Purpose: In proton therapy (PT) for patients with head and neck cancer, dental metals are known to largely perturb the dose distribution compared to that in photon therapy. The dental metals are basically removed before PT but removing them are often difficult. If the dental metals are irradiated by the proton beam, these can be activated by protons or secondary neutrons. However, there are no reports on effects of the activated dental metals. We aimed to fundamentally investigate the effects of the activated dental metals using Monte Carlo simulation and measurement.
Methods: The beam data on 150 MeV proton beam with 60 mm spread-Out Bragg peak (SOBP) size was used. Ti alloy and 12% Au-Ag-Pd alloy that are used as standard dental material in Japan were placed in the SOBP center in water phantom. Radionuclides induced by the proton beam irradiation were identified using Particle and Heavy Ion Transport code System (PHITS) and DCHAIN. Also, gamma-rays emitted from the activated dental metals were counted by high purity germanium (HP-Ge) detector. In addition, dose enhancement caused by the activated dental metals was calculated by PHITS.
Results: The spectra of the activated dental metals obtained in HP-Ge detector had the same energy peaks as the radionuclides estimated by PHITS. In addition, the dose around Ti alloy and Au-Ag-Pd alloy increased slightly as compared with the prescription dose.
Conclusion: The radionuclides induced from the dental metals were mostly dominated by nuclides with short half-lives. The dose enhancement caused by the activated dental metals was significantly lower compared with the prescription dose.