Bragg curve, dose distribution, and target fragmentation for thyroid proton therapy

Abstract

Information on energy deposition in human tissues and organs is of critical significance for proton radiation treatment planning. In the present paper, we studied the Bragg curves, dose distributions, and target fragmentations of proton therapy for a newly developed thyroid phantom. The phantom is considered to consist of 1.2 mm skin, 4.0 mm adipose, 6.0 mm skeletal muscle, 14.0 mm thyroid gland and 2.0 mm skeletal muscle. The Bragg curves were determined and compared by using three different simulations platforms namely Geant4, FLUKA, and PHITS at several proton energies. The obtained results showed that around 30 MeV, no energy deposition is observed at thyroid phantom and then the energy deposition rates of the layers at deeper (shallower) sides increases (decreases) as the proton energy increases. Moreover, we studied the production cross sections, due to the inelastic interactions caused by proton beam in the thyroid phantom, to quantify the contribution of target fragmentation. The fluence of each fragments at various depths in a thyroid phantom is also investigated and accurately scored. As a result, it is concluded that the target fragmentation is more important before the Bragg peak.