In vitro backscattering from implant materials during radiotherapy

It is a certainty that many of the patients now receiving dental implants will one day require radiotherapy if they have head and neck cancer. The purpose of this study was to examine the dose enhancement from backscattered radiation at implant/bone interfaces irradiated with high-energy 6 MV and 10 MV x-rays. Three commonly used implant materials, pure titanium, Ti-6Al-4V alloy, and a high gold content implant material of various thicknesses, were used to measure the dose enhancement caused by backscattered radiation. The relative ionization charges at implant/bone interfaces were measured at distances of 0, 1, 2, and 3 mm away from the implant material by insertion of 0, 1, 2, and 3 mm thick bone substitute disks between the implant material and an ionization chamber. The results indicated that the highest dose enhancement occurred at a distance of 0 mm from the implant/bone interface for all the materials studied. The Au-Cu-Ag implant material had more average relative dose than pure titanium or Ti-6Al-4V alloy. The backscattered electrons decreased as the thickness of the bone substitute (distance between the implant material and the ionization chamber) increased.