Supplementary Material for: Estimated prostate volume by semiautomatic segmentation of MRI is more accurately correlated with radical prostatectomy specimen weight than the volume calculated by ellipsoid formula

Background: Accurate in-vivo prostate volume (PV) estimation is important for obtaining prostate-specific antigen density (PSAD) and further predicting clinically significant prostate cancer (csPCa). We aimed to evaluate the accuracy of multiparametric magnetic resonance imaging (mpMRI) estimated PV compared to both volume and weight of radical prostatectomy (RP). Patients and Methods: We identified 310 PCa patients who underwent RP following combined targeted and systematic biopsy in our institution from September 2019 to February 2021. The MRI PV was determined using a semiautomated segmentation algorithm. Formula (prostate weight=(actual weight- 3.8g)/ 1.05 g/ml) was applied and the resulting volume was used in further analysis. RP PV was calculated using the prolate ellipsoid formula (width × height × length × π/6). Results: The median PV from MRI, RP and RP weight were 39 ml, 38 ml and 44 ml, respectively. Spearman's rank correlation coefficients (ρ) were 0.841 (MRI PV vs RP weight), 0.758 (RP PV vs RP weight) and 0.707 (MRI PV vs RP PV) (all p<0.001). Decreased correlation between the MRI PV and RP PV was observed in the larger (more than 55ml) prostate. The PSAD derived from MRI PV showed most efficient to detect csPCa in RP specimen (57.9% vs 57.6% vs 45.4%) Conclusion: MRI PV is correlated better with RP weight than calculated RP PV especially in larger prostate. The high csPCa detection rate in final pathology suggested that PSAD derived from MRI PV can be confidently used in clinical practice.