A study on the effects of intrafractional changes in bladder volume on positional accuracy and target dosimetry in online adaptive radiotherapy for cervical cancer.

Abstract

BackgroundTo evaluate the impact of intrafractional bladder volume fluctuations on positional error in online adaptive radiotherapy (ART) for cervical cancer, and to explore the effects of intrafractional bladder change on target dosimetry.MethodsTwenty patients with cervical cancer receiving radical radiotherapy (45-50 Gy in 25 fractions) between June 2024 and July 2025 were enrolled. A total of 500 online ART fractions were delivered, with two cone-beam computed tomography (CBCT) scans (CBCT1 and CBCT2) obtained per fraction. Positional errors in lateral (Lat), longitudinal (Lng), and vertical (Vrt) directions were measured on both scans. Target volumes and organs at risk (OARs) were re-delineated on CBCT1 to generate ART plan, and non-optimized dose calculations were performed on CBCT2. Bladder volume change rate was calculated, and patients were stratified into low (60%) volume-change groups. Group differences in positional errors and target dosimetric parameters were analyzed using SPSS 25.0.ResultsThe three-dimensional positional errors measured by CBCT2 were significantly lower than those by CBCT1 (Lng: 3.50 → 0.80 mm, Lat: 2.10 → 0.40 mm, Vrt: 2.90 → 0.90 mm, P 0.05). In the Lng direction, positional errors increased sequentially across the low, moderate, and high volume-change groups (0.40 mm → 0.90 mm → 1.40 mm), with the low volume-change group showing significantly lower errors than the moderate and high volume-change groups (P 0.05). The target coverage rate of the low, moderate and high volume-change groups of bladder volume change rate showed significant changes (99.40% → 98.36% → 97.88%), and the low volume-change group was significantly higher than the moderate and high volume-change groups (P ConclusionsART can significantly improve the positional accuracy of radiotherapy for cervical cancer. Controlling the intrafractional bladder volume change rate within 30% can further reduce positional errors during ART and mitigate the risks of target dosimetric deviations.