Computational Simulation of Three-dimensional Tumor Geometry during Radiotherapy

Abstract

In Radiotherapy, shapes of tumors are important information to determine irradiation area and energy. In this study a simulation method is proposed to calculate changes of tumor geometry during radiotherapy. Relationships between tumor geometry and the amount of radiation energy were estimated from fundamental equations in solid mechanics as a mechanical analogy. Parameters between the radiotherapeutic effect and the geometric factor were defined as reduction resistance and reduction ratio. The values of these parameters were initially determined based on a widely-used radiobiological model (Linear-Quadratic model) and then revised by comparing with the change of actual tumor shape. To simulate uneven tumor shrinkage, the values of reduction resistance were varied depending on the tumor heterogeneity. Finite element models of tumors were constructed from CT images taken before the start of radiotherapy. For precise assessment of therapeutic effect, it would be useful to examine tumor morphological features. Three-dimensional (3D) tumor shape was represented in twodimensional (2D) map like a global map. Distances from origin (center of gravity of the tumor) to surface were visually indicated by colors in this map. Tumor volumes were indicated by sizes of the maps. Tumors in head and neck were analyzed in this study. Simulation results of tumor geometries were compared with actual tumor geometries and found to have similar tendencies. The 2D color maps enabled to evaluate the 3D morphological features of the tumors. Therefore this study provides the methodology to evaluate changes of 3D tumor geometry during radiotherapy. © 2009 International Federation of Medical and Biological Engineering.