ESTRO 2024 - Abstract Book

S3990

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2024

4DCBCT-based dose accumulation presented fraction-wise PTV under-dosages of up to 18% and up to 6% for the total dose, while 4DCT-based dose accumulation exhibited considerably less under-dosage (see Table 1). Further, it was possible to detect relevant inter-patient variations and to observe averaging-out effects over a 5 fraction treatment scheme. Dose compensation due to averaging-out effects becomes more critical for a 1-3 dose fraction scheme.

Conclusion:

Pre-treatment 4DCBT dose accumulation reveals latent target under-dosages and potentially allows for dose compensation in the subsequent dose fractions by treatment plan adaption. However, it is important to highlight that the presented results rely on the accuracy of the dose accumulation process, and uncertainties in this process still need to be quantified. Further, observed inter-patient variability needs to be analysed through patient classification (i.e. patients with instable correspondence model) and database extension.

Keywords: 4DCBCT, SBRT, Lung

743

Proffered Paper

Predicting anatomical change from planar X-rays for image-guided paediatric abdominal proton therapy

Ana-Cristina Ghica 1 , Mikaël Simard 2 , Jennifer Gains 3 , Pei Lim 3 , Catarina Veiga 1

1 University College London, Centre for Medical Image Computing, London, United Kingdom. 2 University College London, Department of Medical Physics and Biomedical Engineering, London, United Kingdom. 3 University College London Hospitals NHS Foundation Trust, Department of Oncology, London, United Kingdom

Purpose/Objective:

Setup errors and anatomical change can negatively impact the quality of radiotherapy dose delivery. This is particularly relevant in proton beam therapy where variations in bowel filling can lead to range shifts. Variations in gastrointestinal (GI) gas have been previously linked to dose degradation in planning studies. Although cone-beam computed tomography (CBCT) provides high-resolution 3D anatomical information, its high cumulative radiation dose exposure poses practical concerns, especially in paediatric cases. Orthogonal X-ray imaging, commonly used for patient positioning, is a low-ionising 2D alternative that could have a role in detecting internal anatomical changes. In