Dosimetry of very high energy electrons (VHEE) for radiotherapy applications : using radiochromic film measurements and Monte Carlo simulations

Subiel, Anna and Moskvin, V. and Welsh, Gregor H. and Cipiccia, Silvia and Reboredo Gil, David and Evans, P. and Partridge, M. and Desrosiers, C. and Anania, Maria Pia and Cianchi, A. and Mostacci, A. and Chiadroni, E. and Di Giovenale, D. and Villa, F. and Pompili, R. and Ferrario, M. and Bellaveglia, M. and Di Pirro, G. and Gatti, G. and Vaccarezza, C. and Seitz, Bjorn and Issac, Riju and Brunetti, Enrico and Wiggins, Mark and Ersfeld, Bernhard and Islam, Mohammad and Mendonca, M.S. and Sorensen, Annette and Boyd, Marie and Jaroszynski, Dino (2014) Dosimetry of very high energy electrons (VHEE) for radiotherapy applications : using radiochromic film measurements and Monte Carlo simulations. Physics in Medicine and Biology, 59 (19). 5811–5829. ISSN 0031-9155

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    Abstract

    Very high energy electrons (VHEE) in the range from 100-250 MeV have the potential of becoming an alternative modality in radiotherapy because of their improved dosimetry properties compared with MV photons from contemporary medical linear accelerators. Due to the need for accurate dosimetry of small field size VHEE beams we have performed dose measurements using EBT2 Gafchromic® film. Calibration of the film has been carried out for beams of two different energy ranges: 20 MeV and 165 MeV from conventional radio frequency linear accelerators. In addition, EBT2 film has been used for dose measurements with 135 MeV electron beams produced by a laser-plasma wakefield accelerator. The dose response measurements and percentage depth dose profiles have been compared with calculations carried out using the general-purpose FLUKA Monte Carlo (MC) radiation transport code. The impact of induced radioactivity on film response for VHEEs has been evaluated using the MC simulations. A neutron yield of the order of 10-5 neutrons cm-2 per incident electron has been estimated and induced activity due to radionuclide production is found to have a negligible effect on total dose deposition and film response. Neutron and proton contribution to the equivalent doses are negligible for VHEE. The study demonstrates that EBT2 Gafchromic film is a reliable dosimeter that can be used for dosimetry of VHEE. The results indicate an energy-independent response of the dosimeter for 20 MeV and 165 MeV electron beams and has been found to be suitable for dosimetry of VHEE.