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Assessment of 2D / 3D Intra-Fractional Tumor Motion for Respiratory-Gated Radiotherapy

K Choi

J Lee1,2,3, Y Park4, K Choi1,2,3*, S Ye1,5, (1) Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Suwon, Korea, (2) Biomedical Research Institute, Seoul National University Hospital, Seoul, Korea, (3) Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea, (4) Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, (5) Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea,

SU-E-T-326 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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 motion, 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.

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