title: Experimental determination of electron source parameters for accurate Monte Carlo calculation of large field electron therapy.
abstract: Extensive work has been performed to validate Monte Carlo models for both photon and electron beams under standard conditions. However, for large field electron beam therapy, Monte Carlo simulations have not been able to provide good agreement when compared to the measured dose distributions. Since the accuracy of the calculation relies heavily on the geometry parameters of the linear accelerator and the characteristics of the incident electron beam, it is crucial to have a complete comprehension of these independent factors. In this work, the electron focal spot size for a CL21EX linac with various energies (6, 9, 12 and 16 MeV) was measured with a slit camera composed of alternating lead and paper sheets. For all the energies investigated, the electron focal spot is found to be elliptical and has a full width at half maximum (FWHM) ranging from 1.69 mm to 2.24 mm. A shift with respect to the crosshair was associated with each measured focal spot. In addition, we present an improved result for the large field in-air profile by utilizing a proposed divergent beam model in conjunction with the experimental focal spot dimension. This model can potentially provide a solution to the Monte Carlo validation of large field electron beam therapy.
authors.affiliation: Medical Physics Unit, McGill University, 1650 Cedar Ave Montreal, Quebec H3G 1A4, Canada. vhuang@po-box.mcgill.ca
authors.forename: Vicky W
authors.initials: VW
authors.lastname: Huang
authors.forename: Jan
authors.initials: J
authors.lastname: Seuntjens
authors.forename: Slobodan
authors.initials: S
authors.lastname: Devic
authors.forename: Frank
authors.initials: F
authors.lastname: Verhaegen
mesh_terms: D004583:Electrons; D009010:Monte Carlo Method; D016011:Normal Distribution; D010315:Particle Accelerators / Q000295:instrumentation*; D017785:Photons; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D012542:Scattering, Radiation