Measured dose perturbation around a Ti screw used in mandibular reconstruction from megavoltage electron beams

Data are presented for the measured dose perturbation produced by electron irradiation of a titanium screw used in mandibular reconstruction. These results show a decreased dose distal to the metal due to the electron interactions in the higher density material, an enhanced dose at the sides of the metal due to increased scatter from the higher Z material, and an increased dose proximal to the metal from backscatter. The magnitude and extent of these effects are shown to depend upon the electron energy, distance from the inhomogeneity and the dimensions of the inhomogeneity. Although the results for a single screw indicate that the magnitude and extent of these effects may not be clinically significant, the inclusion of from 2 to 6 of these screws in a radiation field could be clinically significant.