Validation and predictive modeling of a portable bladder scanner for precision bladder management in pelvic radiotherapy

OBJECTIVES: Validate the accuracy of a portable bladder scanner (Caresono PadScan HD5) against planning CT and demonstrate its clinical application to optimize bladder preparation in pelvic radiotherapy. METHODS: Two retrospective cohorts were analyzed: 114 patients assessed with HD5 and 111 historical controls. Agreement between HD5-measured volume (VHD5) and planning CT (VCT) was evaluated with correlation, regression, Bland-Altman, and paired tests. Initial CBCT repetition rates were compared between cohorts. Subgroup analyses (BV < 300 vs ≥ 300 mL; age < 65 vs ≥ 65 years); sex and multivariable linear regression with interaction terms explored predictors of measurement error. RESULTS: VHD5 correlated with VCT (r = 0.723, P < 0.001) but underestimated volumes (mean bias -34.39 mL). Underestimation was markedly greater at VCT ≥ 300 mL (-71.46 vs -18.64 mL, P < 0.001). Multivariable regression confirmed bladder volume (BV) as the primary driver, with an age-dependent interaction showing steeper underestimation in younger (< 65 years) patients (P < 0.001). Following HD5 implementation, initial CBCT repetition rates decreased from 48.7% to 22.8% (P < 0.001). CONCLUSIONS: HD5 enables reliable, though negatively biased, BV estimates. Embedding an age-stratified, moderate-fill workflow reduces repeat initial CBCT and standardizes bladder preparation. ADVANCES IN KNOWLEDGE: We quantify volume-dependent underestimation and an age interaction, and translate them into a predictive, age-stratified protocol that operationalizes HD5 measurements for routine pelvic RT bladder management.