Study Finds Optimal Method For Prostate Volume Measurement in PI-RADS

Prostate volume plays an important role in the workup of suspected prostate cancer in addition to disease management. Traditionally, prostate volume was assessed by using ellipsoid measurements on ultrasound. However, this has been found to be user-dependent and has poor reproducibility. Prostate Imaging Reporting & Data System (PI-RADS) v2.1 allows for determining volume via segmentation or ellipsoid calculation. To further examine the ellipsoid and segmentation volume calculation methods, Dr Kiran R. Nandalur and his team conducted a study and evaluated if PSAd diagnostic performance is altered with ellipsoid and segmentation volume calculation methods.

In a retrospective study, the researchers included 397 men who underwent MRI and had recent pathology, with subset analysis of grade group 2 and higher and grade group 4 and higher. They determined prostate total volumes using ellipsoid calculations (TVe) and with semi-automated segmentation (TVs), along with inter-rater reliability with intraclass correlation coefficient (ICC). They calculated PSAd for TVe and created TVs and ROC curves to compare performance for Gleason ≥3 + 4 and ≥4 + 4 diseases.

Key findings of the study:

• Upon analysis, the researchers found that the traditional ellipsoid volumes significantly overestimated volumes with a mean of 55.4 mL vs 51.0 mL for segmentation volumes.
• For grade group 2 or higher disease, they observed that the two methods showed similar diagnostic performance with the area under the curve (AUC) of 0.63 for ellipsoid volumes and 0.64 for segmentation volumes.
• They noted that both methods demonstrated excellent inter-rater reliability with TVe with ICC of 0.93 and TVs with ICC of 0.9.
• However, for grade group 4 or higher disease, they found that the segmentation volume method outperformed the ellipsoid method, AUC was 0.61 for PSAd as derived from ellipsoid volume and 0.63 for segmentation.

The authors concluded, "Traditional ellipsoid measurements tend to overestimate total prostate volume compared to segmentation, but both methods demonstrate similar diagnostic performance of derived PSA density for PI-RADS clinically significant disease. "

They further added, "For higher grade disease, PSAd derived from segmentation volumes demonstrates statistically significant superior performance. Both methods are viable, but segmentation volume is potentially better."

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DOI:https://doi.org/10.1016/j.clinimag.2021.09.003