Application of Gafchromic EBT2 film for intraoperative radiation therapy quality assurance

Intraoperative radiation therapy (IORT) using electron beam is commonly done by mobile dedicated linacs that have a variable range of electron energies. This paper focuses on the evaluation of the EBT2 film response in the green and red colour channels for IORT quality assurance (QA).

The calibration of the EBT2 films was done in two ranges; 0-8 Gy for machine QA by red channel and 8-24 Gy for patient-specific QA by green channel analysis. Irradiation of calibration films and relative dosimetries were performed in a water phantom. To evaluate the accuracy of the film response in relative dosimetry, gamma analysis was used to compare the results of the Monte Carlo simulation and ionometric dosimetry. Ten patients with early stage breast cancer were selected for in-vivo dosimetry using the green channel of the EBT2 film.

The calibration curves were obtained by linear fitting of the green channel and a third-order polynomial function in the red channel (R2=0.99). The total dose uncertainty was up to 4.2% and 4.7% for the red and green channels, respectively. There was a good agreement between the relative dosimetries of films by the red channel, Monte Carlo simulations and ionometric values. The mean dose difference of the in-vivo dosimetry by green channel of this film and the expected values was about 1.98% ± 0.75.

The results of this study showed that EBT2 film can be considered as an appropriate tool for machine and patient-specific QA in IORT.