Room: Exhibit Hall | Forum 3
Purpose: To investigate the effect of different magnetic fields on dose distribution in inhomogeneous medium and to find the relationship between the electron return effect and the magnetic field strength.
Methods: The Monte Carlo code EGSnrc was modified to accommodate simulations under different magnetic fields 0T, 0.35T and 1.5T.The input for all simulations is the point source with a realistic accelerator energy spectrum named mohan6. The source skin distance is 100cm and the beam size is 3Ã—3cmÂ², 5Ã—5cmÂ² and 10Ã—10cmÂ². The two kinds of phantoms are water-lung-water and water-bone-water with the same size of 20Ã—20Ã—30cmÂ³ and the density of lung and bone is 0.15 g cmÂ³ and 1.85 g cmÂ³. The depths of the boundary of water-lung and lung-water are 6cm and 20cm. 105 million particles are simulated in every simulation.
Results: The magnetic field results in an increase or decrease in the dose at the interface of inhomogeneous medium. For water-lung-water phantom, the average dose increase for all beams is observed for B = 0.35T, 1.5T of 3.15%, 24.39% at the boundary of water-lung, and the average dose decrease for all beams is observed for B = 0.35T, 1.5T of 11.89%, 53.32% at the boundary of lung-water. For water-bone-water phantom, the average dose decrease for all beams is 1.31%, 7.51% at the boundary of water-bone, and the average dose increase for all beams is 2.31%, 9.47% at the boundary of bone-water.
Conclusion: This work indicates the effect of different magnetic fields in inhomogeneous phantom. As the beam travels from high-density media to low-density media, the dose at the interface will increases. At the same time, the dose at the interface will decreases when the beam travels from low-density media to high-density media. Moreover, the ERE will increase in the interface at higher magnetic field strengths.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by (1) National Key R&D Program of China (NO.2017YFC0113200), (2) National Natural Science Foundation of China (NO.81571771 and 81601577), (3) Post-doctoral Science Foundation of China (NO.2016M592510), and (4) the Scientific Research Foundation for the Returned Overseas Chinese Scholars of school (LX2016N004).