512 Evaluation of Computed Tomography Artefacts of Carbon-Fiber and Titanium Implants in Patients with Spinal Oligometastatic Disease Undergoing Stereotactic Ablative Radiotherapy

Aim This study evaluated artefacts on computed tomography (CT) images using Hounsfield units (HU) in patients with spinal oligometastatic disease (OMD) that received carbon fibre (CF) or titanium spine implants and underwent stereotactic ablative radiotherapy (SABR). Pre- and postoperative HU were measured at the vertebral body, pedicle, and spinal cord at three different levels: the lower instrumented vertebra, the level of metastatic spinal cord compression, and an uninvolved level. Method This retrospective single centre study included patients ≥18 years with spinal OMD who received CF or titanium spinal implants (including pedicles, screws, and rods) between 2018 and 2020.A closely matched gender and age group of patients that received CF (n=11) and titanium implants (n=11) was selected because gender- and age-related osteoporotic changes in bone density could potentially influence CT artefact measurements. Results Significant differences in HU were observed at the vertebral body, the pedicle, and the spinal cord at the lowest instrumented vertebra level for both CF and titanium (average increase 1.54-fold and 5.11-fold respectively). At the metastatic spinal cord compression level, a trend towards a higher HU-increase was observed in titanium compared with CF (average increase 2.51-fold and 1.43-fold respectively). Conclusions The relatively high postoperative HU-increase after insertion of titanium implants indicated CT artefacts, while the relatively low HU-increase of CF implants was not associated with artefacts. Therefore, we propose a CT artefact grading system based on postoperative HU-increase. This could be used in future studies to assess if less CT artefacts lead to better tumoricidal effects and decreased adverse effects after SABR.