Clinical Implementation of the Philips Orthopedic Metallic Artifact Reduction (OMAR) Algorithm for Proton Radiotherapy CT Simulations
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PO-GePV-M-79 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To commission the Philips Ingenuity TF PET/CT scanner orthopedic metallic artifact reduction (OMAR) algorithm to be used on CT simulations for proton radiotherapy treatment planning in the RaySearch RayStation treatment planning system.
Methods: The Gammex Model 647 Tissue Characterization Phantom was scanned using several clinical CT simulation protocols with varied parameters (e.g., reconstruction filter). Artifact correction efficacy on CT Hounsfield Units was evaluated in OMAR scans with metal inserts as compared to scans with no metal inserts. Proton plans were created on the non-OMAR and OMAR phantom CT scans to evaluate the effects on dose distributions. Patient CT simulations (bilateral hip implants, dental filings, ports and spinal rods) and resulting clinical proton treatment plans were compared between different practical patient modelling approaches: non-OMAR, non-OMAR with manual density overrides, OMAR, and OMAR with manual density overrides.
Results: In the Gammex Phantom scans, there was no significant difference in OMAR efficacy, or effect on resulting dose distribution, for different clinical scan protocols. Tissue inserts positioned closer to metallic inserts resulted in increased residual artifacts. Despite residual artifacts, minimal range changes were observed for proton beams traveling adjacent to metal inserts for OMAR corrected images when compared to images with no metal insert. Patient CT simulations showed significant residual artifacts with meaningful effects on proton dose distributions. In all sites, OMAR with additional manual density overrides was the preferred modelling approach. To enable a review of each clinical OMAR scan, a RayStation script was developed to generate a new CT image series which consists of a difference map between the non-OMAR and OMAR scans.
Conclusion: The Philips OMAR algorithm is used routinely for proton radiotherapy CT simulations. Prior to treatment planning and target delineation, we adopt a case-by-case review and frequently perform additional manual density overrides on diminished, but residual, artifacts.
Keywords
Protons, CT, Treatment Planning
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