Analysis of the sources of uncertainty for EDR2 film‐based IMRT quality assurance

Abstract

In our institution, patient‐specific quality assurance (QA) for intensity‐modulated radiation therapy (IMRT) is usually performed by measuring the dose to a point using an ion chamber and by measuring the dose to a plane using film. In order to perform absolute dose comparison measurements using film, an accurate calibration curve should be used. In this paper, we investigate the film response curve uncertainty factors, including film batch differences, film processor temperature effect, film digitization, and treatment unit. In addition, we reviewed 50 patient‐specific IMRT QA procedures performed in our institution in order to quantify the sources of error in film‐based dosimetry. Our study showed that the EDR2 film dosimetry can be done with less than 3% uncertainty. The EDR2 film response was not affected by the choice of treatment unit provided the nominal energy was the same. This investigation of the different sources of uncertainties in the film calibration procedure can provide a better understanding of the film‐based dosimetry and can improve quality control for IMRT QA.PACS numbers: 87.86.Cd, 87.53.Xd, 87.57.Nk

Dosimetric investigation of breath-hold intensity-modulated radiotherapy for pancreatic cancer

“…Although the proportion of points required to pass the 3%/3 mm analysis was generally 90% when institutions had established acceptance criteria, there have been no studies to qualify these criteria as an apt "gold standard." In the present study, dose distributions were normalized to the maximum dose to reduce film uncertainties 19 and relative dose comparisons were performed using the following three criteria: 2%/1 mm, 3%/3 mm, and 5%/3 mm. While the crite-rion of 2%/1 mm is strict, this would be an important indicator for detailed evaluation of the dose distribution.…”

“…The delivered dose distribution under moving conditions was registered with that under stationary conditions based on the isocenter, as indicated by the four pinholes. The dose distribution was normalized to the maximum dose after using a calibration curve to reduce film uncertainties 19 and then compared for the area receiving more than 50% isodose to evaluate the dose around a target using the gamma index with dose difference/distanceto-agreement criteria (c D%/dmm ) of 2%/1 mm, 3%/3 mm, and 5%/3 mm. 20 Correlations between the c D%/dmm and key parameters listed in Table I, including ALPO and MU, were also analyzed.…”

Quality Assurance for Respiratory-Gated Radiotherapy Using the Real-Time Tumor-Tracking Radiotherapy System

“…The films were analyzed using commercially available radiation dosimetry software (DD systemversion 10.12; R'Tech Inc., Tokyo, Japan). The dose distribution was normalized to the maximum dose using a calibration curve to reduce film uncertainty [11].…”

Filmless methods for quality assurance of Tomotherapy using ArcCHECK

“…Ion chamber and film measurements with a manufacturer‐supplied Virtual Water cylinder phantom were widely used for dosimetry verification of patient treatment plans in helical Tomotherapy . However, film QA using EDR2 has been reported to be easily affected by the development process which introduces uncertainty to the calibration curve . Devices with 2D arrays also have successful applications in helical Tomotherapy QA despite the possible limitation due to its directional dependency .…”