MO-A-213AB-04: Verification of 4D Dose Delivery Using 4D Digital Human Phantom

At present, techniques of 4D dose verification in radiation therapy for lung cancers associated with respiratory motion are very limited, due to either lack of patient anatomy or breathing information. The aim of this study is to develop a 4D dose verification technique based on XCAT phantom which incorporates both patient anatomy and respiratory mechanics.

The 4D-XCAT phantom which possesses patient specific anatomy and allows input of respiratory parameters was generated using an integrated Matlab program. 10-phase 4DCT, MIP, and AIP images generated from 4D-XCAT were used for designing a 3D conformal treatment plan. Real-time dose delivery was simulated by calculating the deposited dose in each phase of 4D-XCAT for each beam with fixed individual planning dose. The 4D delivered dose was determined by accumulating dose deposition of all beams in all phases using deformable image registration implemented in VelocityAl software. The planned and delivered doses were compared based on target coverage and DVHs of OARs (lungs, cord, heart, and esophagus).

Target volume coverage was 97.5% in the simulated real-time delivery, as compared to 95% as planned based on AIP. Maximum cord dose, maximum esophagus dose, mean heart dose, and V20Gy of lung were comparable between the planned and delivered dose; the relative difference were 0.3%, 4.0%, 0%, and 2.8%, respectively. These results indicates AIP-based planning was a close representation of the real 4D dose delivery for both target and OARs when the breathing pattern is regular and reproducible.

A framework has been successfully established for verifying 4D dose delivery using the 4D-XCAT phantom and deformable image registration. This verification method is capable of incorporating specific patient anatomy and respiratory mechanics.