Calcalation of brain and thyroid radiation scattered absorbed dose due to proton therapy of eyes using MCNPX simulation code

 Proton therapy is most  advanced treatment telepathy. protons evacuates  maximum energy in position called Bragg peak. Therefore, to treat  cancer, the tumor must be placed at the Bragg peak or SOBP. scattered photons and neutrons is a challenge in proton radiotherapy. purpose this study was to calculate dose of scattered photons and neutrons from eye in proton therapy .

 In this study, simulations was performed based on MCNPX code. For this, a spherical tumor with 0.6 cm diameter is considered in the eye phantom at a depth of 2.5 mm and bragg peak is formed excactly at the end of tumor. The eye phantom is irradiated with a proton with energy  50MeV.

 results show that  dispersed dose of  neutrons and photons due to proton therapy  in eye tissue are 8.817e-14 Gy and 1.653e-13 Gy respectively, and dose of the esophagus and thyroid are 1.037e-07 Gy and 2.89e-08 Gy for the dispersed neutrons respectively, and for photons 5.11e-08 Gy and 1.58e-07 Gy.

 The results show that  in the esophagus and thyroid is insignificant dispersal dose . The scattered dose of thyroid is  higher than that of esophagus, due to the proximity of this tissue to the radiation site. The results showed that less than 1% o total  proton dose  was dispersed  to other tissues.