Abstract
PurposeWe investigated the impact on computed tomography (CT) image quality and photon, electron, and proton head‐and‐neck (H&N) radiotherapy (RT) dose calculations of three CT metal artifact reduction (MAR) approaches: A CT‐based algorithm (oMAR Philips Healthcare), manual water override, and our recently presented, Magnetic Resonance (MR)‐based kerMAR algorithm. We considered the following three hypotheses: I: Manual water override improves MAR over the CT‐ and MR‐based alternatives; II: The automatic algorithms (oMAR and kerMAR) improve MAR over the uncorrected CT; III: kerMAR improves MAR over oMAR.MethodsWe included a veal shank phantom with/without six metal inserts and nine H&N RT patients with dental implants. We quantified the MAR capabilities by the reduction of outliers in the CT value distribution in regions of interest, and the change in particle range and photon depth at maximum dose.ResultsWater override provided apparent image improvements in the soft tissue region but insignificantly or negatively influenced the dose calculations. We however found significant improvements in image quality and particle range impact, compared to the uncorrected CT, when using oMAR and kerMAR. kerMAR in turn provided superior improvements in terms of high intensity streak suppression compared to oMAR, again with associated impacts on the particle range estimates. ConclusionWe found no benefits of the water override compared to the rest, and tentatively reject hypothesis I. We however found improvements in the automatic algorithms, and thus support for hypothesis II, and found the MR‐based kerMAR to improve upon oMAR, supporting hypothesis III.
Highlights
AND PURPOSEMetal implants in patients scanned with x-ray computed tomography (CT) lead to potentially severe cupping and streak artifacts, as the model relating the reconstructed attenuation coefficients to the x-ray measurements breaks down
Such image corruption may be critical to the accuracy of the electron density and relative stopping power (RSP) estimates needed for external beam radiotherapy (RT) dose calculations
Based on phantom and head-and-neck patients, we investigated the impact of three different metal artifact reduction (MAR) strategies in terms of image quality and dosimetric impact for photon, electron and proton beams
Summary
Metal implants in patients scanned with x-ray computed tomography (CT) lead to potentially severe cupping and streak artifacts, as the model relating the reconstructed attenuation coefficients to the x-ray measurements breaks down. Such image corruption may be critical to the accuracy of the electron density and relative stopping power (RSP) estimates needed for external beam radiotherapy (RT) dose calculations. On the other hand, here electrons and protons, the RSP is highly sensitive to tissue variations and the plans typically contain only 1–3 beams.[1,3,4,5] The resulting dose uncertainties in electron and (the increasingly used) proton therapy can be a major concern for head-and-neck (H&N) RT patients with tumors simultaneously close to critical organs at risk (OARs) and the frequently corrupted oral region; it decreases the degrees of freedom during dose planning.[5,6]
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