ESTRO 2024 - Abstract Book

S3282

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

right lung. The left lung tumor lesion displaced ± 0.7cm in the superior-inferior and anterior-posterior directions. The assessment of tissue densities for various tissues revealed the following density values: lung had densities of 0.2 g/cm3 in the phantom and 0.23 g/cm3 in the patient, bone exhibited densities of 1.3 g/cm3 in the phantom and a range of 1.16 to 1.45 g/cm3 in the patient, and soft tissue showed densities of 1.05 g/cm3 in the phantom and 1.026 g/cm3 in the patient. Additionally, the CT Hounsfield units (HU) were for lung: -716±108 (phantom) and -713±70 (patient); bone: 460±20 (phantom) and 458±206 (patient); soft tissue: 92±9 (phantom) and 60±25 (patient).The results from registering the bony anatomy in five 4DCTs and five gated CBCTs revealed a maximum displacement of 1mm in the superior-inferior (SI) direction for the tumor. The end-to-end testing, showed an excellent agreement for both large tumor (<0.2% for the motion encompassing and <1% of the gated treatment) and small tumor (<1% for the motion encompassing and <3.4% of the gated treatment) between the measured and the simulated doses in the Eclipse treatment planning system. Furthermore, the evaluation of global gamma pass rates revealed a high level of concordance for Gafchromic EBT3 film dosimetry. The gamma pass rates for both global and local normalization with different gamma criteria are shown in Table.1. The cut-off thresholds are 10% for both normalization methods. Figure 1. displays a comparison of the isodose overlays between the calculated and measured dose distributions of the small tumor for ITV plan on the left, and the gated plan covering phases from 10% to 90% on the right. The isodose patterns for both dynamic delivery techniques confirm the preservation of target coverage.