Dosimetric evaluation of Gafchromic EBT2 film for breast intraoperative electron radiotherapy verification

Abstract

Purpose: Quality assurance (QA) is one of the most important issues that should be addressed for intraoperative electron radiotherapy (IOERT), which is not benefiting from image-based treatment planning system. The aim of this study is to evaluate the dosimetric characteristics of Gafchromic EBT2 film for breast IOERT QA procedure.

Methods: Due to the fact that some dedicated accelerators are being used for IOERT, dependence of the film response to energy, field size, dose rate and incidence angle of electron beam from the LIAC IOERT accelerator was studied. Then, film response curve to breast IOERT doses was obtained and its accuracy was evaluated and justified through comparison to the results of ionometric dosimetry.

Results: The results of this study indicated that there are no significant differences between the film responses at different energies of 6, 8, 10 and 12 MeV (P-value = 0.99). Similarly, no field size dependency was found when evaluating the response of the film to different field sizes ranging from 4 to 10 cm (P-value = 0.94). Film response was found to be independent of the dose rate of intraoperative electron beam (P-value = 0.12). Film response variations with changing the beam incidence angle were not significant (P-value > 0.8). Calibration curve at the dose range of 8-24 Gy had an acceptable accuracy. The difference between the results of film dosimetry and ionometric dosimetry was around 5% which was in agreement with the results of dose uncertainty estimation.

Conclusion: The EBT2 film was found to be a potentially appropriate tool for breast IOERT verification.

Keywords: Breast cancer; EBT2 film dosimetry; IOERT; Quality assurance.