Evaluation of the effect of gadolinium on dose enhancement factor of x-ray and gamma ray from linear electron accelerator

The aim of radiation therapy is to maximize the dose applied to the tumor while minimizing the dose in adjacent healthy tissues. A new approach to meet this requirement is using high atomic number materials to label the tumor site. In this study, gadolinium was used for this purpose. In the practical part of the research, the 6 MV gamma source of linear electron accelerator located in Milad Hospital of Isfahan and a cubic phantom containing water were used. The detector area, which houses gafchromic films, is a rectangular cube, which is the hypothetical location of the tumor and healthy tissues on either side of it and is located inside the phantom. Different concentrations of gadolinium were injected into the tumor area and the dose enhancement factor (DEF) was investigated in different areas of the detector. The phantom and detector were simulated using the Geant4 software package. The dose enhancement factors were calculated in different regions of the detector and for different concentrations of gadolinium irradiated with low energy X-rays, 2 MeV gamma rays (mean energy of linear electron accelerator) and the photon energy spectra of 6 MV linear. Study shows that the dose enhancement factor increases with increasing gadolinium concentration. The optimum energy for DEF at all concentrations of gadolinium is about 70 keV, and its effect decreases as the energy of the photon increases. In the energy spectrum of 6 MV we see fluctuations in the amount of DEF for different concentrations of gadolinium due to the presence of low and high energy spectra of photons.