The Change of characteristic of Bragg curve by location of inhomogeneities

Proton beams have highly desirable depth-dose distribution for radiation therapy, mainly due to the superior conformation of the dose to the target volume. This conformation, however, is influenced by inhomogeneities placed in the path of the proton beam. Effects of inhomogeneities have been particularly concerning since the degradation of the Bragg peak curve. For the presence of inhomogeneities in the beam path, When proton beams pass through materials, the Bragg peak curve has complex changes due to multiple Coulomb scattering between inhomogeneous materials and proton beams, e.g., variation of the stopping power, dose perturbations, and shift of the Bragg peak and range. In this study, we describe our efforts to assess the influence of inhomogeneities on the Bragg curve. The place of the material causes energy mixing in the penetration path of proton beams. In the clinical situation, the actual dose distribution for proton beam is less steep because of the physical character of the proton beam. This can be formally described as a convolution of the stopping power of the proton and the Gausiian distribution because proton beams pass through a complex structure within the human body. Therefore, dose perturbation by location of inhomogeneities must be sufficiently considered to achieve the purpose of proton therapy.