Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
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Feasibility Study of Patient Specific Quality Assurance Using Transit Dosimetry Based on Measurement with an Electronic Portal Imaging Device

  • Baek, Tae Seong (Department of Radiation Oncology, National Health Insurance Co. Ilsan Hospital) ;
  • Chung, Eun Ji (Department of Radiation Oncology, National Health Insurance Co. Ilsan Hospital) ;
  • Son, Jaeman (Department of Bio-convergence Engineering, Korea University) ;
  • Yoon, Myonggeun (Department of Bio-convergence Engineering, Korea University)
  • Received : 2017.06.30
  • Accepted : 2017.07.10
  • Published : 2017.06.30
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Abstract

This study was designed to measure transit dose with an electronic portal imaging device (EPID) in eight patients treated with intensity modulated radiotherapy (IMRT), and to verify the accuracy of dose delivery to patients. The calculated dose map of the treatment planning system (TPS) was compared with the EPID based dose measured on the same plane with a gamma index method. The plan for each patient was verified prior to treatment with a diode array (MapCHECK) and portal dose image prediction (PDIP). To simulate possible patient positioning errors during treatment, outcomes were evaluated after an anthropomorphic phantom was displaced 5 and 10 mm in various directions. Based on 3%/3 mm criteria, the $mean{\pm}SD$ passing rates of MapCHECK, PDIP (pre-treatment QA) for 47 IMRT were $99.8{\pm}0.1%$, $99.0{\pm}0.7%$, and, respectively. Besides, passing rates using transit dosimetry was $90.0{\pm}1.5%$ for the same condition. Setup errors of 5 and 10 mm reduced the mean passing rates by 1.3% and 3.0% (inferior to superior), 2.2% and 4.3% (superior to inferior), 5.9% and 10.9% (left to right), and 8.9% and 16.3% (right to left), respectively. These findings suggest that the transit dose-based IMRT verification method using EPID, in which the transit dose from patients is compared with the dose map calculated from the TPS, may be useful in verifying various errors including setup and/or patient positioning error, inhomogeneity and target motions.

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