Evaluation of an Epson flatbed scanner to read Gafchromic EBT films for radiation dosimetry

Abstract

Gafchromic EBT (EBT) films are becoming increasingly popular due to their advantageous properties. When flatbed colour scanners are used for film dosimetry, a good quality control of the scanning device is a crucial step for accurate results. The proposal of this work was to fully assess the performance of the scanner Epson Expression 10000XL in order to quantify all parameters and needed corrections to minimize dose uncertainties. A standard step tablet, with 32 steps and optical densities from 0.06 to 3.8, was used to check the scanner linearity. The scanner warming-up effect and reproducibility were evaluated by performing 30 consecutive scans plus 20 scans in 15 min intervals. The scanning colour modes: 24 and 48 bits and scanning resolutions from 50 to 300 dpi were tested. A Wiener filter with different pixels regions was applied with the purpose of reducing the film noise. All scans were made in transmission mode with a constant film orientation. The red colour channel was posteriorly extracted from the images to maximize readout sensitivity. Two EBT films were irradiated, perpendicularly and parallel to beam incidence, with a 6 MV photon beam with doses that ranged from 0.2 to 3 Gy. A polynomial expression was used to convert optical density into dose. Dose uncertainty was quantified applying error propagation analysis. A correction for the non-uniform response of the scanner was determined using five films irradiated with a uniform dose. The scanner response was linear until an optical density of approximately 1 which corresponds to doses higher than those of clinical interest for EBT films. The scanner signal stabilized after seven readings. Scanner reproducibility around 0.2% was obtained either with the scanner warm or cold. However, reproducibility was significantly reduced when comparing images digitized with the scanner at different temperatures. Neither the colour depth mode, the scanning resolution, the multiscan option nor the Wiener filter had a significant effect on the shape of the calibration curve. However, a reduction in dose uncertainty was possible by selecting appropriate reading parameters. These are a 48 bit colour depth, a 75 dpi resolution and repeating the scan four times. Finally, the two dimensional Wiener filter applied to a 3 x 3 pixel region to the red component of the image reduced the experimental scan uncertainty to about 0.5% for doses higher than 0.5 Gy. Total scan uncertainty was less than 2% for a perpendicular calibration and reduced to less than 1% for a parallel calibration. A dose over-estimation of around 5% for clinical doses may be made if the image acquired is not corrected for the non-uniform response of the scanner. A protocol to read EBT films using the Epson Expression 10000XL scanner was established for IMRT verification. The contribution for the overall uncertainty in film dosimetry coming from the scanning process was estimated to be around 0.5% for doses higher than 0.5 Gy when reading parameters are optimized. Total scan uncertainty achieved is about 2% ...

Gafchromic film dosimetry: Four years experience using FilmQA Pro software and Epson flatbed scanners

“…More discrepancies were observed for head-andneck patients (Table 1), due to the scanner lateral distortions. Using the A3-size Epson 10000XL (Table 2), gamma passing rates were improved for head-and-neck patients, due to the better spatial uniformity in the central area of the scanner bed [4].…”

Robust optimization of VMAT for lung cancer: Dosimetric implications of motion compensation techniques

“…The dose attributed to the film from the CBCT acquisition was considered negligible when analysing distributions of 6 Gy fractions and was not accounted for in the comparisons. Gafchromic EBT3 film (Ashland Advanced Materials, NJ, USA), of which the accuracy has been verified in numerous works,59, 60, 61, 62, 63 was used for measurements. Film scanning was performed with an Expression 10000XL flatbed scanner (Epson Group, Nagano, Japan) at 24 hr post irradiation.…”

Wiener Filter Used in the EBT2 Film for Radiation Therapy

“…A03171101B were used for this study. The film was scanned with 127 dpi (5 dots per mm) before irradiation (pre-scan), which is a good choice for spatial resolution on an Epson 10000XL scanner to generate the background tiff image [24].The 6 MV photon beam of anElecta Synergy clinical linear accelerator was used for this investigation (Fig. 2).…”