ESTRO 2024 - Abstract Book

S4922

Physics - Quality assurance and auditing

ESTRO 2024

the first pCT and on treatment CBCTs for the empty protocol ([EP]; p=0.11), we found a significant difference when comparing the first pCT to on treatment CBCTs for the FP. There were significant decreases in bladder volumes between fraction 1 and fraction 20 across both protocols (137.8±19.4 vs 101.4±11.7 [EP] and 245.1±36.8 vs 150.1±22.2). For the empty bladder protocol, 58.6% of the total selected treatment plans were medium while 26% were small and 15.4% large. Conversely, 47% of the total plans chosen for the filling bladder protocol were small while medium plans were picked 30.5% of the time with large plans favoured 22.5% of the time. As expected, PTV volumes recorded for the empty protocol were smaller compared to the filling protocol for each PTV size, i.e., PTV_Sm [EP] vs PTV_Sm [FP]. Mean PTV_Med volumes (321.7±30.4) for the empty protocol were not significantly different (p=0.51) to the mean PTV_Sm volumes (355.0±39.7) for the filling protocol. No significant differences were found in PTV coverage for both protocols. OARs such as rectum and bowel loops were assessed at specific dose levels and found to be larger for the FP albeit not significant. However, the total volume of the body receiving these doses levels was significantly lower for the EP.

Conclusion:

Ultimately this work provides evidence in favour of an empty bladder protocol compared to a full bladder protocol. Interestingly, medium plans were selected more often for the EP compared to small plans being commonly preferred for the FP. We found smaller bladder volumes generated smaller PTVs, which led to reduced OAR and total body doses for the EP. Also, more consistent bladder volumes and reduced interfraction motion throughout the treatment course were recorded with EP. These results highlight improvements in dosimetry for patients who undergo an empty bladder protocol for MIBC.

Keywords: Adaptive bladder, filling protocols, audit

References:

1. Richters A, Aben K, and Kiemeney L. The global burden of urinary bladder cancer: an update. World J Uro. 2020;38:1895-1904.

2. Bladder cancer statistics | World Cancer Research Fund International (wcrf.org). Downloaded 24 Oct 2023.

2889

Proffered Paper

Risk Assessment of Patient-Specific Quality Assurance Methods for Particle Therapy

Daniel Robertson 1 , Christina Dahlgren 2 , Chin-Cheng Chen 3 , Heng Li 4 , Frank Emert 5

1 Mayo Clinic, Radiation Oncology, Phoenix, USA. 2 Skandion Clinic, Medical Physics, Uppsala, Sweden. 3 St. Jude Children’s Research Hospital, Medical Physics, Memphis, USA. 4 Johns Hopkins University, Radiation Oncology, Baltimore, USA. 5 Paul Scherrer Institut, Medical Physics, Villigen, Switzerland