Dosimetric characterization and use of GAFCHROMIC EBT3 film for IMRT dose verification

Abstract

Radiochromic film has become an important tool to verify dose distributions in highly conformal radiation therapy such as IMRT. Recently, a new generation of these films, EBT3, has become available. EBT3 has the same composition and thickness of the sensitive layer of the previous EBT2 films, but its symmetric layer configuration allows the user to eliminate side orientation dependence, which is reported for EBT2 films. The most important EBT3 characteristics have been investigated, such as response at high-dose levels, sensitivity to scanner orientation and postirradiation coloration, energy and dose rate dependence, and orientation dependence with respect to film side. Additionally, different IMRT fields were measured with both EBT3 and EBT2 films and evaluated using gamma index analysis. The results obtained show that most of the characteristics of EBT3 film are similar to the EBT2 film, but the orientation dependence with respect to film side is completely eliminated in EBT3 films. The study confirms that EBT3 film can be used for clinical practice in the same way as the previous EBT2 film.

Figure 1

EBT3 film multichannel calibration curves up to 7 Gy.

Figure 2

Net optical density vs. absorbed dose (a) and first derivative of sensitometric curves in the three channels of the film (b).

Figure 3

Sensitometric response (net optical density vs. dose) at different orientations of the film in the scanner.

Figure 4

Change of the film coloration as a function of the time since irradiation for eight different dose levels.

Figure 5

Variation of net optical density after 30 min, 1 h, 2 h, and 6 h compared to optical density 24 h after irradiation for eight different dose levels.

Figure 6

Energy (a) and dose rate (b) dependence of EBT3 film.

Figure 7

Γ analysis results of an example IMRT pelvis case obtained comparing the EBT3 dose maps scanned from both sides with the same calibration curve each other using $3\%-3\text{mm}$ (a) and $2\%-2\text{mm}$ (b) as DD and DTA criteria, and with the calculated dose maps (c) and (d) with $3\%-3\text{mm}$ criteria.

Figure 8

Statistical distribution of Γ index and EBT3‐to‐EBT2 dose profiles comparison for 6 MV highly modulated fields using $3\%-3\text{mm}$ as DD and DTA criteria.

Figure 9

Γ value maps and Γ index statistics obtained with EBT3 film for a H&N (a) and a pelvis (b) plan using $4\%-3\text{mm}$ as DD and DTA criteria.