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Redesign of a 6 MV Linear Accelerator Waveguide to Produce Energies Up to 10 MV

D Baillie

D Baillie*, J St. Aubin, B Fallone, S Steciw, Cross Cancer Institute, Edmonton, Alberta

MO-A-213AB-2 Monday 8:00:00 AM - 9:55:00 AM Room: 213AB

Purpose: To investigate the feasibility of producing a short, high-energy linear accelerator for use in a proposed hybrid linear accelerator magnetic resonance imager (linac-MRI).
Methods: A short 6MV waveguide was previously simulated in COMSOL and benchmarked against experiment. The simulated input power is increased from 2.5 to 7.5 MW to reflect replacing the magnetron power source with a commercially available klystron, and the RF fields within the waveguide are calculated. The RF solution is used as an input into PARMELA, an electron-tracking software, to calculate the electron energy and spatial distribution exiting the waveguide. The electric fields within the waveguide are compared with experimental thresholds for electric breakdown within the waveguide to determine the possibility of operation at increased input power. The energy spectrum of the electron beam incident on the target is analyzed for suitability for radiotherapy. Finally, some potential modifications to the simulated cavity dimensions and positioning are discussed, and a preliminary estimate of the effects on the electron distributions are analyzed.
Results: When the input power is increased, peak surface electric fields within the waveguide of 215 MV/m are calculated, below the threshold determined by experiment of 240 - 300 MV/m for similar resonant structures. The FWHM of the electron focal spot is shown to be 1.5 times larger than the focal spot from the unmodified waveguide. The maximum electron energy increases from 6.1 to 10.6 MeV and the spread of electron energies is 5 times larger than the original. The modifications to the first cavity are shown to reduce the focal spot and energy spread to be comparable to the unmodified waveguide.
Conclusions: It is feasible to produce a high-energy waveguide that is short enough for use in our linac-MRI. Slight modifications to the existing waveguide design will be required to optimize beam parameters for treatment.

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