Abstract
Philips Healthcare released a novel metal artifact reduction algorithm for large orthopedic implants (O‐MAR). Little information was available about its CT number accuracy. Since CT numbers are used for tissue heterogeneity corrections in external beam radiotherapy treatment planning, we performed a phantom study to assess the CT number accuracy of O‐MAR. Two situations were simulated: a patient with a unilateral metallic hip prosthesis and a patient with bilateral metallic hip prostheses. We compared the CT numbers in the O‐MAR reconstructions of the simulations to those in the nonO‐MAR reconstruction and to those in a metal‐free baseline reconstruction. In both simulations, the CT number accuracy of the O‐MAR reconstruction was better than the CT number accuracy of the nonO‐MAR reconstruction. In the O‐MAR reconstruction of the unilateral simulation, all CT numbers were accurate within ±5HU (AAPM criterion). In the O‐MAR reconstruction of the bilateral simulation, CT numbers were found that differed more than ±5HU from the metal‐free baseline values. However, none of these differences were clinically relevant.PACS numbers: 87.57.Q‐, 87.57.cp
Highlights
In external beam radiotherapy treatment planning, CT numbers are used to perform tissue heterogeneity corrections.[1,2] When large metal objects are present in a CT study, which is the case for patients with pelvic malignancies and metallic hip prostheses, the CT numbers become corrupted by metal artifacts
The mean CT numbers and corresponding standard deviations in the O-MAR reconstruction were in closer agreement with the baseline values than those in the nonO-MAR reconstruction
We simulated a patient with a unilateral metallic hip prosthesis, as well as a patient with bilateral metallic hip prostheses
Summary
In external beam radiotherapy treatment planning, CT numbers are used to perform tissue heterogeneity corrections.[1,2] When large metal objects are present in a CT study, which is the case for patients with pelvic malignancies and metallic hip prostheses, the CT numbers become corrupted by metal artifacts. In 2012, Philips Healthcare (Cleveland, OH) released a novel metal artifact reduction algorithm for large orthopedic implants (O-MAR).(3) The commercial documentation clearly shows how O-MAR improves the image quality by reducing the metal artifacts. We assess the CT number accuracy of O-MAR using a phantom study. We simulated two situations: a patient with a unilateral metallic hip prosthesis and a patient with bilateral metallic hip prostheses. We compared the CT numbers in the O-MAR reconstructions of these simulations to those in the nonO-MAR reconstructions and to those in a metal-free baseline reconstruction
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