Technical note: creating a four-dimensional model of the liver using finite element analysis.

Finite element analysis and two liver CT scans were used to construct a four-dimensional (4D) model of the liver during breathing. A linear elastic, small deformation mechanical model was applied to one patient to obtain intermediate organ position and shape between exhale and inhale. Known transformations between anatomically defined subsections of the exhale and inhale liver surfaces were applied as constraints to the exhale CT liver model. Intermediate states were then calculated and time weighted to determine a 4D model of the liver as it deforms during the breathing cycle. This model can be used to calculate a more accurate dose distribution during radiotherapy.