Advantages of carbon fibre-reinforced polyetheretherketone over titanium implants in spine SBRT: a phantom evaluation

This study evaluates the clinical feasibility of spine stereotactic body radiotherapy (SBRT) in the presence of titanium and carbon fibre-reinforced polyetheretherketone (CFR-PEEK) spinal implants using custom 3D-printed phantoms. The investigation focuses on the dosimetric accuracy, imaging challenges, and achievable localisation precision. Customised 3D-printed phantoms incorporating titanium and CFR-PEEK implants were computed tomography (CT) scanned, with and without metal artefact reduction (MAR) algorithms. Localisation accuracy was tested using Elekta XVI CBCT and Brainlab ExacTrac Dynamic. The dosimetric accuracy of the Monaco treatment planning system (TPS) was assessed under simple geometric conditions and for clinically realistic VMAT plans. Patient-specific quality assurance and phantom-based measurements using ionization chambers and radiochromic film were performed to evaluate delivered dose accuracy. Both Image Guided Radiotherapy (IGRT) systems achieved sub-millimetre localisation accuracy, with maximum deviations of 0.3 mm observed for titanium implants. The Monaco treatment planning system (TPS) demonstrated accurate dose modelling, with deviations < 1% for CFR-PEEK and < 2% for titanium implants in simple homogeneous arrangements. In complex VMAT plan deliveries, dosimetric measurements showed stronger agreement with TPS predictions for CFR-PEEK implants, with deviations < 3%. Titanium-based plans exhibited greater deviations, with localised dose discrepancies exceeding clinical tolerances of 5%. The application of MAR algorithms reduced these discrepancies to < 5%, ensuring clinically acceptable dosimetric accuracy. CFR-PEEK implants enhance clinical workflows due to reduced imaging artefacts and smoother dose distributions, making MAR corrections unnecessary. For titanium implants, MAR is essential to achieve clinically acceptable dosimetric accuracy, highlighting the robustness of CFR-PEEK for spine SBRT.