Simulation of proton and photon depth dose distributions using FLUKA and PHIT

The most popular radiation therapy currently used for cancer treatment is photon radiation. Nevertheless, there is damage to normal tissue resulting from photon energy deposition. Proton therapy is an alternative radiation therapy currently being used in many countries due to its special depth dose distribution characteristic. In this study, the effects of beam parameters, i.e. initial energy and beam intensity, on the depth dose distribution of photon and proton were determined by using Monte Carlo simulations called PHITS and FLUKA. We also varied the medium which photon and proton projected into, i.e. water, soft tissue, and compact bone. The results show that when beam energy increases, the dose of photon also increases, while the dose of proton decreases. Furthermore, the doses of both photon and proton depend on the beam intensity and the type of media. Soft tissue gives similar results to water but different from compact bone due to the effects of their densities and compositions. We also modified the proton beam to cover the target region. In this study, we assume the target located at 6 - 8 cm from the surface of water. By modulating the peaks appropriately, the extent of the high-dose region can be widened to cover the target region together with a uniform dose. This modulated peak is called spread-out Bragg peak (SOBP). To obtain the SOBP from various mono-energetic beams, the dependences of beam energy and intensity on depth dose distribution mentioned previously were used to calculate the depth dose distribution of mono-energetic beams instead of using PHITS or FLUKA. To generate SOBP to cover this target region, the results show that the energies of the modulated beams at 87.59 - 103.25 MeV are required. The weighted intensities are 0.13 – 0.44 for the modulation of 4 beams and 0.03 – 0.38 for 10 beams.