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Exploring a Novel Concept for Direct Proton Beam Measurement Via Its Magnetic Field: A Simulation Study

M Raedler* , G Dedes , K Parodi , M Riboldi , Ludwig-Maximilians-Universitaet Muenchen Department for Medical Physics (LS Parodi), Garching, BY


(Wednesday, 7/17/2019) 1:45 PM - 3:45 PM

Room: Stars at Night Ballroom 2-3

Purpose: To simulate the magnetic field (B) generated by a proton pencil beam (100 MeV) stopping in water. Simulation data are meant to serve as a benchmark for a novel measurement concept for a potential use in range verification based on optical magnetometry, which is deemed to reach the sensitivity necessary for this application.

Methods: We ran Monte Carlo simulations (Geant4) to extract the current density and the charge distribution of a proton pencil beam (15 nA) providing the input for the calculation of the magnetic field. Maxwell equations were solved numerically on a voxelized grid using an expanded magnetostatic finite element method (FEM).

Results: MC simulations and FEM can be combined for the estimation of B. We were able to show that the contributions from the time-dependent charge distribution B cannot be neglected, especially in an environment, where particles come to rest. B, approximately 5 cm off beam-axis, decreases smoothly and anti-symmetrically around the range of the beam Horizontal shifts can be detected due to the step-like shape of B around the range, whereas the signal is directly proportional to the current, potentially enabling real-time range verification.

Conclusion: The magnetic field generated by a proton beam can potentially qualify as a new method for beam monitoring and range verification. One major advantage is the approximate independence of the magnetic signal on its environment, as the permeability µ of biological tissue differs only slightly from the permeability of free space. The accelerator current used in our study yields very weak, but likely detectable, magnetic fields, yet cyclotrons are capable of producing significantly higher currents (800 nA) resulting in a proportionally higher B. Future activities will focus on experimental campaigns with a prototype, which is currently being assembled to provide proton beam measurements via optical magnetometry.

Funding Support, Disclosures, and Conflict of Interest: The work was supported by the DFG Cluster of Excellence Munich-Centre for Advanced Photonics (MAP)


Radiation Therapy, Image-guided Therapy, MRI


Not Applicable / None Entered.

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