Spinal Implants and Radiation Therapy: The Effect of Various Configurations of Titanium Implant Systems in the Single Vertebral Metastasis Model

Summary: In order to study the dose disturbances in the spinal canal following spinal irradiation, saw bone models of posterior instrumentation and/or anterior column titanium cage reconstruction, anterior instrumentation and anterior column reconstruction with titanium cage or bone cement were established with titanium implants; irradiated with 60Co and LINAC and dose changes were measured with thermoluminescent dosimeters. The majority of the implant and radiotherapy combinations did not result in clinically significant dose change in the canal.

Background: Combination of surgery and radiotherapy is a common clinical practice in management of spine tumors. Although it is known that metallic implants disturb radiotherapy beams, it has been a mystery how these disturbances reflect in case of spinal irradiation in the presence of a spinal implant. The aim of this study is to investigate the effect of various spinal implant combinations on the radiotherapy dose in a single level metastasis model.

Methods: Standard saw bones and the following spinal implant combinations were used, posterior instrumentation with or without anterior column titanium cage reconstruction, anterior instrumentation and anterior column reconstruction with titanium cage or bone cement. 60Co and LINAC irradiation was performed twice and thermoluminescent dosimeters were used to measure the dose changes at the spinal canal.

Results: The posterior instrumentation models resulted in 5 to 7 % decrease in the radiation dose delivered to the spinal canal at all energy levels, whereas the anterior instrumentation systems resulted in <1 %.

Conclusions: Our results demonstrate that spinal implants have variable dose perturbation effects depending on the spinal implant construct and the energy level of the radiotherapy beam. The majority of these changes are statistically different from the implant-free irradiation, but the clinical significance of these changes is questionable. However, in order to stay on the safe side, anterior instrumentation with anterior titanium cage reconstruction system,which has the least dose perturbation effect, should be the implant of choice.