Comparison of Prostate Volume Measured by Endorectal Coil MRI to Prostate Specimen Volume and Mass After Radical Prostatectomy

Abstract

To compare prostate volume measurements from 3-Tesla endorectal coil magnetic resonance imaging (ERC MRI) obtained with the prolate ellipsoid volume formula (EVF) and volumetry to pathology-based volume measurements. The institutional review board waived informed consent for this retrospective, health insurance portability and accountability act (HIPAA) compliant study, which included 195 patients who underwent 3-T ERC MRI between January 2008 and October 2011 and had pathologic prostate measurements available. Two readers in consensus measured the prostate length, height, and width on each MRI. They estimated prostate volumes using the prolate EVF (length × height × width × [π/6]) and also by performing three-dimensional volumetry. Pathologic specimen mass and dimensions were used to calculate prostate volume. Agreement was measured with Lin's concordance correlation coefficient (CCC). Volume differences were assessed using the Wilcoxon signed-rank test. Correct prostate-specific antigen (PSA) density classification rates were compared between EVF-based and volumetry-based PSA density levels using the exact McNemar test, with pathology-based PSA density as the reference standard. Concordance was high between EVF and volumetry measurements (CCC, 0.950 [95% confidence interval, 0.935-0.962]) and between both kinds of MRI measurements and pathology (both CCC > 0.80). Based on a cut-off of ≤0.15 ng/mL/cm(3), use of EVF-based volume produced correct classification of 46 of 48 PSA density levels >15 ng/mL/cm(3) and 113 of 147 PSA density levels ≤15 ng/mL/cm(3); use of volumetry-based volume produced correct classification of 47 of 48 PSA density levels >15 ng/mL/cm(3) and 121 of 147 PSA density levels ≤15 ng/mL/cm(3). Rates of underclassification (P > .95) and overclassification (P = .10) did not differ significantly between EVF and volumetry. EVF appears to be suitable for measuring prostate volume from ERC-MRI.