Rationale and Objectives
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.
Methods
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.
Results
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.
Conclusions
EVF appears to be suitable for measuring prostate volume from ERC-MRI.
The accurate measurement of in vivo prostate volume is important for a wide variety of clinical situations. For patients with benign prostatic hypertrophy (BPH), prostate volume measurements are used to monitor the condition and assess the efficacy of treatment . For patients with prostate cancer, prostate volume measurements have prognostic significance and may influence diagnosis and management. A number of recent studies have shown that prostate volume can be useful in models for predicting the presence of indolent or clinically “insignificant” tumors . Furthermore, accurate estimation of prostate volume is necessary to calculate the prostate-specific antigen (PSA) density (the PSA level divided by the prostate volume), which may be used to help distinguish BPH from prostate cancer and to predict adverse treatment outcomes . Ha et al. recently reported that among patients with low-risk prostate cancer (defined as a biopsy-derived Gleason score ≤6 in a single positive core, clinical stage ≤T1c, PSA ≤10 ng/mL, and unremarkable magnetic resonance imaging [MRI] results) who underwent radical prostatectomy, PSA density was a predictor of advanced disease (the reported cutoff was a PSA density of 0.085 ng/mL/cm 3 ). Although a range of PSA density cutoffs have been reported in the literature, Epstein et al. found that a PSA density of 0.1–0.15 ng/mL/cm 3 , along with low- to intermediate-grade cancer <3 mm found in only one needle biopsy core specimen, constituted the best model to predict preoperatively insignificant tumor.
Prostate volume measurements are also used to determine patient selection for brachytherapy and the number of radioactive seeds used for the procedure . For patients with larger prostates, brachytherapy is associated with a higher incidence of side effects and is typically not recommended owing to technical difficulties primarily related to the encroachment of the pubic arch over the prostate gland .
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Materials and methods
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MRI Data Acquisition
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Pathology Preparation
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Analysis
MR Measurements
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Pathology Measurements
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Statistical Analysis
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Results
Patient Characteristics
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MRI and Pathology Volume Analyses
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Table 1
Volume Measurements
Volumes (cm 3 ) Median (IQR) MRI volumetry 41.6 (30.42–60.21) MRI EVF 41.5 (29.08–55.04) Pathology SGF 51.6 (41.14–66.86)
EVF, ellipsoid volume formula; IQR, interquartile range; MRI, magnetic resonance imaging; SGF, specific gravity formula.
Table 2
Differences between Volume Measurements
Volume Differences (cm 3 ) Median (IQR)P Value MRI EVF − MRI volumetry 2.17 (−1.64 to 6.24) <.0001 Path SGF − MRI EVF 10.2 (−4.10 to 15.56) <.0001 Path SGF − MRI volumetry 7.74 (−3.25 to 13.28) <.0001
EVF, ellipsoid volume formula; IQR, interquartile range; MRI, magnetic resonance imaging; SGF, specific gravity formula.
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![Figure 4, Bland–Altman plots show comparisons between (a) prostate magnetic resonance (MR) volumes measured using ellipsoid volume formula (EVF) and prostate MR volume using volumetry, (b) specimen prostate volume measured using EVF and specimen prostate volume measured using specimen mass (specific gravity formula [SGF]), (c) prostate MR volume measured using EVF and prostate specimen volume measured using SGF.](https://storage.googleapis.com/dl.dentistrykey.com/clinical/ComparisonofProstateVolumeMeasuredbyEndorectalCoilMRItoProstateSpecimenVolumeandMassAfterRadicalProstatectomy/3_1s20S107663321500015X.jpg)
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MRI and Pathology PSA Density Analyses
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Discussion
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Acknowledgments
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