Prostate weight is the preferred measure of prostate size in radical prostatectomy cohorts

To evaluate the accuracy of calculated prostate volume variables in a radical prostatectomy (RP) cohort, as many recent studies use these measures of prostate size instead of prostate weight. To determine whether this accuracy could be improved by modifying the mathematical model used in the volume estimation.

Patients who underwent RP for prostate cancer at our associated institutions had calculated specimen volumes and weights from RP specimens determined at one pathology institution and transrectal ultrasonography (TRUS) volumes were recorded preoperatively (n= 236). Correlation analysis was performed and errors were determined for calculated volume variables when compared with prostate weight. Bland-Altman plots were drawn and concordance coefficients calculated. Analysis was repeated with smaller prostates mathematically modelled as bullet-shaped rather than ellipsoid (n= 165).

Although correlation was good for both TRUS and specimen volumes, they equally underestimated prostate weight with a large range of errors and poor concordance coefficients. Only 22% of TRUS volumes and 11% of calculated specimen volumes were within 10% of weight measurements. Application of a bullet-shaped mathematical model for prostates <55 g did not correct the large individual variation seen within these values.

Calculated prostate volume variables are prone to a large range of individual error regardless of the mathematical model used and should be avoided in statistical studies involving RP cohorts, and the more accurate prostate weight variable should instead be used as a size variable or correction factor.