Calculation of total dose and dose equivalent distribution in the treatment of lung cancer using MR-guided carbon therapy

Nowadays, in order to improve the accuracy of treatment in radiation therapy, there are many attempts to use magnetic resonance imaging (MRI) due to the advantages of excellent soft tissue contrast and ultra-fast pulse sequences. On the other hand, carbon-ion radiation therapy is developing rapidly due to the benefits of greater relative biological effectiveness (RBE) and the application in the treatment of some low linear energy transfer (LET) radiation-resistant tumors. The idea of using MRI guidance in treating carbon-ion, presents challenges including the dose perturbation in the patientchr('39')s body. For this purpose, in this study, using a Monte Carlo simulation, a rectangular phantom was modeled with various tissue layers simulating chest geometry of a patient with lung tumor. For the first time in this study, three-dimensional dose perturbation of a 220 MeV/nucleon realistic carbon-ion beam in the presence of two medium (1.5 Tesla) and high (3 Tesla) magnetic fields applied to the simulated tissue phantom, was compared with the non-field condition. Also, the distribution of the three-dimensional dose equivalent in the simulated heterogeneous phantom was calculated in the presence of a 1.5 Tesla (T) magnetic field. At the Bragg depth, no longitudinal displacement was observed for the centers of the dose and dose equivalent profiles affected by a 1.5 T field. The longitudinal displacement of the total dose profile in a 3 T field was calculated to be 1.1 mm. Furthermore, the amount of lateral deflection of the center of the dose and dose equivalent profiles in a 1.5 T field was equal to 1.7 mm, and the amount of lateral displacement of the center of the dose profile in a 3 T field, was calculated to be 3.3 mm. The results indicate that the dose perturbation are remarkable in the accuracy expected from carbon-ion radiotherapy guiding by MRI.