Effects of the modulator and range compensator blades on Bragg curve and calculating the secondary particle dose in proton-therapy of thymus gland cancer using MCNPX, FLUKA and GEANT4 codes

The thymus gland is an endocrine gland that plays an important role in the body’s immunity. Thymus gland cancer happens very rarely and one treatment way is radiation therapy. Due to the location of this gland and its proximity to the sensitive organs, radiation therapy of thymus gland cancer will bring the risk of side effects. In this paper, a Mird phantom is simulated and a modulator and range compensator blades are designed to create a Spread Out Bragg Peak (SOBP) in the tumor region. The simulations are performed using the Monte Carlo GEANT4 toolkit, the FLUKA and MCNPX codes. Neutrons and photons have been considered as the most important secondary particles produced in the non-elastic nuclear interactions of protons with different elements of the body. The absorbed dose of protons and secondary particles produced during the proton therapy are calculated in the tumor, the healthy tissue of thymus gland and the 12 sensitive organs that located near this gland using these simulation tools. The results of different codes are in good agreement with each other. Results show that approximately 96 percent of the total dose is absorbed in the tumor region and the organs near the Thymus gland absorb a small amount of dose during the proton therapy.