Modeling of the Liver Deformation During Breathing in Radiation Therapy

Abstract

Radiation treatment of liver cancer is challenging because the liver and the neighboring organs such as the stomach, small bowel, and esophagus should receive a minimum dose. The localization of the tumor at the treatment session is an important stage to define the dose for the tumor and for the neighboring normal tissue. The localization of liver tumor is very challenging because of the changes to the liver anatomy due to stomach filing, patient positioning, and breathing motion. During breathing, the shape of the liver changes. This change can vary from one person to another and can even vary from day to day for the same person. Image registration can be used to connect treatment images with planning images to define the changes during breathing motion for tumor localization. In this work, thirty patients were studied. First, we created a model for every individual patient by comparing the deformation in the end-exhale position image to that in the inhale position image. Thirty models were created. The displacement field map was calculated for each model, and it was found that the maximum displacement is toward the superior/inferior direction. After that, preprocessing steps for each patient were conducted to create the mean population model. The first step was drawing a manual contour for each end-exhale phase for each patient. Then, one patient was chosen to be the reference patient. After that, the MORFEUS algorithm was performed to align every patient to the reference patient. We did apply linear interpolation to put all patients in the same orientation. We also found the average displacement for the population to create a final global model of the liver. This result will help to improve the treatment of liver cancer.