SU‐E‐T‐430: Feasibility Study On Using Overlap Volume Histogram to Predict the Dose Difference by Respiratory Motion

Abstract

Purpose:The dose difference between three‐dimensional dose (3D dose) and 4D dose which considers motion due to respiratory can be varied according to geometrical relationship between planning target volume (PTV) and organ at risk (OAR). The purpose of the study is to investigate the dose difference between 3D and 4D dose using overlap volume histogram (OVH) which is an indicator that quantify geometrical relationship between a PTV and an OAR.Methods:Five liver cancer patients who previously treated stereotactic body radiotherapy (SBRT) were investigated. Four‐dimensional computed tomography (4DCT) images were acquired for all patients. ITV‐based treatment planning was performed. 3D dose was calculated on the end‐exhale phase image as a reference phase image. 4D dose accumulation was implemented from all phase images using dose warping technique used deformable image registration (DIR) algorithm (Horn and Schunck optical flow) in DIRART. In this study OVH was used to quantify geometrical relationship between a PTV and an OAR. OVH between a PTV and a selected OAR was generated for each patient case and compared for all cases. The dose difference between 3D and 4D dose for normal organ was calculated and compared for all cases according to OVH.Results:The 3D and 4D dose difference for OAR was analyzed using dose‐volume histogram (DVH). On the basis of a specific point which corresponds to 10% of OAR volume overlapped with expanded PTV, mean dose difference was 34.56% in minimum OVH distance case and 13.36% in maximum OVH distance case. As the OVH distance increased, mean dose difference between 4D and 3D dose was decreased.Conclusion:The tendency of dose difference variation was verified according to OVH. OVH is seems to be indicator that has a potential to predict the dose difference between 4D and 3D dose.This work was supported by the Radiation Technology R&D program (No. 2013M2A2A7043498) and the Mid‐career Researcher Program (2014R1A2A1A10050270) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning.