Accuracy and feasibility of sitting bladder volume measurement using portable ultrasound device in prostate radiotherapy.

This study evaluated the feasibility and accuracy of bladder volume measurement in the sitting position during prostate radiotherapy using a portable ultrasound device, compared with the conventional supine position. Forty patients (mean age 73.1 years; range 59-85) undergoing prostate radiotherapy were prospectively enrolled. Following planning CT (pCT), bladder volumes were measured using ultrasound in the supine position and immediately thereafter in the sitting position to minimize temporal variation. Reference bladder volumes were contoured on pCT images. Measurement error rates, correlations, and agreement (Bland-Altman, Wilcoxon signed-rank test) were evaluated. A predefined ± 15% margin, based on device specifications and clinical standards, defined clinically acceptable accuracy. Evaluated bladder volumes ranged from 99 to 435 mL. Mean differences between ultrasound and pCT volumes were - 25.9 ± 37.2 mL (supine) and - 12.2 ± 32.5 mL (sitting), corresponding to error rates of 14.1% and 9.1%, respectively. Strong correlations with pCT were observed in both positions (r = 0.89-0.92). Although a statistically significant difference was detected between positions (p < 0.01), the mean difference (supine minus sitting) was - 13.7 mL. The mean absolute difference between the two positions was 27.6 mL (median: 23 mL; range: 1-139 mL), and Bland-Altman analysis demonstrated agreement within the predefined margin. Bladder volume measurement in the sitting position demonstrated clinically acceptable accuracy for initial volume estimation. While not a perfect substitute for supine measurement due to individual variability, it serves as a practical tool for workflow optimization, such as pretreatment screening.