Interreader agreement of PI-RADS v. 2 in assessing prostate cancer with multiparametric MRI: A study using whole-mount histology as the standard of reference

Background: Most studies assessing interreader agreement of Prostate Imaging Reporting and Data System v. 2 (PI-RADS v2) have used biopsy as the standard of reference, thus carrying the risk of not definitively noting all existent cancers. Purpose: To evaluate the interreader agreement in assessing prostate cancer (PCa) of PI-RADS v2, using whole-mount histology as the standard of reference. Study Type Monocentric prospective cohort study. Population: In all, 48 patients with biopsy-proven PCa referred for radical prostatectomy, undergoing staging multiparametric magnetic resonance imaging (mpMRI) between May 2016 to February 2017. Field Strength/Sequence: 3.0T system using high-resolution T-2-weighted imaging, diffusion-weighted imaging (echo-planar imaging with maximum b-value 2000 sec/mm(2)), and dynamic contrast-enhanced imaging (T-1-weighted high resolution isotropic volume examination; THRIVE) Assessment: Three radiologists blinded to final histology (2-8 years of experience) analyzed mpMRI images independently, scoring imaging findings in accordance with PI-RADS v2. On a per-lesion basis, we calculated overall and pairwise interreader agreement in assigning PI-RADS categories, as well as assessing malignancy with categories >= 3 or >= 4, and stage >= pT3. Statistical Tests: Cohen's kappa analysis of agreement. Results: On 71 lesions found on histology, there was moderate agreement in assigning PI-RADS categories to all cancers (k = 0.53) and clinically significant cancers (csPCa) (k = 0.47). Assessing csPCa with PI-RADS >= 4 cutoff provided higher agreement than PI-RADS >= 3 cutoff (k = 0.63 vs. 0.57). Interreader agreement was higher between more experienced readers, with the most experienced one achieving the highest cancer detection rate (0.73 for csPCa using category >= 4). There was substantial agreement in assessing stage >= pT3 (k = 0.72). Data Conclusion: We found moderate to substantial agreement in assigning the PI-RADS v2 categories and assessing the spectrum of cancers found on whole-mount histology, with category 4 as the most reproducible cutoff for csPCa. Readers' experience influenced interreader agreement and cancer detection rate.