Restriction Spectrum Imaging as a quantitative biomarker for prostate cancer with reliable positive predictive value.

Abstract

Purpose: Positive predictive value of PI-RADS for clinically significant prostate cancer (csPCa, grade group [GG]≥2) varies widely between radiologists. The Restriction Spectrum Imaging restriction score (RSIrs) is a biophysics-based metric derived from diffusion MRI that could be an objectively interpretable biomarker for csPCa. We aimed to evaluate performance of RSIrs for patient-level detection of csPCa in a large and heterogenous dataset, and to combine RSIrs with clinical and imaging parameters for csPCa detection.

Materials and methods: At 7 centers, participants underwent prostate MRI between January of 2016 and March of 2024. We calculated patient-level csPCa probability based on maximum RSIrs in the prostate and compared patient-level csPCa detection to apparent diffusion coefficient (ADC) and PI-RADS using area under the ROC curve (AUC). We also evaluated csPCa discrimination by grade group and combining RSIrs with clinical risk factors via multivariable regression.

Results and conclusions: Among patients that met the inclusion criteria (n=1892), probability of csPCa increased with higher RSIrs. Among biopsy-naïve patients (n=877), AUCs for GG≥2 vs. non-csPCa were: RSIrs=0.73 (0.69-0.76), ADC=0.54 (0.50-0.57), and PI-RADS=0.75 (0.71-0.78). RSIrs significantly outperformed ADC (p<0.01) and was comparable to PI-RADS (p=0.31). RSIrs and PI-RADS combined outperformed either alone. The model with RSIrs, PI-RADS, age, and PSA density achieved the best discrimination of csPCa. RSIrs is an accurate and reliable quantitative biomarker that performs better than conventional ADC and comparably to expert-defined PI-RADS for patient-level detection of csPCa. RSIrs provides objective estimates of probability of csPCa that do not require radiology expertise.