A comparison of prostate volumes measured using transrectal ultrasound and magnetic resonance imaging; and the effect of their differences on PSA density

Abstract

Aim: The aim of this study is to compare prostate volumes and calculated PSA densities measured by transrectal ultrasound performed by urologists with different levels of experience, and prostate volumes calculated based on magnetic resonance measurements. Methods: The study comprises patients who underwent transrectal needle biopsy between February 2015 and November 2018.

All of these patients underwent a multiparametric prostate MR using 1,5T Signa HDXT GE with endorectal coil beforehand. The ultrasound measurement, done using the Toshiba Applio 500 device with end-fire endorectal probe, was performed by three urologists with two, seven and 20 years of clinical experience.

Prostate volume was in all patients calculated by using the largest diameters in three perpendicular axes in the "width x height x length x 0.523" formula. PSA density was then calculated as total PSA/prostate volume in millilitres.

Results: A total of 582 were evaluated. The mean age was 62.86 years (31-91), average PSA was 8.70 ng/ml (0.53-75.00).

The mean difference between TRUS and MR measurement was +8.41 ml. The difference was +3.66 ml for the examiner with twenty years of experience, +11.19 ml for the examiner with seven years of experience and +8.12 ml for the examiner with two years of experience.

The average difference in PSA density between TRUS and MR was -0.025 ng/ml/ml. Using the PSA density cut-off value of 0.15 ng/ml/ml and 0.20 ng/ml/ml to indicate prostate biopsy, 8 % or 6 % less patients would have undergone prostate biopsy when using TRUS than with MR respectively.

Conclusion: In this cohort, transrectal ultrasonography yielded larger prostate volume estimates than magnetic resonance imaging; subsequently 6 % or 8 % less biopsies would have been performed when using PSA density as the only criterion for prostate biopsy.