The purpose of this study was to investigate the utility of pre-treatment multiparametric magnetic resonance imaging (mpMRI) in a modern cohort of intermediate and high-risk prostate cancer patients treated with primary radiotherapy.

One hundred twenty three men with National Comprehensive Cancer Network (NCCN) intermediate or high-risk prostate cancer were treated with primary EBRT and/or brachytherapy and had evaluable pre-treatment mpMRI with endorectal coil. Images were assessed for the presence of radiographic extraprostatic extension (rEPE), seminal vesicle invasion (rSVI), lymph node involvement (LNI), sextant involvement, and largest axial tumor diameter. Imaging characteristics were analyzed along with clinical risk factors against freedom from biochemical failure (FFBF). Median follow-up time was 50 months.

Fourteen (11%) men developed biochemical failure. The 5-year FFBF was 94% in intermediate-risk patients and 82% in high-risk patients (p < 0.01). mpMRI findings including rEPE (29% vs. 66%, p < 0.01), rSVI (6% vs. 25%, p < 0.01), LNI (1% vs. 30%, p < 0.01), and largest axial tumor size> 15 mm (27% vs. 48%, p = 0.02) were identified in men with intermediate vs. high risk prostate cancer, respectively. mpMRI features associated with 5-y FFBF biochemical failure on univariate analysis included rEPE (80% vs 98%), rSVI (55% vs. 96%), LNI (65% vs. 93%), and largest axial tumor size >15mm (81% vs. 94%, all p < 0.01). Men without any high risk MRI finding had a 5-y FFBF of 100% vs. 81% (p < 0.01). Adverse imaging features (HR 8.9, p < 0.01) were independently associated with biochemical failure in a bivariate model analyzed alongside clinical risk category (HR 3.2, p = 0.04).

Pre-treatment mpMRI findings are strongly associated with biochemical outcomes in a modern cohort of intermediate and high-risk patients treated with primary radiotherapy. mpMRI may aid risk stratification beyond clinical risk factors in men treated with radiation therapy; further study is warranted to better understand how mpMRI can be used to individualize therapy.