Intensity‐modulated radiation therapy dose verification using fluence and portal imaging device

Abstract

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

Investigation of Error Detection Capabilities of Various Patient-Specific Intensity Modulated Radiotherapy Quality Assurance Devices

“…That was the reason the portal dosimetry system could detect the small magnitude of error than the other two QA devices. It was agreed with Sumida et al [8] studied whom suggested that the large target should use a finer resolution detector like portal dosimetry to compensate for the software interpolation data.…”

EPID-based daily verification of reproducibility of patients’ irradiation with IMRT plans

“…[7][8][9] Since these techniques are much more complex than conventional open-field 3DCRT (3D conformal radiotherapy), more advanced and precise quality control of treatment should be implemented. [1][2][3] In present clinical procedures, the pre-treatment dosimetry verification of IMRT plan is used at the hospital as https://doi.org/10.1016/j.rpor.2018.05.003 1507-1367/© 2018 Greater Poland Cancer Centre. Published by Elsevier Sp.…”

“…In recent years, EPID has gained new importance and usefulness in radiotherapy: it can be used not only for geometric verification of patient position or for preverification dosimetry but also as a useful tool for QA of linac: verification of output, geometry or MLCs. 3,4 There is also interest in transit dosimetry and patient dose reconstruction based on measurement fluency map collected during treatment. 2,6 It is easy to use and can be placed under treatment couch with patients lying on it.…”

IMRT dose verification considering passing rate and respiratory motion

“…This treatment requires high quality assurance and quality control. Dose verification for individual patients prior to treatment is required to ensure accurate treatment ( 3 ).…”