title: On the use of Gafchromic EBT3 films for  validating a commercial electron Monte  Carlo dose calculation algorithm.
abstract: This study aims to investigate the effects of oblique incidence, small field size and inhomogeneous media on the electron dose distribution, and to compare calculated (Elekta/CMS XiO) and measured results. All comparisons were done in terms of absolute dose. A new measuring method was developed for high resolution, absolute dose measurement of non-standard beams using Gafchromic® EBT3 film. A portable U-shaped holder was designed and constructed to hold EBT3 films vertically in a reproducible setup submerged in a water phantom. The experimental film method was verified with ionisation chamber measurements and agreed to within 2% or 1 mm. Agreement between XiO electron Monte Carlo (eMC) and EBT3 was within 2% or 2 mm for most standard fields and 3% or 3 mm for the non-standard fields. Larger differences were seen in the build-up region where XiO eMC overestimates dose by up to 10% for obliquely incident fields and underestimates the dose for small circular fields by up to 5% when compared to measurement. Calculations with inhomogeneous media mimicking ribs, lung and skull tissue placed at the side of the film in water agreed with measurement to within 3% or 3 mm. Gafchromic film in water proved to be a convenient high spatial resolution method to verify dose distributions from electrons in non-standard conditions including irradiation in inhomogeneous media.
authors: Sunshine Hospital Radiation Therapy Centre (Peter MacCallum), St Albans, VIC 3021, Australia. eujin.chan@petermac.org
authors: EuJin
authors: E
authors: Chan
authors: Jenny
authors: J
authors: Lydon
authors: Tomas
authors: T
authors: Kron
mesh_terms: D000465:Algorithms; D004583:Electrons; D005373:Film Dosimetry / Q000379:methods*; D006801:Humans; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D054928:Validation Studies as Topic