ESTRO 2024 - Abstract Book

S3633

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

An ab initio model of the MapCHECK was designed from the manufacturer’s blueprint data to precisely represent the detector positions and attenuating materials thickness. The calculated dose was then compared to measurements through a gamma analysis with gamma criteria of 3%/2mm.

Results:

The plan quality of MBRT plans in standard SAD setups were not found to be significantly worse than shortened SSD setups. This can be observed in Fig 1a, where the mean DVHs for the 2 setups are almost exactly overlapping for all structures.

As part of the original VMAT treatment, bolus was required in 10 of the 22 patients. MBRT plans did not require bolus by virtue of the higher electron entrance dose as can be observed in Fig 2a and Fig2b. CTV coverage was found to be clinically equivalent between plans of either modality (Fig 1b), with V 50Gy of 97.9±0.2% and 98.1±0.6% for the MBRT and VMAT plans (p=0.34), respectively. Evaluating the absolute paired difference between doses to organs-at-risk in MBRT and VMAT plans, we observed lower V 20Gy to normal tissue in MBRT plans by 14.9±3.2% (p<10 -6 ). Similarly, V 50Gy to bone was found to be decreased by 8.2±4.0% (p<10 -3 ).