title: Feasibility study on the verification of actual beam delivery in a treatment room using EPID transit dosimetry.
abstract: OBJECTIVE
  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
  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.
authors.affiliation: Department of Bio-convergence Engineering, Korea University, Jeongneungro 161, Seongbuk-gu, Seoul, 136-703, Korea. taesb@nhimc.or.kr.|Department of Radiation Oncology, National Health Insurance Co. Ilsan Hospital, Ilsan, Korea. taesb@nhimc.or.kr.
authors.forename: Tae Seong
authors.initials: TS
authors.lastname: Baek
authors.affiliation: Department of Radiation Oncology, National Health Insurance Co. Ilsan Hospital, Ilsan, Korea. ejchung@nhimc.or.kr.
authors.forename: Eun Ji
authors.initials: EJ
authors.lastname: Chung
authors.affiliation: Department of Bio-convergence Engineering, Korea University, Jeongneungro 161, Seongbuk-gu, Seoul, 136-703, Korea. jaeman0410@naver.com.
authors.forename: Jaeman
authors.initials: J
authors.lastname: Son
authors.affiliation: Department of Bio-convergence Engineering, Korea University, Jeongneungro 161, Seongbuk-gu, Seoul, 136-703, Korea. radioyoon@korea.ac.kr.
authors.forename: Myonggeun
authors.initials: M
authors.lastname: Yoon
mesh_terms: D000465:Algorithms; D002138:Calibration; D005240:Feasibility Studies; D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy; D019047:Phantoms, Imaging; D011785:Quality Assurance, Health Care; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*