Feasibility study on the verification of actual beam delivery in a treatment room using EPID transit dosimetry

Seong S. Baek, Ji J. Chung, Jaeman Son, Myonggeun Yoon

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


Purpose: The aim of this study is to evaluate the ability of transit dosimetry using commercial treatment planning system (TPS) and an electronic portal imaging device (EPID) with simple calibration method to verify the beam delivery based on detection of large errors in treatment room. Methods and materials: Twenty four fields of intensity modulated radiotherapy (IMRT) plans were selected from four lung cancer patients and used in the irradiation of an anthropomorphic phantom. The proposed method was evaluated by comparing the calculated dose map from TPS and EPID measurement on the same plane using a gamma index method with a 3% dose and 3 mm distance-to-dose agreement tolerance limit. Results: In a simulation using a homogeneous plastic water phantom, performed to verify the effectiveness of the proposed method, the average passing rate of the transit dose based on gamma index was high enough, averaging 94.2% when there was no error during beam delivery. The passing rate of the transit dose for 24 IMRT fields was lower with the anthropomorphic phantom, averaging 86.8% ± 3.8%, a reduction partially due to the inaccuracy of TPS calculations for inhomogeneity. Compared with the TPS, the absolute value of the transit dose at the beam center differed by -0.38% ± 2.1%. The simulation study indicated that the passing rate of the gamma index was significantly reduced, to less than 40%, when a wrong field was erroneously irradiated to patient in the treatment room. Conclusions: This feasibility study suggested that transit dosimetry based on the calculation with commercial TPS and EPID measurement with simple calibration can provide information about large errors for treatment beam delivery.

Original languageEnglish
Article number273
JournalRadiation Oncology
Issue number1
Publication statusPublished - 2014 Dec 4

Bibliographical note

Funding Information:
This work was supported by the National Nuclear R&D Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education, Science and Technology (NRF-2013M2A2A7067089).

Publisher Copyright:
© Baek et al.; licensee BioMed Central Ltd.


  • EPID
  • Gamma index
  • Intensity modulated radiation therapy
  • Transit dose

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging


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