Digital phantoms for evaluating the dosimetric Impact of MRI Geometric inaccuracy in SBRT planning for liver cancer in the presence of motion

Abstract

MRI is increasingly being used in radiotherapy applications for tumor delineation and tracking in the presence of respiratory motion.The purpose of this work is to investigate the impact of systemrelated MR geometric inaccuracies on dose distributions for liver stereotactic-body radiation therapy (SBRT) using digital phantoms.A methodology of generating digital phantom was developed and presented in this study. Based on this methodology, two types of digital phantoms were generated. The first type is composed of 3D shapes with well-known geometry while the second type is extracted from CT patient images. These digital phantoms were then deformed based on a previously calculated distortion map. Highly conformal volumetric (VMAT) modulated arc therapy plans were then optimized on the distorted dataset and transferred to the original dataset and dose distribution was analyzed. Dosimetric evaluation on these digital phantoms showed that the dose received by the original set of images was higher than the dose received by the distorted images. Results also showed that the difference in the DVH is inversely proportional to the target size.The methodology used in this study, represents an important technique allowing the assessment of the dosimetric impact of organ deformation for different anatomic sites as well as treatment techniques.