Initial prospective evaluation of the prostate imaging reporting and data standard (PI-RADS): Can it reduce unnecessary MR guided biopsies?

Purpose: To evaluate the performance of the prostate imaging reporting and data standard (PI-RADS) and the effect of reader experience. Materials and Methods: A consecutive patient cohort of 254 patients who underwent both a detection MRI between January 1st, 2012 and December 31st, 2012 and a subsequent MR guided biopsy were included in this study. All patients were prospectively reported by one radiologist according to the PI-RADS guidelines. In total 10 different radiologists reported patients in this cohort. Of these 10 radiologists, 2 radiologist can be considered experts (19 and 12 years of experience with prostate MRI) and 8 can be considered inexperienced (3 years or less experience with prostate MRI). Together, the 2 experienced readers reported 108 patients and 146 were reported by the 8 inexperienced readers The radiologists reported 436 lesions in these patients of which 339 were biopsied. Of these 339 biopsied lesions 190 were prostate cancer. Of these 190 prostate cancer 127 lesions had a Gleason 4 or higher component and were considered high-grade prostate cancer, all others were considered low grade. The distribution of non-cancers, low-grade cancers and high-grade cancer was similar between the inexperienced and experienced observers (44%/19%/36% vs. 46%/16%/38%). Each lesion received, according to the PI-RADS guidelines, a score between 1 and 5. The sensitivity, specificity, positive predictive value and negative predictive value were calculated at each of the PI-RADS scores relative to the biopsy results. High-grade cancers with a PI-RADS score above or equal to the threshold are true positives. Non-cancers below the threshold were considered true negatives. This was done for both the inexperienced and experienced radiologists. Results: In total 19 PI-RADS 2, 67 PI-RADS 3, 112 PI-RADS 4 and 141 PI-RADS 5 lesions were biopsied. No PI-RADS 1 lesions were biopsied. The inexperienced reader sensitivities for PIRADS 2, 3, 4 and 5 are: 1, 1, 0.96 and 0.69 respectively. The experienced readers obtained 1, 1, 0.98 and 0.71. The corresponding specificities were 0, 0.16, 0.48 and 0.71 for the inexperienced and 0, 0.07, 0.36 and 0.76 for the experienced readers. The positive and negative predictive values were 0.46, 0.50, 0.61, 0.71 and 1, 1, 0.93, 0.74 for the inexperienced readers. For the experienced readers we obtained 0.46, 0.48, 0.57, 0.84 and 1, 1, 0.96, 0.78 respectively. Conclusion: In this population we can see that especially PI-RADS 4 and 5 classifications have excellent sensitivity, specificity, PPV and NPV characteristics. From this data we conclude that only PI-RADS 4 and 5 lesions require biopsy; inexperienced and experienced readers have sensitivities of 0.96 and 0.98 at this threshold. Experience matters: the number of unnecessary biopsies in PI-RADS 5 lesions reduces from 29/100 to 16/100 between experienced and inexperienced readers. Clinical relevance: PI-RADS reported lesions may help reduce the number of unnecessary biopsies. The strong effect of experience emphasizes the need for adequately trained radiologists for reporting prostate MR.