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Original Article

Korean Journal of Medical Physics 2014; 25(2): 100-109

Published online June 30, 2014

Copyright © Korean Society of Medical Physics.

Development of New 4D Phantom Model in Respiratory Gated Volumetric Modulated Arc Therapy for Lung SBRT

폐암 SBRT에서 호흡동조 VMAT의 정확성 분석을 위한 새로운 4D 팬텀 모델 개발

KyoungJun Yoon*, JungWon Kwak*, ByungChul Cho*, SiYeol Song*, SangWook Lee*, SeungDo Ahn*, SangHee Nam

윤경준*ㆍ곽정원*ㆍ조병철*ㆍ송시열*ㆍ이상욱*ㆍ안승도*ㆍ남상희

*Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Department of Biomedical Engineering, Inje University, Kyongnam, Korea

*울산대학교 의과대학 서울아산병원 방사선종양학교실, 인제대학교 의생명공학대학 의용공학과

Received: April 25, 2014; Revised: May 23, 2014; Accepted: June 29, 2014

Abstract

In stereotactic body radiotherapy (SBRT), the accurate location of treatment sites should be guaranteed from the respiratory motions of patients. Lots of studies on this topic have been conducted. In this letter, a new verification method simulating the real respiratory motion of heterogenous treatment regions was proposed to investigate the accuracy of lung SBRT for Volumetric Modulated Arc Therapy. Based on the CT images of lung cancer patients, lung phantoms were fabricated to equip in QUASARTM respiratory moving phantom using 3D printer. The phantom was bisected in order to measure 2D dose distributions by the insertion of EBT3 film. To ensure the dose calculation accuracy in heterogeneous condition, The homogeneous plastic phantom were also utilized. Two dose algorithms; Analytical Anisotropic Algorithm (AAA) and AcurosXB (AXB) were applied in plan dose calculation processes. In order to evaluate the accuracy of treatments under respiratory motion, we analyzed the gamma index between the plan dose and film dose measured under various moving conditions; static and moving target with or without gating. The CT number of GTV region was 78 HU for real patient and 92 HU for the homemade lung phantom. The gamma pass rates with 3%/3 mm criteria between the plan dose calculated by AAA algorithm and the film doses measured in heterogeneous lung phantom under gated and no gated beam delivery with respiratory motion were 88% and 78%. In static case, 95% of gamma pass rate was presented. In the all cases of homogeneous phantom, the gamma pass rates were more than 99%. Applied AcurosXB algorithm, for heterogeneous phantom, more than 98% and for homogeneous phantom, more than 99% of gamma pass rates were achieved. Since the respiratory amplitude was relatively small and the breath pattern had the longer exhale phase than inhale, the gamma pass rates in 3%/3 mm criteria didn’t make any significant difference for various motion conditions. In this study, the new phantom model of 4D dose distribution verification using patient-specific lung phantoms moving in real breathing patterns was successfully implemented. It was also evaluated that the model provides the capability to verify dose distributions delivered in the more realistic condition and also the accuracy of dose calculation.

Keywords4D phantom, 3D print, Lung SBRT, Respiratory Gated VMA

Korean Society of Medical Physics

Vol.35 No.2
June 2024

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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