Computer Simulation and Analysis of Three-Dimensional Tumor Geometry in Radiotherapy

Radiotherapy plays an important role in the treatment for patients with solid tumors. Recently, the advantages in high-precision radiotherapy enable focusing of higher radiation energy (dose) to the tumor region while minimizing unwanted radiation exposure to surrounding normal tissue to avoid radiation injury. Intensity-modulated radiation therapy (IMRT) varies the intensities and profiles of beams from various directions to fit the tumor size and shape. This technique greatly improves dose concentration on target region and normal tissue sparing. Image-guided radiation therapy (IGRT) uses advanced imaging technology such as on-board imaging system to achieve precise and accurate dose delivery. Many studies have reported inter-fractional organ motions and efficacy of IGRT in reducing targeting errors using daily CT images (Den et al. 2009, Wang et al. 2009, Houghton et al. 2009, Pawlowski et al. 2010, Varadhan et al. 2009, Greene et al. 2009). Owing to these techniques, errors in patient set-up and dose delivery can be reduced to some extent. However, as radiotherapy typically takes several weeks, tumor and normal tissues may deform due to therapeutic effect or loss of body weight during treatment period. Shapes and locations of the tumor and the surrounding organs would be quite different from those when the treatment was planned. This results in overdosage of surrounding normal tissue or underdosage of target region. To overcome this issue, it would be useful to precisely analyse and predict the changes in three-dimensional (3D) geometries of tumors and normal tissues through the treatment.