Interobserver Agreement and Positivity of PI-RADS Version 2 Among Radiologists with Different Levels of Experience

Rationale and Objectives: To evaluate interobserver agreement of Prostate Imaging Reporting and Data System (PI-RADS) v2 category among radiologists with different levels of experience. The secondary objective was to evaluate the positivity for significant cancer among each category (splitting category 4 into two) and among different lesion sizes. Materials and Methods: Institutional review board and ethics comitee approved retrospective study. Eight radiologists with different levels of experienced in prostatic magnetic resonance imaging—two more experienced, four with intermediate experience, and two abdominal radiology fellows—interpreted 160 lesions. Reference standard was fusion-targeted biopsy. Percentage agreement, k coefficients, and analysis concordance were used. Results: Coefficient of concordance according to categories was 0.71 considering both zones, 0.72 for peripheral zone (PZ) and 0.44 for peripheral zone (TZ). Agreement for PI-RADS score of 3 or greater was 0.48 in PZ and 0.57 in TZ. Tumor positivity rates were 54.3% and 66.0% for PI-RADS 3 + 1 and 4 for PZ, respectively; and 25.0 and 49.2% for PI-RADS 3 + 1 and 4 for TZ, respectively (p < 0.001 in both analysis). Lesions <10, 10–14, and ≥15 mm had 55.3%, 74.6%, and 93.5% of positivity rates for cancer in PZ (p = 0.002 and <0.001) and 26.7%, 56.5%, and 59.6% in TZ, respectively (p = 0.245 and 0.632). Sensitivities, specificities, and accuracies of magnetic resonance imaging for prostate cancer using PI-RADS v2 were 76%, 72%, and 74% for PZ; and 76%, 69%, and 71% for TZ, respectively. Conclusion: This study shows that PI-RADS v2 has overall good interobserver agreement among radiologists with different levels of experience. PI-RADS category 3 + 1 showed lower positivity rates for significant cancer compared to category 4. Lastly, lesions 10–14 mm has similar positivity rates compared to ≥15 mm for TZ lesions.