Room: AAPM ePoster Library
EBT3 film is a widely used dosimetry tool. However, the film is recommended to be calibrated every half a year or even three months due to the aging effect of the unexposed film. This poses additional work for the physicists. To perform recalibration, a new method is proposed using an adaptive power function and no dose delivery is needed.
EBT3 film was calibrated four times at different dates with the last calibration date about eight months after the first. The dose-dependent optical density (OD) of the red channel was fitted to the delivered dose using a power function with a constant fitting parameter. In contrast to common methods of recalibrations, for which irradiations are required, the proposed method can calculate film-dose using only the fitting parameters of the first calibration and adapting the constant parameter using newly measured background OD. The film-dose calculated by the proposed adaptive method is compared with the given dose as percentage differences. Similar comparisons are also made using all new recalibrated fitting parameters and using only the first fitting parameters.
The results demonstrate that the difference between the film-dose with the delivered dose using the adaptive calibration method is within 3%. In contrast, if using the first calibration fitting parameters, the difference is greater than 50% for the delivered dose around 50 cGy when the film calibration date is eight months after the first calibration.
The film-dose can be calculated using the fitting parameters obtained from the first calibration together with the newly measured background OD to adapt the constant fitting parameter. With this method, recalibrating the film is not needed. To calculate the film-dose, the equation can be adapted specifically for each individual film at the time of usage. The presented method is convenient, time-saving and cost effective.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Ministry of Science and Technology of Taiwan (MOST 108-2221-E-214-006). The author declares that there is no conflict of interest.