ESTRO 2022 - Abstract Book

S1381

Abstract book

ESTRO 2022

reconstruction algorithm. A same-day 4D-CT (ten phases) was used as ground truth image for training and image- quality/dosimetric evaluation. Training of the neural network was performed with deformably registered pairs of 0% phase images of 4D-CBCT and 4D-CT. The dataset was split into a training (25 patients), validation (5) and test set (20). In the test set, image quality (mean absolute error, MAE and mean error, ME) and dosimetric accuracy (3%/3mm gamma analysis) were evaluated on the 0% (inhale) and 50% (exhale) phases. The proton dose distributions were generated by recalculating clinical 2-3 field IMPT treatment plans. Furthermore, we also compared MAE, ME and gamma results of 4D-sCTs to 3D-sCTs from a previous study with thorax patients. Results Figure 1 shows an overview of the 0% phase images of the 4D-CBCT, 4D-CT, and the 4D-sCT. An average MAE of 51.5 ± 5.6 HU and ME of 0.2 ± 5.2 HU were observed between 0% phase of 4D-sCT and 4D-CT. Evaluation of the 50% phase resulted in similar results (MAE: 52.4 ± 6.0, ME: 3.3 ± 5.3). The recalculation of clinical treatment plans resulted in average gamma pass ratios of 93.2 ± 3.0 % for the 0% phase and 92.5 ± 3.6 %. Figure 2 shows MAE and Gamma results of 0% and 50% phase for each patient. For comparison, 3D-sCTs resulted in an average MAE of 34.7 ± 7.2 HU and a gamma pass ratio of 93.9 ±