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Mixed performance of PIRADS v2: a validation study
James Walton1, Sajal Pokharel1, E. David Crawford2, Kavita Garg1, Kimberly E. Lind1, Emma Murugaverl3, and Nayana U. Patel1

1Radiology, University of Colorado School of Medicine, Aurora, CO, United States, 2Urology, University of Colorado School of Medicine, Aurora, CO, United States, 3Lake Erie College of Osteopathic Medicine

Synopsis

The second version of the Prostate Imaging Reporting and Data System (PIRADSv2) is the new standard for interpreting prostate MRI. Validation studies have been performed of this scheme, but many have used targeted biopsies as the reference standard. Our validation study is unique in utilizing 3D trans-perineal mapping biopsy (3DTMB) as the reference standard. With a total of 41 MRI lesions, PI-RADSv2 score = 5 lesions had a PPV for cancer of 1.0. However, when all significant lesions (PI-RADSv2 score ≥3) were included, the PPV is 0.29, with equal PPV of PI-RADS 3 and 4 lesions.


Purpose

The second version of the Prostate Imaging Reporting and Data System (PIRADSv2) has become the new standard for interpreting prostate MRI1. Several recent studies have been performed to validate this system2-7. These studies mainly used forms of targeted biopsies without2, 3 and with systematic biopsies4, 6 as the reference standard. Few have used whole mount prostatectomy results as the reference standard5, 7. However, none have used 3D trans-perineal mapping biopsy (3DTMB) as a reference standard. We undertook a study to validate PIRADS v2 by correlating pre-biopsy MRI followed by 3DTMB according to PIRADSv2 criteria for significant lesions (PIRADSv2 category ≥ to 3).


Methods

This was an institutional IRB-approved, HIPPA compliant retrospective single institutional cohort study. Patients who were suspected of having prostate cancer and who underwent prostate MRI between September 2010 and June 2013 followed by 3D trans-perineal mapping biopsy were included in the study. MRI was reviewed by two experienced abdominal radiologists independently, with any instances of discordance resolved by a third experienced abdominal radiologist. 3DTMB pathology was independently read by an experienced uropathologist. MRI data were co-registered to the 3DTMB data by dividing prostate gland into 12 segments in both sets of data. We evaluated the association between PIRADSv2 and 3DTMB outcomes using generalized estimating equations regression.


Results

There were a total of 41 MRI lesions called on final consensus in 41 patients. Lesions with PI-RADSv2 score = 5 were significantly associated with cancer and had a positive predictive value (PPV) of 1.0. PIRADSv2 score = 4 or 3 each had a PPV of 0.22, thus scores of 3 compared to 4 were not statistically different. Including all MRI lesions (PIRADSv2 score≥3), the PPV was 0.29.

Discussion

Lesions with a PIRADSv2 score = 5 had a high PPV for prostate cancer on 3DTMP. Interestingly, PIRADSv2 score = 4 lesions have a surprisingly low PPV, which was equal to the PPV for PIRADSv2 score = 3 lesions in our study. The score = 3 and score = 4 data are discrepant from many of the other recent validation studies. In these studies, the reported PPV for PIRADSv2 score ≥3 have been higher, approximately 0.8 4, 6. Other studies did not directly report PPV and used a cutoff of PIRADSv2 score ≥4 but also reported higher accuracy values2, 3, 5.

Conclusion

PIRADSv2 score = 5 lesions have a high positive predictive value for prostate cancer on 3DTMP.

Acknowledgements

No acknowledgement found.

References

1. Weinreb, J.C., et al., PI-RADS Prostate Imaging - Reporting and Data System: 2015, Version 2. Eur Urol, 2016. 69(1): p. 16-40.

2. Kasel-Seibert, M., et al., Assessment of PI-RADS v2 for the Detection of Prostate Cancer. Eur J Radiol, 2016. 85(4): p. 726-31.

3. Polanec, S., et al., Head-to-head comparison of PI-RADS v2 and PI-RADS v1. Eur J Radiol, 2016. 85(6): p. 1125-31.

4. Baldisserotto, M., et al., Validation of PI-RADS v.2 for prostate cancer diagnosis with MRI at 3T using an external phased-array coil. J Magn Reson Imaging, 2016. 44(5): p. 1354-1359.

5. Park, S.Y., et al., Prostate Cancer: PI-RADS Version 2 Helps Preoperatively Predict Clinically Significant Cancers. Radiology, 2016. 280(1): p. 108-16.

6. Zhao, C., et al., The efficiency of multiparametric magnetic resonance imaging (mpMRI) using PI-RADS Version 2 in the diagnosis of clinically significant prostate cancer. Clin Imaging, 2016. 40(5): p. 885-8.

7. Greer, M.D., et al., Accuracy and agreement of PIRADSv2 for prostate cancer mpMRI: A multireader study. J Magn Reson Imaging, 2016.


Figures

78 year old man with elevated PSA underwent prostate MRI. In the left posterolateral peripheral zone mid-gland to apex, there is a 2.1 cm lesion which is markedly hypointense on ADC map (A), markedly hyperintense on high b-value image (B), moderately hypointense on T2-weighted image (C), and shows early enhancement on dynamic contrast enhanced sequences (D). This was a PIRADSv2 score 5 lesion that corresponded to multiple adjacent 3D mapping biopsy cores that were positive for adenocarcinoma.

3D representation of the transperineal mapping biopsy results in craniocaudal (A) and anterioposterior (B) projections of the patient in the above MRI figure. The colored diamonds correspond to biopsy cores that were positive for cancer on histology. Green diamonds represent Gleason 4+3 = 7, orange diamond was Gleason 3+4=7, and blue diamond was Gleason 6. Given that all the positive cores were adjacent to one another, all positive cores were taken to be from one lesion. The location of the tumor in the left posterior mid-gland to apex corresponds to the lesion seen on MRI in the prior figure.

Proc. Intl. Soc. Mag. Reson. Med. 25 (2017)
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