Interobserver Variability of Transrectal Ultrasound for Prostate Volume Measurement According to Volume and Observer Experience

OBJECTIVE. The purpose of our study was to evaluate the interobserver variability of transrectal ultrasound for prostate volume measurement according to the prostate volume and the level of observer experience. SUBJECTS AND METHODS. Endorectal sonography was performed independently by two experienced observers in 101 patients and by one experienced and one less experienced observer in 110 patients; the prostate volume was then measured using the prolate ellipsoid formula. The volume difference between observers was analyzed according to the mean measured prostate volume determined by the observers and according to the level of observer experience. RESULTS. The volume difference was greater in prostates with a mean measured volume >= 30 mL than in prostates with a mean measured volume < 30 mL (6.00 vs 1.51 mL in the experienced observers and 6.84 vs 3.99 mL in the experienced and less experienced observers) (p < 0.05). The frequency of volume differences > 5 mL was greater in prostates with a mean measured volume >= 30 mL than in prostates with a mean measured volume < 30 mL (between the experienced observers, 18% vs 1%; between the experienced and less experienced observers, 54% vs 25%) (p < 0.01 in both comparisons). The volume difference was greater between the experienced and less experienced observers (5.00 mL) than between the experienced observers (2.96 mL) (p = 0.01). The frequency of volume difference > 5 mL was greater between the experienced and less experienced observers (35%) than between the experienced observers (7%) ( p < 0.01). CONCLUSION. Prostate volume measurement by transrectal ultrasound may vary when patients have large prostates or observers have varying levels of experience.