Dosimetry of very high energy electronsud(VHEE) for radiotherapy applications: usingudradiochromic film measurements andudMonte Carlo simulations

摘要

Very high energy electrons (VHEE) in the range from 100–250 MeV haveudthe potential of becoming an alternative modality in radiotherapy becauseudof their improved dosimetry properties compared with MV photons fromudcontemporary medical linear accelerators. Due to the need for accurateuddosimetry of small field size VHEE beams we have performed doseudmeasurements using EBT2 Gafchromic® film. Calibration of the film has been carried out for beams of two different energy ranges: 20 MeV and 165 MeVudfrom conventional radio frequency linear accelerators. In addition, EBT2 filmudhas been used for dose measurements with 135 MeV electron beams producedudby a laser-plasma wakefield accelerator. The dose response measurements andudpercentage depth dose profiles have been compared with calculations carriedudout using the general-purpose FLUKA Monte Carlo (MC) radiation transportudcode. The impact of induced radioactivity on film response for VHEEs hasudbeen evaluated using the MC simulations. A neutron yield of the order ofud10−5 neutrons cm−2 per incident electron has been estimated and inducedudactivity due to radionuclide production is found to have a negligible effect onudtotal dose deposition and film response. Neutron and proton contribution to theudequivalent doses are negligible for VHEE. The study demonstrates that EBT2udGafchromic film is a reliable dosimeter that can be used for dosimetry ofudVHEE. The results indicate an energy-independent response of the dosimeterudfor 20 MeV and 165 MeV electron beams and has been found to be suitableudfor dosimetry of VHEE.