Room: Exhibit Hall | Forum 6
Purpose: To reconstruct real-time 4D CT images at each treatment moment by amplitude scaling of deformation vector fields (DVF) from planning 4D CT images (ASD 4DCT). The amplitudes of the moment are acquired from transit MV images during the treatment.
Methods: We created 4D CT images of an anthropomorphic digital phantom (XCAT) with a spherical lung tumor object (3cm in diameter) that moved with two different amlitudes of 1.02 cm and 1.83 cm (the former representing the time of planning CT acquisition and the latter that of treatment). Two actual patientsâ€™ respiratory patterns that differ significantly from each other, were used to model the movement. Temporal MV images through the two 4D images were acquired on our EPID model, previously developed, and were used to determine the amplitude and the phase of the patientâ€™s breathing at the time of planning CT and the moment, respectively. Note that the MV images of the latter phantom, not 4D CT images, at the moment are only available clinically. The ratio of the determined amplitude of the moment to that of the planning CT (scale factor) was multiplied to DVFs which represent movement of each image voxel at the pivot phase (i.e. maximum exhale) to that at the phase of the moment. The scaled DVFs were used to reconstruct the 4D CT images of the moment, and compared with the latter reference images.
Results: The scale factor was optimized for better agreement with the reference images (<1mm; dice indexes greater than 95.2% for all phases). The factor was smaller than the amplitude ratio by 9%.
Conclusion: The method of ASD 4DCT was developed to reconstruct the 4D CT images of the moment, and validated on a digital phantom. The reconstructed images may be used for 4D dose reconstruction and dose-adaptive therapy of lung.