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Design and Simulation of a Short, 10 MV, S-Band Linear Accelerator

D Baillie

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

TU-E-108-11 Tuesday 2:00PM - 3:50PM Room: 108

Purpose: To design a short (27.5 cm) S-band linear accelerator capable of producing a 10 MV x-ray beam to enable higher photon energies for linear accelerator-MRI hybrid systems, where the waveguide length and linac-MR orientation is a concern.

Methods: Finite element software COMSOL Multiphysics was used to design an accelerator cavity matching one published in an experiment on breakdown, to ensure that the threshold electric field published are applicable to the final waveguide geometry. This cavity was used as the basis for designing an accelerator waveguide, and the full RF field solution within the waveguide was calculated. This RF solution and an electron-gun phase space generated using Opera3D/SCALA are input into electron tracking software PARMELA to compute the electron phase space striking the x-ray target. The resulting electron beam is used for Monte Carlo simulations to calculate PDD curves and the beam penumbra, and compared against those produced by a Varian 10 MV.

Results: The shunt impedance, Q factor, and ratio of peak-to-mean electric fields of the cavity were matched to those in the published study to within 0.1% error. After tuning the full waveguide, the peak surface fields are 207 MV/m, well below the breakdown threshold of 239 MV/m. The peak of the electron spectrum is centered at 10.4 MeV, with a width of 0.2 MeV, compared with 10.5 MeV and 0.3 MeV, respectively, for a Varian 10 MV linac. Monte Carlo results show dmax is 2.15 cm for a 10x10 cm² field and the penumbra is 5.0 mm wide at 10 cm depth, compared with dmax at 2.3 cm and 5.6 mm width for a Varian 10 MV linac.

Conclusion: This work demonstrates the design and modeling of a waveguide capable of producing 10 MV energy x-rays yet short enough to be compatible with a linac-MR system.

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