Prostate Volumetric Assessment by Magnetic Resonance Imaging and Transrectal Ultrasound: Impact of Variation in Calculated Prostate-Specific Antigen Density on Patient Eligibility for Active Surveillance Program

Objective: The objective of this study was to investigate impact of prostate volume variations on prostate-specific antigen density (PSAD) and patient eligibility for active surveillance (AS). Methods: Prostate volume and PSAD were calculated for 46 patients with prostate cancer in AS who underwent prostate magnetic resonance imaging and transrectal ultrasound (TRUS). Manual method and 2 semi-automated methods for prostate segmentation (3D-SLICER and OsiriX) were used for MR volumetry. Results: Magnetic resonance volumetric methods showed very good agreement (intraclass correlation coefficient, 0.98). The concordance correlation coefficient was higher among MR volumetry methods (0.971-0.998) than between TRUS and MR volumetry (0.849-0.863). The variation in PSAD estimated by TRUS versus magnetic resonance imaging was higher in large prostates (r = 0.327, P = 0.027). Transrectal ultrasonography volumetry may improperly classify 20% of patients as eligible for AS with PSAD greater than 0.15 threshold. Conclusions: Although clinically used TRUS reliably estimates PSAD, it may misclassify some patients who are not eligible for AS based on PSAD criteria. Magnetic resonance-based volumetry should be considered for a more reliable PSAD calculation.