Room: Track 5
To investigate the feasibility of using the magnetic field to confine and modulate high-energy electron beams to approach proton-like treatment.
We extended the in-house GPU-based Monte-Carlo simulation package to include charged-particle transport under external static magnetic fields. The arbitrary 3D magnetic field was modeled with three volumes (Bx, By, Bz) of the same dimensions as CT images. The process of electron inelastic/elastic interaction with material and trajectory deflection in the magnetic field was decoupled, where the deflection was calculated with relativistic Lorentz force at every simulation step and the magnetic field was tri-linearly interpolated. We simulated electron therapy for a wide range of representative beam energy (6, 18, 50 MeV) and field size (1, 5, 10 cm) in longitudinal and transverse magnetic fields (0.35T, 1.5T, 3T, 10T) at various modulation depth.
Increasing the strength in longitudinal magnetic field did not make a noticeable change until the strength was increased to 10T, in which case the penumbras (80-20%) at the 90% depth dose R_90, of the 10 cm field decreased from 0.7 cm to 0.3 cm, from 1.3 cm to 0.5 cm, and from 3.0 cm to 1.0 cm, for 6, 18, and 50 MeV beams, respectively. Both the 3T and 10T transverse fields truncated the depth dose curves and created the Bragg peak-like profiles at modulation depth R_80; in particular, the distal dose falloff R_(80-20) decreased from 8 cm (0T) to 1.5 cm (3T) and 0.5 cm (10T) for 50 MeV electron beams.
These results may lead to useful clinical applications since it can create proton-like treatment with high energy electrons and strong magnetic field. In addition, the magnetic depth modulation may be used with fixed electron beam energy for increased delivery flexibility.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by NIH grants (R01 CA235723, R01 CA218402).