MRI-based computed tomography metal artifact correction method for improving proton range calculation accuracy.
OBJECTIVE
Computed tomography (CT) artifacts can severely degrade dose calculation accuracy in proton therapy. Prompted by the recently increased popularity of magnetic resonance imaging (MRI) in the radiation therapy clinic, we developed an MRI-based CT artifact correction method for improving the accuracy of proton range calculations.


METHODS
The proposed method replaces corrupted CT data by mapping CT Hounsfield units (HU number) from a nearby artifact-free slice, using a coregistered MRI. MRI and CT volumetric images were registered with use of 3-dimensional (3D) deformable image registration (DIR). The registration was fine-tuned on a slice-by-slice basis by using 2D DIR. Based on the intensity of paired MRI pixel values and HU from an artifact-free slice, we performed a comprehensive analysis to predict the correct HU for the corrupted region. For a proof-of-concept validation, metal artifacts were simulated on a reference data set. Proton range was calculated using reference, artifactual, and corrected images to quantify the reduction in proton range error. The correction method was applied to 4 unique clinical cases.


RESULTS
The correction method resulted in substantial artifact reduction, both quantitatively and qualitatively. On respective simulated brain and head and neck CT images, the mean error was reduced from 495 and 370 HU to 108 and 92 HU after correction. Correspondingly, the absolute mean proton range errors of 2.4 cm and 1.7 cm were reduced to less than 2 mm in both cases.


CONCLUSIONS
Our MRI-based CT artifact correction method can improve CT image quality and proton range calculation accuracy for patients with severe CT artifacts.
Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas.
Peter C
PC
Park
Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia.
Eduard
E
Schreibmann
Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia.
Justin
J
Roper
Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia.
Eric
E
Elder
Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia.
Ian
I
Crocker
Varian Medical Systems, Palo Alto, California.
Tim
T
Fox
Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas.
X Ronald
XR
Zhu
Scripps Proton Therapy Center, San Diego, California.
Lei
L
Dong
Department of Radiation Oncology, Winship Cancer Institute of Emory University, Atlanta, Georgia. Electronic address: anees.dhabaan@emory.edu.
Anees
A
Dhabaan
D016477:Artifacts; D001921:Brain / Q000000981:diagnostic imaging / Q000473:pathology; D003793:Dental Restoration, Permanent; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008670:Metals; D019047:Phantoms, Imaging; D011522:Protons; D011856:Radiographic Image Enhancement / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013525:Surgical Instruments; D014057:Tomography, X-Ray Computed / Q000379:methods*
D008670:Metals; D011522:Protons