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.
 

• Studies carried out with synchrotron radiation have shown that micro-beam radiation therapy (MRT) has unique advantages in the treatment of cancerous tumors. In this method, the determination of dose distribution and calculation of peak to valley dose ratio (PVDR) are considered as the most important steps in treatment planning. The PVDR is a criterion to evaluate the destruction of cancer cells and protection of normal cells in the tissues surrounding a tumor.

 
Materials and Methods: Using a multi-slit collimator, planar sliced beams were generated in an X-ray generator in order to determine dose distribution in a multilayer phantom made of plexiglass. An ionization chamber was used to measure absorbed dose. Given the large size of the sensitive area of the chamber in comparison with the narrow beams, a mono-slit collimator made of tungsten with a slit of 0.3×7.5 mm² in its center was placed in front of the ionization chamber. Furthermore, by using Geant4 computer code, a model, including X-ray source, multi-slit collimator, phantom, mono-slit collimator, and detector, was designed to compare experimental and simulation results.
 
Findings: The investigation of dose distribution in the phantom with both methods indicated the presence of peaks and valleys. Given the low intensity of X-ray beam generated by the X-ray generator, and limited exposure time, the experimental errors were considerable. When using 1 mm (Air)+0.5 mm (W) collimator, PVDRs were obtained as 8.7 and 10.5 for ionization chamber and simulation, respectively, in the depth of 8 mm of the phantom. On the other hand, with a 1 mm (Air)+1 mm (W)  collimator, the values obtained for this parameter were 11.1 and 13.3 for ionization chamber and simulation, respectively.
 
Conclusions: Based on the results, a multi-slit collimator made of tungsten could produce multi-slice X-ray. The estimated dose distribution using the Geant4 code was more accurate than the one obtained through ionization chamber, which can be due to the possibility of using a detector in much smaller dimensions in the Geant4 code.