Introduction: Proton therapy is a treatment method for variety of tumors such as brain tumor. The most important feature of high-energy proton beams is the energy deposition as a Bragg curve and the possibility of creating the spread out Bragg peak (SOBP) for full coverage of the tumor. The aim of this study is the three dimensional (3-D) coverage of a brain tumor while healthy brain tissue absorbs less radiation.
 
Materials & methods: In this study, a spherical tumor with the radius of 1 cm in the brain is considered. A SNYDER head phantom has been irradiated with 86.5 MeV proton beam energy. APMMA modulator wheel and a PMMA range compensator wheel are used for longitudinal and lateral covering of the tumor, respectively. The simulations are performed using GEANT4 code.
 
Findings: Using a modulator wheel, the tumor is covered longitudinally and Spread Out Bragg Peak is created. In terms of lateral, in addition to the tumor, portions of healthy brain tissue are irradiated. 3-D coverage of spherical shape tumor is performed using a range compensator wheel. In the presence of modulator and range compensator wheels, the flux and absorbed dose of secondary particles produced by nuclear interactions of protons with elements in the head are considerably small compared to protons.
 
Discussion & conclusions: Using a modulator and a range compensator wheels the tumor can be treated accurately in the 3-D, so that the minimal damage reaches the surrounding tissues. The results show that more than 99% of the total dose of secondary particles and protons is absorbed in the tumor.