Comparison of prostate volume measured by transrectal ultrasound and magnetic resonance imaging: is transrectal ultrasound suitable to determine which patients should undergo active surveillance?

OBJECTIVES

To compare prostate volume obtained by transrectal ultrasound (TRUS) and endorectal MRI (eMRI) to assess the reliability of TRUS in determining prostate-specific antigen (PSA) density.

MATERIALS AND METHODS

Data for 2,410 patients diagnosed with localized prostate cancer (CaP) and treated with radical retropubic prostatectomy (RRP) at the University of Pennsylvania Health System between 1991 and 2005 was reviewed. Of these patients, 756 had both a preoperative TRUS and eMRI of the prostate performed. Prostate size was estimated using the prolate ellipsoid formula (height × width × length × π/6); maximal height or antero-posterior (A-P) diameter was determined using a midsagittal view for TRUS and an axial view for eMRI. Pearson's correlation, linear regression, and paired t-test were performed to compare prostate volumes estimated via both imaging modalities.

RESULTS

Average prostate size measured with TRUS and eMRI correlated significantly with one another (R = 0.801; P < 0.0001), demonstrating a strong linear relationship (y = 0.891x + 2.622, R(2) = 0.642). Comparison of PSA density also demonstrated a strong linear relationship (y = 0.811x + 0.053, R(2) = 0.765). Average prostate volume differed by 1.7 ml (TRUS relative to eMRI), which was statistically significant based on a paired t-test (P < 0.001). Upon stratification of patients into three groups based on average TRUS volume (≤ 30, >30-60, and >60 ml), significant correlation (0.318, 0.564, 0.650) and difference between volumes (-2.1, 4.0, 5.1 ml; P < 0.0001, P < 0.0001, P < 0.05 TRUS relative to eMRI) was maintained.

CONCLUSIONS

Prostate volume estimations with TRUS and eMRI are highly correlated. It is therefore, reasonable to conclude that in the hands of an experienced sonographer, TRUS is not only an efficient and economical examination, but also an accurate and reproducible modality to estimate prostate size.