Simulating respiratory liver motion: Development and evaluation of a deformable phantom for radiotherapy testing.

PURPOSE: Respiratory motion during liver radiotherapy introduces geometric uncertainty in tumor targeting, which can lead to underdosing of the tumor and overdosing of adjacent healthy tissues. While adaptive radiotherapy offers a potential solution, its performance requires rigorous validation using physiologically realistic phantoms. This study developed a dynamic liver phantom that simulates respiratory-induced liver motion and deformation to serve as a platform for testing adaptive radiotherapy algorithm and clinical radiotherapy systems.

METHODS

Using patient imaging data, digital models of the liver parenchyma, vessels, and tumors were created. Three 3D-printed materials with distinct CT values ensured clear structural contrast. The components were assembled anatomically, with ten fiducial markers for spatial reference. The model was embedded in a sponge matrix to mimic soft tissue and enclosed in a rigid resin shell. A programmable motor drove respiratory-like motion. Biomechanical fidelity was assessed by measuring the parenchyma's elastic modulus and comparing it to real liver tissue.

RESULTS

At 30 mm motor displacement, the phantom deformed by 5.57 mm (superior-inferior), 1.78 mm (anterior-posterior), and 0.5 mm (left-right) on average. Elastic modulus was 22.70 kPa under small strain (vs. 34.31 kPa in real liver) and 119.42 kPa under large strain (vs. 171.47 kPa).

CONCLUSION

This phantom effectively replicates respiratory liver motion and deformation, offering a valuable platform for validating and improving the geometric accuracy of adaptive radiotherapy.