Characterization of scanning orientation and lateral response artifact for EBT4 Gafchromic film

Abstract

The purpose of this study was to investigate the impact of scanning orientation and lateral response artifact (LRA) effects on the dose-response of EBT4 films and compare it with that of EBT3 films. Dose-response curves for EBT3 and EBT4 films in red-green-blue (RGB) color channels in portrait orientation were created for unexposed films and for films exposed to doses ranging from 0 to 1 000 cGy. Portrait and landscape orientations of the EBT3 and EBT4 films were scanned to investigate the scanning orientation effect in the red channel. EBT3 and EBT4 films were irradiated to assess the LRA in the red channel using a field size of 15 × 15 cm² and delivered doses of 200, 400, and 600 cGy. Films were scanned at the edge of the scanner bed, and the measured doses were compared with the treatment planning system (TPS) calculated doses at a position 100 mm lateral to the scanner center. At a dose of 200 cGy, the differences in optical density (OD) in the red, green, and blue color channels between EBT3 and EBT4 films were 0.035 (24.8%), 0.042 (49.7%), and 0.022 (64.4%), respectively. The EBT4 film slightly improved the scanning orientation compared to the EBT3 film. The OD difference in the different scanning orientations for the EBT3 and EBT4 films was 0.015 (6.8%) and 0.007 (3.9%), respectively, at a dose of 200 cGy. This is equivalent to a 20 or 10 cGy variation at a dose of 200 cGy. Compared with the TPS calculation, the measurement doses for EBT3 and EBT4 films irradiated at 200 cGy were approximately 16% and 13% higher, respectively, at the 100 mm off-centered position. The EBT4 film showed an improvement concerning the impact of LRA compared with the EBT3 film. This study demonstrated that the response of EBT4 film to a dose in the blue channel was less sensitive and showed an improvement in the scanning orientation and LRA effects.

Keywords: Gafchromic EBT4; film dosimetry; lateral response artifact; scanning orientation effect.

FIGURE 1

Dose‐response curves as a function of irradiated dose for EBT3 and EBT4 films in the red, green, and blue color channels.

FIGURE 2

Dose‐response curves in the red color channel as a function of irradiated dose for (a) EBT3 and (b) EBT4 films in landscape and portrait orientation.

FIGURE 3

Lateral dose profiles acquired using EBT3 and EBT4 films in red color channel irradiated with (a) 200, (b) 400, and (c) 600 cGy doses, with a field size of 15 × 15 cm² open field. The measured profiles were acquired perpendicular to the scan direction. The absolute dose was calculated with a treatment planning system (TPS) to compare with film measurement. The 0 mm position corresponds to the center of the scanner.