Dose perturbation effect of metallic spinal implants in proton beam therapy
| Autor: | Indra J. Das, Mark W. McDonald, Chee-Wai Cheng, Y. Jia, Li Zhao |
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| Rok vydání: | 2015 |
| Předmět: |
Materials science
Proton Bone Screws Imaging phantom metallic spinal implants proton therapy Perpendicular Humans Radiation Oncology Physics Dosimetry Radiology Nuclear Medicine and imaging Instrumentation Proton therapy Titanium Spinal Neoplasms Radiation Phantoms Imaging Radiotherapy Planning Computer-Assisted Radiotherapy Dosage Prostheses and Implants Stainless Steel equipment and supplies Orthopedic Fixation Devices Ionization chamber Radiographic Image Interpretation Computer-Assisted Radiotherapy Intensity-Modulated Tomography Artifacts Tomography X-Ray Computed dose perturbation Algorithms Beam (structure) Biomedical engineering |
| Zdroj: | Journal of Applied Clinical Medical Physics |
| ISSN: | 1526-9914 |
| Popis: | 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 and 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. PACS number: 87.50.sj |
| Databáze: | OpenAIRE |
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