SU-E-J-145: Implementing 4D XCAT Phantom for 4D Radiotherapy Research

To characterize and implement the 4D Integrated Extended Cardiac Torso (XCAT) digital phantom for 4D radiotherapy (RT) application.

A computer program was developed to facilitate the characterization and implementation of the 4D XCAT phantom. The program can (1) generate 4D XCAT images with customized parameter files; (2) review 4D XCAT images; (3) generate composite images from 4D XCAT images; (4) track motion of selected region-of-interested (ROI); (5) convert XCAT raw binary images into DICOM format; (6) analyze clinically acquired 4DCT images and Real-time Position Management (RPM) respiratory signal. Validation of the motion tracking algorithm was made by comparing to manual method. Major characteristics of the 4D XCAT phantom were studied including the dependence of lesion motion on its location/size and inputted diaphragm profile. An end-to-end test from image generation to treatment planning was also performed.

The comparison between motion tracking and manual measurements of lesion motion trajectory showed a small difference between the two (mean difference in motion amplitude: 1.2 mm). The maximum lesion motion decreased nearly linearly (R2=0.97) as its distance to the diaphragm (DD) increased. At any given DD, lesion motion amplitude increased nearly linearly (R2 range: 0.89 to 0.95) as the inputted diaphragm motion increased. For a given diaphragm motion, the lesion motion is independent f the lesion size at any given DD. The 4D XCAT phantom can closely reproduce irregular breathing profile: the mean difference in motion amplitude between the inputted and the measured motion profile was 1.4 mm. The end-to-end test showed that clinically comparable treatment plans can be generated successfully based on 4D XCAT images.

An integrated computer program has been developed to generate, review, analyze, process, and export the 4D XCAT images. A robust workflow has been established to implement the 4D XCAT phantom for 4D RT application.