Abstract
PurposeThe 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 materialsTwenty 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.ResultsIn 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.ConclusionsThis 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.
Highlights
The goal of radiotherapy is to deliver a therapeutic dose to a tumor volume while minimizing doses to surrounding organs [1,2,3]
We evaluated 24 intensity-modulated radiotherapy (IMRT) fields used in the radiotherapy of 4 randomly selected lung cancer patients
The passing rates were 96.6% and 95.4%, respectively, indicating that the transit dose map measured with the electronic portal imaging device (EPID) is well matched with the dose distribution calculated by the treatment planning system (TPS)
Summary
The goal of radiotherapy is to deliver a therapeutic dose to a tumor volume while minimizing doses to surrounding organs [1,2,3]. Efforts to achieve this goal have led to increasingly complex radiation delivery and dose calculation algorithms. An IMRT planning error in New York in 2005 caused a fatal radiation overdose resulting in the death of the patient [4]. This accident suggests that accurate verification of the dose delivered to the patient is essential for maximum treatment efficacy and to prevent accidental overdoses
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