRI-linear accelerator-based stereotactic body radiation therapy from January 2024 until December 2024 were included. NVB patterns were classified into 3 categories: (1) "classical" with discrete NVB elements, (2) "adherent," dispersed and adherent to prostatic capsule, and (3) "absent." The smallest distance between the IPA and the prostate capsule and the membranous urethral length, serving as a surrogate for the distance between corporal tissue and prostatic apex, were also measured. These MRI scan findings were compared between prostate volumes >40 and <40 mL and between MRI scan findings and pathologic features of the dominant intraprostatic lesion. A total of 160 men (median age 70 years, interquartile range [IQR], 64-76) were included. The most common NVB pattern was "classic" (80.0%-85.0%), followed by the "adherent" NVB pattern (13.8%-18.1%). The median smallest distance between the IPA and prostate was 2.3 cm (IQR, 1.8-2.8 cm), with 3.1% to 3.8% <1.0 cm. The median membranous urethral length was 1.5 cm (IQR, 1.2-1.8 cm), with 2.5% of patients <1.0 cm. No significant association was found between these MRI scan features and prostate volume or other variables (P = .09-.99). In conclusion, most patients with PCa demonstrated favorable anatomy for potential dose sparing of critical structures. Comprehensive MRI scan illustrations are provided to help radiation oncologists recognize the location, trajectory, and relationship of these structures, facilitating their contouring and ultimately aiding in achieving meaningful dose reductions to these erectile function structures.