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Publications in Scientific Journals:

H. Fuchs, P. Moser, M. Gröschl, D. Georg:
"Magnetic field effects on particle beams and their implications for dose calculation in MR-guided particle therapy";
Medical Physics, 44 (2017), 3; 1149 - 1156.



English abstract:
Purpose: To investigate and model effects of magnetic fields on proton and carbon ion beams for
dose calculation.
Methods: In a first step, Monte Carlo simulations using Gate 7.1/Geant4.10.0.p03 were performed
for proton and carbon ion beams in magnetic fields ranging from 0 to 3 T. Initial particle energies
ranged from 60 to 250 MeV (protons) and 120 to 400 MeV/u (carbon ions), respectively. The resulting
dose distributions were analyzed focusing on beam deflection, dose deformation, as well as the
impact of material heterogeneities. In a second step, a numerical algorithm was developed to calculate
the lateral beam position. Using the Runge-Kutta method, an iterative solution of the relativistic
Lorentz equation, corrected for the changing particle energy during penetration, was performed. For
comparison, a c-index analysis was utilized, using a criteria of 2%/2 mm of the local maximum.
Results: A tilt in the dose distribution within the Bragg peak area was observed, leading to non-negligible
dose distribution changes. The magnitude was found to depend on the magnetic field strength
as well as on the initial beam energy. Comparison of the 3 T dose distribution with non-B field (nominal)
dose distributions, resulted in a cmean (mean value of the c distribution) of 0.6, with 14.4% of
the values above 1 and c1% (1% of all points have an equal or higher c value) of 1.8. The presented
numerical algorithm calculated the lateral beam offset with maximum errors of less than 2% with calculation
times of less than 5 ls. The impact of tissue interfaces on the proton dose distributions was
found to be less than 2% for a dose voxel size of 1 9 1 9 1 mm3.
Conclusion: Non-negligible dose deformations at the Bragg peak area were identified for high initial
energies and strong magnetic fields. A fast numerical algorithm based on the solution of the energycorrected
relativistic Lorentz equation was able to describe the beam path, taking into account the
particle energy, magnetic field, and material. 2017 American Association of Physicists in Medicine
[https://doi.org/10.1002/mp.12105]

Keywords:
carbon ion, characterization, ion beam therapy, magnetic field, MR, proton

Created from the Publication Database of the Vienna University of Technology.