0SU-E-T-326: Assessment of 2D / 3D Intra-Fractional Tumor Motion for Respiratory-Gated Radiotherapy

Abstract

Purpose: This study aims to develop and evaluate the effectiveness of full 3-dimensional motion platform in respiratory-gated radiotherapy (RGRT) quality assurance (QA). For this study, a motion platform had been developed to simulate the patient specific QA in RGRT. Commercial motion platforms have the limited freedom of movement : lateral-longitudinal or vertical movement for tumor motion, and vertical movement for the external marker motion. Addition to these, the developed platform has the freedom of full 3-dimensional movement: simultaneous lateral, longitudinal as well as vertical motion for tumor motion. Methods: 3-dimensional tumor motions of ten abdomen cancer patients treated RGRT with no-motion, 2-dimensional 0motion, and 3-dimensional motion were extracted in phase sorted 4D-CT images. After deformable registration based on contoured image in 50% respiratory phase, the center of voxel was defined as the tumor position to trace its motion. Varian RPM log files were used to trace external markers. 3-dimensional tumor motions were simulated using the developed motion platform. On its polycarbonate panel, a radio-chromic film attached on 10 cm solid water slabs was placed for the dose verification. 2-dimensional and 3-dimensional tumor motions were performed with gated beam delivery to compare their dosimetric differences. The gating window was 35-65%. Gamma-index method was adopted to compare dose distributions of the measurement using radio-chromic film with those of treatment planning system. Results: The average gamma pass rates (2%/2 mm) were 96.11%, 89.69%, and 88.86% for static-continuous, 2D-gated, and 3D-gated, respectively. Excepting one case, static-continuous showed results over 94%. Some of 3D-gated resulted in pass rates larger than those of 2D-gated. Conclusion: 3-dimensional tumor motions showed lower gamma pass rates than those of 2-dimensional tumor motions during treatment. These imply the requirement of tools that provide the 3-dimensional tumor motion for QA in RGRT.