Objective Analysis of the Set-up Error and Tumor Movementin Lung Cancer Patients using Electronic Portal Imaging Device

Kim, Gwi Eon; Chung, Eun Ji; Lee, Chang Geol; Chu, Sung Sil; Kim, Woo Cheol

Abstract

PURPOSE: The aim of this study is to investigate the random and systematic errors and tumor movement using electronic portal imaging device in lung cancer patients for the adequate margin in the treatment planning of 3-dimensional conformal therapy.
METHODS
AND MATERIALS: The electronic portal imaging device is matrix ion chamber type(Portal Vision, Varian). Ten patients of lung cancer treated with chest irradiation were selected for this study. Patients were treated in the supine position without immobilization device. All treatments were delivered by an 10 MV linear accelerator that had the portal imaging system mounted to its gantry. AP or PA field portal images were only analyzed. Radiation therapy field included the tumor, mediastinum, and supraclavicular lymph nodes. A total of 103 portal images wereanalyzed for set-up deviation and 10 multiple images were analyzed for tumor movement because of respiration and cardiac motion.
RESULTS
The average values of setup displacements in the x, y direction was 1.41 mm, 1.78 mm, respectively. The standard deviation of systematic component was 4.63 mm, 4.11mm along the x,y axis, respectively while the random component was 4.17 mm in the x direction and 3.31 mm in the y direction. The average displacement from respiratory movement was 12.2 mm with a standard deviation of 4.03 mm
CONCLUSION
The overall set-up displacement includes both random and systematic component and respiratory movement. About 10 mm, 25 mm margins along x,y axis which considered the set-up displacement and tumor movement were required for initial 3-dimensional conformal treatment planning in the lung cancer patients and portal images should be madeand analyzed during first week of treatment, individually.