High false-positive rates of prostate cancer diagnosis techniques have resulted in unnecessary biopsies and increased costs of care. This study compared the prostate cancer diagnosis by multiparametric MRI and MRI-ultrasound fusion guided biopsy at our institution, with the ultimate goal of improving MRI diagnosis of prostate cancer. At our institution, multiparametric MRI PI-RADS scores and MRI-ultrasound fusion guided biopsy Gleason scores agreed 46-57% of the time which falls within the ranges in literature.
Introduction
Multiparametric MRI diagnosis of prostate cancer (PCa) is a promising technique but its high false-positive rate of prostate cancer diagnosis has resulted in unnecessary prostate biopsies and increased costs of care.1 Prostate Imaging-Reporting and Data System (PI-RADS) is used by radiologists to score the significance of disease usually based on diffusion-weighted MRI, T2 MRI, and contrast-enhanced MRI. Urologists then perform targeted biopsies guided by MRI-ultrasound fusion along with standard 12-core biopsies. However, there are often inconsistencies between PI-RADS scores and targeted biopsy Gleason scores (GS) caused by various factors. It remains unclear if targeted biopsy guided by MRI-ultrasound fusion objectively improves PCa detection rates versus non-targeted standard core biopsy.2
The goal of this study was to compare the diagnosis by MRI and MRI-ultrasound fusion-guided biopsy at our institution, with the ultimate goal of improving MRI diagnosis of prostate cancer.
Methods
A retrospective cross-sectional study was done on standard non-targeted 12-core biopsies and 192 targeted prostate peripheral zone biopsies in 151 patients from January 2014 to June 2017. Patients’ ages at exam ranged from 53-77 years and prostate volumes ranged from 20-165 cc. Each lesion identified was treated as a separate entity for the analysis. Radiologist PI-RADS scores of 4 and 5 (range: 1-5) from standard diffusion-weighted MRI, T2 MRI, and contrast-enhanced MRI were considered significant PCa. PI-RADS scores were compared to pathologist GS of standard 12-core biopsies and target biopsies guided by MRI-ultrasound fusion. Tabulations were done for GS ≥7 (≥3+4 or ≥4+3) considered as significant PCa.Results
Prostate lesions with PI-RADS scores ≤3 agreed well with no cancer in both targeted and standard 12-core biopsies. With GS ≥7 considered as significant PCa, the agreement of PI-RADS score 4 and 5 lesions with significant PCa GS in target biopsies was 47% (16/34) and 38% (3/8) respectively. With the addition of standard 12-core biopsy data, the accuracy was unaffected for PI-RADS score 4 lesions (46%, 26/57) but improved for PI-RADS score 5 lesions (57%, 16/28). For the 16 PI-RADS score 5 targeted MRI-ultrasound guided biopsies, the target biopsy GS would match the standard core biopsy GS of the same region 75% (12/16) of the time.Discussion
PI-RADS scores and MRI-ultrasound fusion guided biopsy GS agreed 46-57%
of the time for PI-RADS score 4 and 5 lesions at our institution. These values
fall within the established 50-83% range of positive predictive values (PPVs) of
MRI for diagnosis of PCa.1
There are substantial inconsistencies between PI-RADS scores and biopsy GS. Factors contributing to the inconsistencies includes MRI image distortion, incomplete standardization of prostate MRI radiology reads, misregistration between prostate MRI and transrectal ultrasound, misregistration due to prostate distortion from ultrasound probe pressure during biopsy, and biopsy sampling errors to name a few. Currently, coupling of targeted and non-targeted biopsies and increasing biopsy cores have been proven to improve accuracies of PCa diagnoses.3,4 A similar prospective randomized control trial comparing transrectal ultrasound guided biopsies to standard core biopsies failed to show significant improvement.5
Conclusion
Multiparametric MRI PI-RADS scores of 4 and 5 agreed with significant PCa GS of targeted biopsy guided by MRI-ultrasound fusion 46-57% of the time at our institution comparable to established PPV values in literature. We subsequently identified some limitations of this PCa detection process. Two major issues result from the limitations of this technique. The low accuracy of multiparametric MRI interpretations results in unnecessary prostate biopsies, while unreliability of MRI-ultrasound fusion guided biopsy detection of PCa contributes to the underdiagnosis and undertreatment of PCa.6,7 Based on the results of this study, we plan to focus on improving in the consistency of multiparametric MRI interpretation and the synchronization of MRI and ultrasound images.1. Hamoen EHJ, de Rooij M, Witjes JA, Barentsz JO, Rovers MM. Use of the Prostate Imaging Reporting and Data System (PI-RADS) for Prostate Cancer Detection with Multiparametric Magnetic Resonance Imaging: A Diagnostic Meta-analysis. Eur Urol. 2015;67(6):1112-1121.
2. Siddiqui MM, Rais-Bahrami S, Truong H, et al. Magnetic resonance imaging/ultrasound-fusion biopsy significantly upgrades prostate cancer versus systematic 12-core transrectal ultrasound biopsy. Eur Urol. 2013;64(5):713-719.
3. Taylor JA, 3rd, Gancarczyk KJ, Fant GV, McLeod DG. Increasing the number of core samples taken at prostate needle biopsy enhances the detection of clinically significant prostate cancer. Urology. 2002;60(5):841-845.
4. Kuligowska E, Barish MA, Fenlon HM, Blake M. Predictors of prostate carcinoma: accuracy of gray-scale and color Doppler US and serum markers. Radiology. 2001;220(3):757-764.
5. Arsov C, Rabenalt R, Blondin D, et al. Prospective randomized trial comparing magnetic resonance imaging (MRI)-guided in-bore biopsy to MRI-ultrasound fusion and transrectal ultrasound-guided prostate biopsy in patients with prior negative biopsies. Eur Urol. 2015;68(4):713-720.
6. Schroder FH, Hugosson J, Roobol MJ, et al. Screening and prostate-cancer mortality in a randomized European study. N Engl J Med. 2009;360(13):1320-1328.
7. Djavan B, Ravery V, Zlotta A, et al. Prospective evaluation of prostate cancer detected on biopsies 1, 2, 3 and 4: when should we stop? J Urol. 2001;166(5):1679-1683.