Toward Prostate Cancer Contouring Guidelines on MRI: Dominant Lesion Gross and Clinical Target Volume Coverage via Accurate Histology Fusion

Abstract

volume is critical in treatment planning. Whether by expert guidelines, retrograde urethrography, bony landmark, ultrasound, or CT-based planning, there is discordant anatomic information regarding the distance between apex and the bulb, also known as the genitourinary diaphragm (GUD) or membranous urethra length (MUL). In this study, we use MRI with endorectal coil in a large series of patients to better characterize the MUL in radiation therapy planning. Materials/Methods: Patients with early stage, clinically localized prostate cancer (Gleason 6 and 7, cT1c-cT2b, PSA 85% interobserver agreement within 2 mm measurement. There was no association between MUL and patient age, T-stage, Gleason score, patient height, weight, or NCCN risk group. Conclusions: Although there remains variability, the median MUL, or GUD length, is 15 mm. This report likely represents the largest evaluation of the pre-treatment MUL in men with prostate cancer treated with external beam radiation. Our data challenges traditional guidelines between the apex and bulb from smaller series and adds to critical anatomic information of male urethral length and prostate apex anatomy. Prostate MRI with endorectal coil produces a reliable MUL and should be used to optimize target volume delineation at the prostate apex. Author Disclosure: N.K. Taunk: None. O. Akin: None. X. Pei: None. M. Zelefsky: None.