Calibration of megavoltage cone-beam CT for radiotherapy dose calculations: Correction of cupping artifacts and conversion of CT numbers to electron density

Petit, Steven F; Elmpt, Wouter J. C. van; Lambin, Philippe

doi:10.1118/1.2836945

Title: Calibration of megavoltage cone-beam CT for radiotherapy dose calculations: Correction of cupping artifacts and conversion of CT numbers to electron density

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Abstract

Megavoltage cone-beam CT (MV CBCT) is used for three-dimensional imaging of the patient anatomy on the treatment table prior to or just after radiotherapy treatment. To use MV CBCT images for radiotherapy dose calculation purposes, reliable electron density (ED) distributions are needed. Patient scatter, beam hardening and softening effects result in cupping artifacts in MV CBCT images and distort the CT number to ED conversion. A method based on transmission images is presented to correct for these effects without using prior knowledge of the object's geometry. The scatter distribution originating from the patient is calculated with pencil beam scatter kernels that are fitted based on transmission measurements. The radiological thickness is extracted from the scatter subtracted transmission images and is then converted to the primary transmission used in the cone-beam reconstruction. These corrections are performed in an iterative manner, without using prior knowledge regarding the geometry and composition of the object. The method was tested using various homogeneous and inhomogeneous phantoms with varying shapes and compositions, including a phantom with different electron density inserts, phantoms with large density variations, and an anthropomorphic head phantom. For all phantoms, the cupping artifact was substantially removed from the images and a linear relationmore »« less

Authors:: Petit, Steven F; Elmpt, Wouter J. C. van; Lambin, Philippe

Publication Date:: Sat Mar 15 00:00:00 EDT 2008

OSTI Identifier:: 21036183

Resource Type:: Journal Article

Journal Name:: Medical Physics

Additional Journal Information:: Journal Volume: 35; Journal Issue: 3; Other Information: DOI: 10.1118/1.2836945; (c) 2008 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405

Country of Publication:: United States

Language:: English

Subject:: 62 RADIOLOGY AND NUCLEAR MEDICINE; ACCURACY; ANATOMY; CALIBRATION; COMPUTERIZED TOMOGRAPHY; CORRECTIONS; DOSIMETRY; ELECTRON DENSITY; ERRORS; IMAGE PROCESSING; IMAGES; ITERATIVE METHODS; PATIENTS; PHANTOMS; RADIATION DOSES; RADIOTHERAPY

Citation Formats


                    Petit, Steven F, Elmpt, Wouter J. C. van, Nijsten, Sebastiaan M. J. J. G., Lambin, Philippe, and Dekker, Andre L. A. J. Calibration of megavoltage cone-beam CT for radiotherapy dose calculations: Correction of cupping artifacts and conversion of CT numbers to electron density.  United States: N. p., 2008. 
        Web.  doi:10.1118/1.2836945.

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                    Petit, Steven F, Elmpt, Wouter J. C. van, Nijsten, Sebastiaan M. J. J. G., Lambin, Philippe, & Dekker, Andre L. A. J. Calibration of megavoltage cone-beam CT for radiotherapy dose calculations: Correction of cupping artifacts and conversion of CT numbers to electron density.  United States.  https://doi.org/10.1118/1.2836945

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                    Petit, Steven F, Elmpt, Wouter J. C. van, Nijsten, Sebastiaan M. J. J. G., Lambin, Philippe, and Dekker, Andre L. A. J. 2008.  
        "Calibration of megavoltage cone-beam CT for radiotherapy dose calculations: Correction of cupping artifacts and conversion of CT numbers to electron density".  United States.  https://doi.org/10.1118/1.2836945.

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@article{osti_21036183,

  title        = {Calibration of megavoltage cone-beam CT for radiotherapy dose calculations: Correction of cupping artifacts and conversion of CT numbers to electron density},

  author       = {Petit, Steven F and Elmpt, Wouter J. C. van and Nijsten, Sebastiaan M. J. J. G. and Lambin, Philippe and Dekker, Andre L. A. J.},

  abstractNote = {Megavoltage cone-beam CT (MV CBCT) is used for three-dimensional imaging of the patient anatomy on the treatment table prior to or just after radiotherapy treatment. To use MV CBCT images for radiotherapy dose calculation purposes, reliable electron density (ED) distributions are needed. Patient scatter, beam hardening and softening effects result in cupping artifacts in MV CBCT images and distort the CT number to ED conversion. A method based on transmission images is presented to correct for these effects without using prior knowledge of the object's geometry. The scatter distribution originating from the patient is calculated with pencil beam scatter kernels that are fitted based on transmission measurements. The radiological thickness is extracted from the scatter subtracted transmission images and is then converted to the primary transmission used in the cone-beam reconstruction. These corrections are performed in an iterative manner, without using prior knowledge regarding the geometry and composition of the object. The method was tested using various homogeneous and inhomogeneous phantoms with varying shapes and compositions, including a phantom with different electron density inserts, phantoms with large density variations, and an anthropomorphic head phantom. For all phantoms, the cupping artifact was substantially removed from the images and a linear relation between the CT number and electron density was found. After correction the deviations in reconstructed ED from the true values were reduced from up to 0.30 ED units to 0.03 for the majority of the phantoms; the residual difference is equal to the amount of noise in the images. The ED distributions were evaluated in terms of absolute dose calculation accuracy for homogeneous cylinders of different size; errors decreased from 7% to below 1% in the center of the objects for the uncorrected and corrected images, respectively, and maximum differences were reduced from 17% to 2%, respectively. The presented method corrects the MV CBCT images for cupping artifacts and extracts reliable ED information of objects with varying geometries and composition, making these corrected MV CBCT images suitable for accurate dose calculation purposes.},

  doi          = {10.1118/1.2836945},

  url          = {https://www.osti.gov/biblio/21036183},
  journal      = {Medical Physics},

  issn         = {0094-2405},

  number       = 3,

  volume       = 35,

  place        = {United States},

  year         = {Sat Mar 15 00:00:00 EDT 2008},

  month        = {Sat Mar 15 00:00:00 EDT 2008}

}

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