Radiation dose perturbation at the tissue interface with PEEK and Titanium bone implants: Monte Carlo simulation, treatment planning and film dosimetry

Abstract

PurposeTitanium bone implants perturb the dose distribution in radiation therapy, creating additional considerations for planning and treatment. The relatively high scattering density of titanium gives rise to imaging artifacts in CT, making contouring difficult and necessitating post processing. While significant work has been undertaken to reduce the risk of implant failure through the introduction of porosity and the functionalization of the surface to improve osseointegration, the dose distribution within the voids of porous implant structures have not been investigated. Materials and methodsHere we demonstrate using Monte Carlo methods, a clinical treatment planning system (TPS) and film measurements that cavities within a titanium implant are associated with local spikes of dose (ranging from a 10–20% increase) which could impact the osseointegration of the implant. We propose an alternative material, poly-ether-ether-ketone (PEEK), which is emerging as a bone replacement material with attenuation properties closer to that of water. ResultsWe show that the reduced perturbation of both kV and MV beams by PEEK creates fewer artifacts in CT images and minimal enhancement of dose to tissue in voids. The significant dose enhancement at the entry interface and reduction of dose at the exit interface characteristic for titanium, are greatly reduced for PEEK. DiscussionThe dose perturbation associated with titanium on the exterior surface and within the voids, is of sufficient magnitude to warrant the surrounding tissue be considered an organ at risk (OAR).The reduced perturbation of the radiation beam caused by PEEK provides a far more hospitable environment for osseointegration and thereby, is likely to improve the success of implants for patients prescribed a course of radiation therapy.