Improving ultrasound-based prostate volume estimation

Abstract

Background To define a new coefficient to be used in the formula (Volume = L x H x W x Coefficient) that better estimates prostate volume using dimensions of fresh prostates from patients who had transrectal ultrasound (TRUS) imaging prior to prostatectomy. Methods The prostate was obtained from 153 patients, weighed and measured to obtain length (L), height (H), and width (W). The density was determined by water displacement to calculate volume. TRUS data were retrieved from patient charts. Linear regression analyses were performed to compare various prostate volume formulas, including the commonly used ellipsoid formula and newly introduced bullet-shaped formula. Results By relating measured prostate volumes from fresh prostates to TRUS-estimated prostate volumes, 0.66 was the best fitting coefficient in the (L x H x W x Coefficient) equation. This newfound coefficient combined with outlier removal yielded a linear equation with an R 2 of 0.64, compared to 0.55 and 0.60, for the ellipsoid and bullet, respectively. By comparing each of the measured vs. estimated dimensions, we observed that the mean prostate height and length were overestimated by 11.1 and 10.8% using ultrasound ( p < 0.05), respectively, while the mean width was similar ( p > 0.05). Overall, the ellipsoid formula underestimates prostate volumes by 18%, compared to an overestimation of 4.6 and 5.7% for the bullet formula and the formula using our coefficient, respectively. Conclusions This study defines, for the first time, a coefficient based on freshly resected prostates as a reference to estimate volumes by imaging. Our findings support a bullet rather than an ellipsoid prostate shape. Moreover, substituting the coefficient commonly used in the ellipsoid formula by our calculated coefficient in the equation estimating prostate volume by TRUS, provides a more accurate value of the true prostate volume.

Diagnostic performance of transrectal ultrasound for prostate volume estimation in men with benign prostate hyperplasia

“…Though cumbersome and probably impractical, a possible method for improving the performance of TRUS for prostate volume estimation is to take separate measurements of the median lobe and add its volume to the TPV. An alternative is to make a complete shift from the prolate ellipsoid formula to less popular options such as the spheroid or the bullet‐shaped formulae 3,30 . These newer formulae are, however, mostly not validated, and the added fact that most ultrasound machines in clinical use are already factory configured to calculate the prostate volume using the ellipsoid formula probably makes it even more difficult to completely dump this formula in practice.…”

“…Benign prostate hyperplasia (BPH) is a common urologic abnormality and remains a major source of morbidity, impaired quality of life, loss of man‐hours and rarely mortality in middle aged and elderly men worldwide 1 . Accurate determination of prostate volume is important for successful management of BPH because it predicts the risk of complications such as bleeding or urinary retention, guides choice of medical therapy, influences modality of surgery and has a role in monitoring following minimal invasive interventions such as prostate artery embolisation 2,3 …”

The end of “very low risk” in localized prostate cancer?

“…While the PIRADS v2 classification uses the coefficient of 0.52 to calculate prostate volume, other Diagnostic Imaging Specialists have opted for other coefficients, such as 0.65 and 0.66, believing these to be more accurate. 14 In fact, the last update of the PIRADS classification (2019 PIRADS v2.1) included changes in the calculated measurements for prostate volume. The midaxial plane is recommended for this measurement in PI-RADS v2, while the midsagittal plane is recommended in PI-RADS v2.1.…”

A comparison of how prostate volume obtained using transabominal ultrasound differs to volume obtained using transrectal ultrasound approach

“…Consequently radiation oncologists require precise measurements 13 . Radiation oncologists deem a patient suitable for brachytherapy if the prostate volume is over 60 cc 14 . This compares to volumes over 80 cc for stereotactic body radiotherapy (SBRT) 14 …”

“…14 This compares to volumes over 80 cc for stereotactic body radiotherapy (SBRT). 14 Assessment of prostate volume can be requested for elevated prostate-specific antigen (PSA). 15,16 PSA is a protein produced by the prostate.…”