Perturbation effects of the carbon fiber-PEEK screws on radiotherapy dose distribution

Alexander Nevelsky, Egor Borzov, Shahar Daniel, Raquel Bar-Deroma, Alexander Nevelsky, Egor Borzov, Shahar Daniel, Raquel Bar-Deroma

Abstract

Radiation therapy, in conjunction with surgical implant fixation, is a common combined treatment in cases of bone metastases. However, metal implants generally used in orthopedic implants perturb radiation dose distributions. Carbon-Fiber Reinforced Polyetheretherketone (CFR-PEEK) material has been recently introduced for production of intramedullary nails and plates. The purpose of this work was to investigate the perturbation effects of the new CFR-PEEK screws on radiotherapy dose distributions and to evaluate these effects in comparison with traditional titanium screws. The investigation was performed by means of Monte Carlo (MC) simulations for a 6 MV photon beam. The project consisted of two main stages. First, a comparison of measured and MC calculated doses was performed to verify the validity of the MC simulation results for different materials. For this purpose, stainless steel, titanium, and CFR-PEEK plates of various thicknesses were used for attenuation and backscatter measurements in a solid water phantom. For the same setup, MC dose calculations were performed. Next, MC dose calculations for titanium, CFR-PEEK screws, and CFR-PEEK screws with ultrathin titanium coating were performed. For the plates, the results of our MC calculations for all materials were found to be in good agreement with the measurements. This indicates that the MC model can be used for calculation of dose perturbation effects caused by the screws. For the CFR-PEEK screws, the maximum dose perturbation was less than 5%, compared to more than 30% perturbation for the titanium screws. Ultrathin titanium coating had a negligible effect on the dose distribution. CFR-PEEK implants have good prospects for use in radiotherapy because of minimal dose alteration and the potential for more accurate treatment planning. This could favorably influence treatment efficiency and decrease possible over- and underdose of adjacent tissues. The use of such implants has potential clinical advantages in the treatment of bone metastases.

Keywords: Monte Carlo simulations; dosimetry; spinal implants; spinal radiotherapy.

© 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

Figures

Figure 1
Figure 1
CFR‐PEEK pedicle screw with thin titanium coating.
Figure 2
Figure 2
Definition of points around the screw model where the dose difference is reported.
Figure 3
Figure 3
(a) PDD curves in water with and without the presence of 3 mm plates of steel, titanium, CFR‐PEEK shown on the larger depth scale; (b) PDD curves and attenuation measurements for 1 mm plates; (c) PDD curves, attenuation and backscatter measurements for 3 mm plates; (d) PDD curves and attenuation measurements for 6 mm plates.
Figure 4
Figure 4
Map of the dose difference for the screws made of (a) Titanium, (b) CFR‐PEEK, (c) CFR‐PEEK‐TI; beam comes from above.
Figure 5
Figure 5
Map of the dose difference for the screws made of (a) Titanium, (b) CFR‐PEEK, (c) CFR‐PEEK‐TI; beam comes from the right side.
Figure 6
Figure 6
CT image of pedicle screws with titanium coating inserted into vertebra.

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