Open AccessIntensity‐modulated radiation therapy dose verification using fluence and portal imaging device
Author(s) -
Sumida Iori,
Yamaguchi Hajime,
Das Indra J.,
Kizaki Hisao,
Aboshi Keiko,
Tsujii Mari,
Yamada Yuji,
Suzuki Osamu,
Seo Yuji,
Isohashi Fumiaki,
Ogawa Kazuhiko
Publication year - 2016
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1120/jacmp.v17i1.5899
Subject(s) - fluence , ionization chamber , detector , optics , nuclear medicine , image guided radiation therapy , dosimetry , beam (structure) , calibration , diode , quality assurance , materials science , physics , radiation therapy , ionization , medicine , optoelectronics , laser , radiology , ion , external quality assessment , pathology , quantum mechanics
Patient‐specific quality assurance for intensity‐modulated radiation therapy (IMRT) dose verification is essential. The aim of this study is to provide a new method based on the relative error distribution by comparing the fluence map from the treatment planning system (TPS) and the incident fluence deconvolved from the electronic portal imaging device (EPID) images. This method is validated for 10 head and neck IMRT cases. The fluence map of each beam was exported from the TPS and EPID images of the treatment beams were acquired. Measured EPID images were deconvolved to the incident fluence with proper corrections. The relative error distribution between the TPS fluence map and the incident fluence from the EPID was created. This was also created for a 2D diode array detector. The absolute point dose was measured with an ionization chamber, and the dose distribution was measured by a radiochromic film. In three cases, MLC leaf positions were intentionally changed to create the dose error as much as 5% against the planned dose and our fluence‐based method was tested using gamma index. Absolute errors between the predicted dose of 2D diode detector and of our method and measurements were 1.26 % ± 0.65 % and 0.78 % ± 0.81 % respectively. The gamma passing rate (3% global / 3 mm) of the TPS was higher than that of the 2D diode detector ( p < 0.02 ), and lower than that of the EPID ( p < 0.04 ). The gamma passing rate (2% global / 2 mm) of the TPS was higher than that of the 2D diode detector, while the gamma passing rate of the TPS was lower than that of EPID ( p < 0.02 ). For three modified plans, the predicted dose errors against the measured dose were 1.10%, 2.14%, and − 0.87 % . The predicted dose distributions from the EPID were well matched to the measurements. Our fluence‐based method provides very accurate dosimetry for IMRT patients. The method is simple and can be adapted to any clinic for complex cases. PACS numbers: 87.55.D‐, 87.55.km, 87.55.Qr, 87.57.uq