Endorectal MRI for risk classification of localized prostate cancer: Radiographic findings and influence on treatment decisions

- When used in the initial evaluation of localized prostate cancer, endorectal MRI demonstrates high-risk imaging features such as extracapsular extension, seminal vesical invasion, and lymph node involvement at an incidence related to clinical risk category (P< 0.05).
- Imaging results had clinical use in a radiation oncology setting, resulting in a change in management for 18% of men, most commonly as a result of improved appreciation of the extent of disease within the prostate and seminal vesicles.
- Given the potential for results to influence management, this study substantiates the notion that endorectal MRI is useful in the initial evaluation of men who are candidates for active surveillance, brachytherapy, or external beam radiation therapy.

PurposeTo report the results of endorectal coil magnetic resonance imaging (eMRI) in patients with localized prostate cancer, and how these images influenced radiotherapeutic management.Materials and methodsA total of 122 men with localized adenocarcinoma of the prostate referred to radiation oncology underwent 3-T eMRI between 2010 and 2014, to evaluate candidacy for active surveillance (n = 26) and brachytherapy as monotherapy (n = 47), or to further risk stratify intermediate-risk (n = 29) or high-risk (n = 20) men before external beam radiation therapy. By National Comprehensive Cancer Network classification, men had low-risk (28%), intermediate-risk (55%), or high-risk (17%) disease. Multiparametric MRI sequences included T2-weighted, diffusion-weighted imaging, and dynamic contrast-enhanced imaging. Radiographic extracapsular extension, seminal vesicle invasion (rSVI), and pelvic lymph node involvement (LNI) were graded as negative, indeterminate, or positive. A dominant nodule was defined as a nodule≥1.5 cm. Changes in management were identified comparing pre-MRI and post-MRI plan of care.ResultsThe rates of radiographic extracapsular extension, radiographic seminal vesicle invasion, lymph node involvement, and dominant nodule were 39%, 7%, 12%, and 28%, respectively. The eMRI identified measurable disease in most patients with an increasing burden of disease (sextants involved, median nodule size) according to risk category (P<0.01). Changes in management after eMRI occurred in 18%, including 9%, 18%, and 33% of men with low-risk, intermediate-risk, or high-risk disease (P = 0.08), and 12%, 17%, and 22% of men who were candidates for active surveillance, brachytherapy as monotherapy, or external beam radiation therapy (P = 0.48), respectively.ConclusionThe eMRI influenced management in a risk-dependent fashion. Further study is required to determine the clinical importance of eMRI findings and to determine whether changes in management can lead to improved clinical outcome.