Determination the dosimetric properties of scattering foil and scattering foil free electron beams in clinical linear accelerator

Producing the ideal therapeutic electron beams from a clinical linear accelerator (Linac), is crucial to optimize dose delivery in radiotherapy. The aim of this study was to investigate the properties of electron beams with and without the scattering foil.

Varian Linac 2100CD head was simulated by means of MCNPX-2.7 program. After validation with measured data, scattering foils were removed and then different dosimetric properties of 6 and 9 MeV electron beams such as depth dose percentage, dose profile, range, surface dose, dose rate and photon contamination were calculated and compared for field sizes ranging from 0.25×0.25 to 10×10 cm2 in three states with primary and secondary scattering foil (SF), without primary scattering foil (PSFF) and without primary and secondary scattering foil (SFF).

By removing the scattering foils, dose rates and surface doses were increased more than 25 times in 0.25×0.25 cm2 field, and in the bigger fields, it was less in 10×10 cm2 field, almost 4 times and the photon contamination is reduced by 20% times in 0.25×0.25 cm2 field. Also, Adjacent organs receive a lower dose, Because the dose profile curve was shrieked, it was almost 1cm in field 2×2 cm2 and less than 1cm in other fields. The dose profile flatness was diminished in scattering foil-free (SFF) mode which is not crucial for the small fields.

Removing scattering foil improves dosimetric properties of electron beams specially to treat the superficial tumors and for the small field radiotherapy.