A Mass-Conserving 4D XCAT Phantom for Dose Calculation and Accumulation

TL;DR

This paper introduces a mass-conserving 4D XCAT phantom that improves dose calculation accuracy in respiratory motion simulations, enabling more realistic dose accumulation assessments in radiotherapy.

Contribution

A novel framework enforces local mass conservation in the 4D XCAT phantom, enhancing the physical realism of dosimetric simulations and dose accumulation in respiratory motion studies.

Findings

Mass conservation alters lung dose distribution qualitatively.

DVH curves are not significantly affected by mass correction.

Differences of up to 10% in dose distribution regions were observed.

Abstract

The XCAT phantom is a realistic 4D digital torso phantom that is widely used in imaging and therapy research. However, lung mass is not conserved between respiratory phases of the phantom, making detailed dosimetric simulations and dose accumulation unphysical. A framework is developed to correct this issue by enforcing local mass conservation in the XCAT lung. Dose calculations are performed to assess the implications of neglecting mass conservation, and to demonstrate an application of the phantom to calculate the accumulated delivered dose in an irregularly breathing patient. Monte Carlo methods are used to simulate conventional and SBRT treatment delivery. The spatial distribution of the lung dose was qualitatively changed by the use of mass conservation; however the corresponding DVH did not change significantly. Comparison of the delivered dose with 4DCT-based predictions shows similar lung metric results, however dose differences of 10% can be seen in some spatial regions. Using this tool to simulate patient treatments reveals differences between the planned dose and the calculated delivered dose for the full treatment. The software is freely available from the authors.