Abstract
GaToroid is a concept of toroidal gantry for hadron therapy under investigation at CERN It makes use of the toroidal magnetic field between each pair of coils to steer and focus the particle beams down to the patient. This peculiar concept requires detailed studies on particle tracking and beam optics to optimise the winding geometry and explore the properties of the system. The work presented in this manuscript is focused on the features of a GaToroid system for protons, specifically designed to minimise the footprint and weight of the gantry. Firstly, a two-dimensional single particle tracking was developed to optimise the coil geometry and the toroidal magnetic field, aiming to the maximisation of the energy acceptance of the magnet. Particles over the whole spectrum of treatment energy are directed at isocenter within 1 mm of precision. This procedure, restricted to the symmetry plane between each pair of coils, defines different beam orbits, function of the beam energy. Subsequently, a three-dimensional particle tracking was implemented to evaluate the interaction of a beam of finite dimensions with the complete magnetic field map in vacuum. The parameters of the simulated beam at the isocenter are coherent with the clinical requirements. The results of the three-dimensional tracking were then used to calculate the linear transfer matrix associated to each beam orbit. Finally, the option of performing the beam spot scanning at the isocenter by acting on the upstream steering magnet has been investigated, highlighting the potential of the concept, as well as the limitations related to the scanning field dimension and source-to-axis distance. In conclusion, the results described in this paper represent a crucial step toward the understanding of the beam optics properties of a GaToroid gantry.
Highlights
Hadron therapy is considered one of the most advanced and effective cancer treatment options based on radiation
The winding geometry was parametrised through the vector magnet position zV, internal bore radius Rin and ideal magnetic flux density B0, while the current distribution was modified subdividing the coils into 5 grades, i.e. planar sub-coils composing the winding, and adjusting their relative radial distance (Bottura et al 2020, Felcini et al 2020, Felcini 2021)
The results of the 2D particle tracking optimisation are presented in figure 3 for the complete energy range of proton treatments, i.e. 70–250 MeV, together with a magnetic field map produced by the whole torus in the symmetry plane between two coils
Summary
Hadron therapy is considered one of the most advanced and effective cancer treatment options based on radiation. Profiting from the sharp energy deposition, i.e. the Bragg peak typical of protons and heavy ions, it is possible to deliver a well-localised dosage of ionising radiation to the tumour cells, sparing healthy tissues from a large share of detrimental dose (Kraft 1990, Tsujii et al 2007, 2013, Durante and Orecchia 2017, Takada 2020) The downsides of this technology are the complexity, size and cost of the structures required to accelerate and direct particle beams down to the patient, namely accelerators and gantries. The potential of growth and societal impact are high motivators to study new concepts and techniques to deliver beams suitable for therapy using simpler, smaller and cost-effective machines This is especially true for heavy ions therapy, where the market penetration is still superficial and the margin for technological improvement and cost reduction is much larger (Yan et al 2016). To simplify the mechanics and lessen the overall weight, this concept allows directing the beam to the patient from a discrete number of directions avoiding, in principle, any rotation of the components
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