Figure 5.

Panel (a) compares the lung mass as a function of respiratory phase in the original XCAT phantom with the lung mass after the implementation of the mass conservation scheme described in Sec. 2C. Panel (b) compares the ratio of energy in the dose distribution before and after deformation to a reference respiratory phase (full exhale) for the conventional radiation plan. The change in energy seen in the original XCAT phantom results from the lack of mass conservation as the chest expands during breathing. The residual energy- and mass-conservation defects in the mass conserving XCAT results are due to voxel size effects.