ESTRO 2023 - Abstract Book

S1566

Digital Posters

ESTRO 2023

Conclusion The Halcyon dose delivery accuracy was found to be high for even complicated fields. The 4 mm gaps above showed a perfect match between measurements and simulations. Reaching to small 2 mm openings, some deviation was seen for the combo case. This dose difference might be due to uncertainty of the mechanical leaf gap value used for in the MC simulations, or the positioning of the stacked MLC leaves. In addition, one explanation could also be the known mechanical slack in the MLC leaf control (Kulmala et al, ESTRO 2022, [Poster]). This feature of a collimator design is significant especially when small fields and dual-layer MLC are introduced. Overall, the results show that the Halcyon treatment machine can deliver dose rather accurately on this millimetre regime.

Poster (Digital): New technologies

PO-1833 Study of radial waveguide design for a compact dielectric wall accelerator

M. Maher 1 , C.M. Lund 1 , J. Bancheri 1 , D.G. Cooke 2 , J. Seuntjens 1,3

1 McGill University, Medical Physics Unit, Montreal, Canada; 2 McGill University, Department of Physics, Montreal, Canada; 3 University of Toronto, Princess Margaret Cancer Centre, Radiation Medicine Program, Toronto, Canada Purpose or Objective To computationally model electromagnetic distortion in radial parallel plate waveguides. This work is part of an effort to refine the design parameters of the electromagnetic field delivery modules for a compact dielectric wall accelerator for proton radiotherapy. The field delivery modules, composed of high-voltage pulse-generating circuits and parallel plate waveguides, are stacked along the beam axis and sequentially deliver short-lived ( ∼ 1 ns), high-gradient ( ∼ 100 MV/m) electric field pulses as the particle bunch transits the device. The high-gradient electric fields promise a compact accelerator ( ∼ 3 m), but pose design challenges, especially in the context of electrical breakdown. The proposed radial geometry offers a passive field amplification, which alleviates the electrical stress on upstream circuitry. However, temporal distortions of the waveform also occur, which can lead to undesirable characteristics in the accelerating field (mainly related to longitudinal stability of the particle bunch). Understanding the impact that waveguide geometry and composition have on the distortions is crucial to selecting a design that is both feasible to construct and suitable for the acceleration of a clinical proton beam. Materials and Methods COMSOL Multiphysics (2D Axisymmetric, Transient Electromagnetic Waves) was used to model radial parallel plate waveguides. The waveguide was uniformly excited at the outer radius with a Gaussian voltage pulse ( f ), and the output pulse ( h ) at the inner radius was measured (Fig 1). The frequency response of the system ( G , i.e., frequency-dependent amplification factor), was calculated numerically (Eq 1) and studied for various geometric (inner radius r in , outer radius r out , plate separation d ) and material (relative permittivity ε r ) parameters (Fig 1).