• Rossano Girometti, Gianluca Giannarini, Franco Greco, Miriam Isola, Lorenzo Cereser, Giuseppe Como, Stefano Sioletic, Stefano Pizzolitto, Alessandro Crestani, Vincenzo Ficarra, and Chiara Zuiani.
• Institute of Diagnostic Radiology, Department of Medicine, Udine, UD, Italy.
• J Magn Reson Imaging. 2019 Feb 1; 49 (2): 546-555.

BackgroundMost 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.PurposeTo evaluate the interreader agreement in assessing prostate cancer (PCa) of PI-RADS v2, using whole-mount histology as the standard of reference.Study TypeMonocentric prospective cohort study.PopulationIn 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/Sequence3.0T system using high-resolution T2 -weighted imaging, diffusion-weighted imaging (echo-planar imaging with maximum b-value 2000 sec/mm2 ), and dynamic contrast-enhanced imaging (T1 -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 TestsCohen's kappa analysis of agreement.ResultsOn 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 ConclusionWe 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.Level Of Evidence2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:546-555.© 2018 International Society for Magnetic Resonance in Medicine.

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