The Effect of Proton and Helium Ions on Secondary Neutron Production in the Slab Head Phantom

Abstract

Particle therapy (PT) usually uses protons and carbon ions. In addition, the use of low-Z ions (such as He, O, Ne) with higher relative biological effects than protons is also being investigated. Although in PT the majority of the dose is delivered to the tumor volume by the primary particle, a negligible additional dose is left due to the contribution of secondary particles produced by the interaction between the therapeutic beam and the patient's tissues. In particular, neutrons can increase the risk of secondary cancer by transferring energy far away from the treated area. To use charged particles in radiation therapy, it is crucial to characterize secondary neutrons produced (SNP) as a result of primary particle interactions with human tissue. The SNP can be detected with the detector or by methods such as Monte Carlo (MC) simulation. In our study, the total number of neutrons produced in the slab head phantom by proton and He ion beams with an energy of 50-100 MeV/u, the doses stored by neutrons and all other particles were calculated with the Particle and Heavy Ion Transport Code System (PHITS) MC code. The number of SNP by He ion beam increased 7-14 times compared to proton beams. It was calculated that the doses of the SNP by protons were between 11.5% - 16.4% of those in the He ion beams.

Neutron shielding assessment of a 16O hadron therapy room by means of Monte Carlo simulations with the PHITS code

“…and compensators. Therefore, it is a very good approximation to neglect the secondary particle generation in the beamline and focus on the interaction of the primary beam with the patient [21].…”