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.

 

 

 

Tae Seong Baek1,2, Eun Ji Chung2, Jaeman Son1 and Myonggeun Yoon1*

1Department of Bio-convergence Engineering, Korea University,
Jeongneungro 161, Seongbuk-gu, Seoul 136-703, Korea. 2Department of
Radiation Oncology, National Health Insurance Co. Ilsan Hospital, Ilsan, Korea.

 

Baek et al. Radiation Oncology 2014, 9:273