Room: AAPM ePoster Library
Purpose: To reconstruct three-dimensional cine-computor tomographic(cCT) images that represent the moments of therapeutic beam irradiation from planning four-dimensional (p4D) CT images.
Methods: Reference 4DCT images were generated using an anthropomorphic digital phantom with two significantly-different respiratory traces in their shapes and tumor motion extents in three different tumor positions (close to diaphragm, close to chest wall, and close to the center of lung), respectively (the latter CT images are noted as t4DCT). DVFs were acquired by image registration between a pivot phase (the end of exale) and other phases of the p4DCT images. Projection images for all phases were calculated through the p4DCT and the t4DCT images (we denote the projection images as p4DCT-P and t4DCT-P, respectively). On each projection image set, the motion amplitude of the visible tumor was quantified as the displacement of its center-of-mass coordinate at each phase from the coordinate at the pivot phase. The ratio of the amplitude on the t4DCT-P set to that on the p4DCT-P set was obtained for each phase and was converted to the scaling factor which were obtained from a lookup-table between amplitude ratios and DVF ratios. The scaled DVFs were then used to resample the p4DCT images generating images at the time of beam irradiation (b4DCT). The b4DCT images were compared with the t4DCT images.
Results: The reconstructed b4DCT images showed good agreement with the reference t4DCT with <1.5 mm error for 3-cm tumor and 1.9 mm for 1-cm tumor close to diaphragm at the center of mass for the significant variation of the respiratory trace we have adopted in this study. The disagreement at the tumors close to chest well and center of lung was less than 1.0 mm and 0.5 mm, respectively.
Conclusion: The method of amplitude scaling could reconstruct the cCT images from p4DCT images accurately.