Faculty Collaboration Database

Dose perturbation effect of metallic spinal implants in proton beam therapy. J Appl Clin Med Phys 2015 Sep 08;16(5):333-343

Date

12/25/2015

Pubmed ID

26699317

Pubmed Central ID

PMC5690149

DOI

10.1120/jacmp.v16i5.5566

Scopus ID

2-s2.0-84946912325 (requires institutional sign-in at Scopus site)   24 Citations

Abstract

The purpose of this study was to investigate the effect of dose perturbations for two metallic spinal screw implants in proton beam therapy in the perpendicular and parallel beam geometry. A 5.5 mm (diameter) by 45 mm (length) stainless steel (SS) screw and a 5.5 mm by 35 mm titanium (Ti) screw commonly used for spinal fixation were CT-scanned in a hybrid phantom of water and solid water. The CT data were processed with an orthopedic metal artifact reduction (O-MAR) algorithm. Treatment plans were generated for each metal screw with a proton beam oriented, first parallel and then perpendicular, to the longitudinal axis of the screw. The calculated dose profiles were compared with measured results from a plane-parallel ion chamber and Gafchromic EBT2 films. For the perpendicular setup, the measured dose immediately downstream from the screw exhibited dose enhancement up to 12% for SS and 8% for Ti, respectively, but such dose perturbation was not observed outside the lateral edges of the screws. The TPS showed 5% and 2% dose reductions immediately at the interface for the SS nd Ti screws, respectively, and up to 9% dose enhancements within 1 cm outside of the lateral edges of the screws. The measured dose enhancement was only observed within 5 mm from the interface along the beam path. At deeper depths, the lateral dose profiles appeared to be similar between the measurement and TPS, with dose reduction in the screw shadow region and dose enhancement within 1-2 cm outside of the lateral edges of the metals. For the parallel setup, no significant dose perturbation was detected at lateral distance beyond 3 mm away from both screws. Significant dose discrepancies exist between TPS calculations and ion chamber and film measurements in close proximity of high-Z inhomogeneities. The observed dose enhancement effect with proton therapy is not correctly modeled by TPS. An extra measure of caution should be taken when evaluating dosimetry with spinal metallic implants.

Author List

Jia Y, Zhao L, Cheng CW, McDonald MW, Das IJ

Author

Li Zhao PhD Associate Professor in the Radiation Oncology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Algorithms
Artifacts
Bone Screws
Humans
Orthopedic Fixation Devices
Phantoms, Imaging
Prostheses and Implants
Proton Therapy
Radiographic Image Interpretation, Computer-Assisted
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted
Radiotherapy, Intensity-Modulated
Spinal Neoplasms
Stainless Steel
Titanium
Tomography, X-Ray Computed