Monte-Carlo Study of Dose Contribution From Secondary Particles in MRI-Guided Proton Therapy
A BEN ALI*, M Majoros, X Zhang, E Collings, N Gupta, M Sumption, L Lu, The Ohio State University, Columbus, OH
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PO-GePV-M-314 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To investigate the dose contribution from the secondary particles generated in the interaction of proton beam particles with a phantom patient during the proton therapy under the environment of magnetic fields.
Methods: Monte Carlo code PHITS (v.3.26) was used to calculate the absorbed dose contributed from primary and secondary particles during proton therapy, using a single pencil beam along the Z axis, under the environment of magnetic field. A cylindrical water phantom was used to imitate the patient body. Two forms of a dipole magnetic field were used: 1) simple and uniform magnetic fields with different strengths in Y or Z axis direction; 2) magnetic field generated from our proposed and developed MRI system using medium temperature superconductors (MTS) and high temperature superconductors (HTS) technology.
Results: Without magnetic field, the dose contribution of protons in the total absorbed dose is about 99.44% at the maximum dose (Dmax). The contribution of secondary radiations (neutrons, electrons, photons, etc.) is less than 1%. Compared to By=0T, electrons contribution increase 1.69 to 2.34 times for By ranges from 0. 5 to 1.5T, with magnetic field in the Y direction (By≠0), and an increase up to 2.68 times with developed MRI system. A small change for others particles for both magnetic field forms.
Conclusion: Our result shows that the dose contribution of secondary particles at Dmax during proton therapy is about 1% to the total dose which varies with the strength of magnetic field.
Funding Support, Disclosures, and Conflict of Interest: The authors and the National Institutes of Health, as the funders of this work, have all copyrights. This work was supported by NIH under grant R01EB018363.
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