Investigating the Effect of Magnetic Field on Radiation Dose Distribution in Radiotherapy using Photon and Electron Beams of Linear Therapeutic Accelerators

Magnetic fields can be used in radiation therapy to reduce electron contamination and improve dose delivery accuracy. MRIgRT systems use magnetic fields to track the position of the tumor during treatment and precisely deliver the dose from electron beams to the tumor, which will lead to improved treatment outcomes and reduced side effects.

The MCNP 6.1 Monte Carlo code was used to simulate the Varian 2100 C/D LINAC in both photon and electron modes. Percentage depth dose curves, dose profiles, and the fluence of contaminating electrons and photons were calculated. Dose profile penumbra and dose differences were calculated for different modes. In the second phase of the study, a constant 1.5 Tesla longitudinal magnetic field was applied to a water phantom that was aligned with the direction of the radiation beam.

Results:

 The MD reduced the surface dose by 8.3% and the dose profile penumbra by 5.6% at the surface of the water phantom. The MD removes all contaminating electrons from the radiation field without affecting the number of photons. The application of a 1.5 Tesla longitudinal magnetic field increased the dose by 4% in the maximum dose depth region and reduced the penumbra by 20% and the off-axis dose by 57% at the same depth.

Conclusion:

 The MD reduces surface dose, off-axis dose, and dose profile penumbra. The longitudinal magnetic field reduces penumbra and off-axis dose in electron beams.