Effects of implantable biomaterials on radiation dosimetry

Background. It is generally known that radiation dose is enhanced in front of and reduced behind metallic plates. This study evaluates metallic, ceramic, and bioabsorbable facial reconstruction materials for their differential effects on radiation dosimetry. Methods. Commercially pure titanium (cpt), stainless steel (steel), titanium alloy (tia), hydroxyapatite (HA), and poly-L-lactide (PLA, a bioabsorbable polymer) were obtained for this study. The radiation doses distal (behind) and proximal (in front of) to the test material were measured with an ionization chamber placed at several distances from the test material. Therefore, transmission (proximal to plate) and backscattering (distal to plate) factors were generated at several distances for each material. Results. Poly-L-lactide transmitted nearly 100% of the incident radiation beam. The metals had the greatest effect on transmission with steel, followed by cpt, tia, and HA showing the greatest reduction of incident beam. Poly-L-lactide revealed minimal backscattering. Greater backscatter of the incident radiation beam was seen from steel, followed by cpt and HA. Poly-L-lactide also behaved similar to water in transmission and backscatters properties during electron irradiation. Conclusions. Poly-L-lactide has a minimal effect on the radiation-dose distribution and may be beneficial as a reconstructive device for patients undergoing head and neck cancer radio therapy. Hydroxyapatite showed a relatively minor effect, whereas the metals (steel, followed by cpt and tia) revealed the greatest detrimental effect on the radiation-dose distribution.