Cone-beam CT (CBCT) images acquired during radiation
treatment can be used to recalculate the dose distribution as well as to
confirm the treatment location. However, it is difficult to obtain the electron
densities (EDs) necessary for dose calculation from CBCT images because of the
effects of scatter contamination during CBCT image acquisition. This paper
presents a mathematical method for converting the pixel values of CBCT images
(CBCT values) into Hounsfield units (HUs) of
radiation treatment simulation CT (simCT) images for use in radiation
treatment planning. CBCT values are converted into HUs by matching the
histograms of the CBCT values with the histograms of the HUs for each slice via
linear scaling of the CBCT values. For prostate cancer and head-and-neck cancer
patients, the EDs obtained from converted CBCT values (mCBCT values) show good
agreement with the EDs obtained from HUs, within approximately 3.0%, and the
dose calculated on the basis of CBCT images shows good
agreement with the dose calculated on the basis of the simCT images, within
approximately 2.0%. Because the CBCT values are converted for each slice, this
conversion method can account for variation in the CBCT values associated with
differences in body size, body shape, and inner tissue structures, as well as
in longitudinally displaced positions from the isocenter, unlike conventional
methods that use electron density phantoms. This
method improves on conventional CBCT-ED conversion and shows considerable potential for improving the accuracy of radiation treatment planning
using CBCT images.
References
[1]
Oldham, M., Letourneau, D., Watt, L., Hugo, G., Yan, D., Lockman, D., Kim, L.H., Chen, P.Y., Martinez, A. and Wong, J.W. (2005) Cone-Beam-CT Guided Radiation Therapy: A Model for On-Line Application. Radiotherapy & Oncology, 75, 271-278. https://doi.org/10.1016/j.radonc.2005.03.026
[2]
Ingrosso, G., Miceli, R., Fedele, D., Ponti, E., Benassi, M., Barbarino, R., Murro, L.D., Giudice, E., Santarelli, F. and Santoni, R. (2012) Cone-Beam Computed Tomography in Hypofractionated Stereotactic Radiotherapy for Brain Metastases. Radiation Oncology, 7, 54. http://ro-journal.biomedcentral.com/articles/10.1186/1748-717X-7-54 https://doi.org/10.1186/1748-717X-7-54
[3]
Yoo, S. and Yin, F.F. (2006) Dosimetric Feasibility of Cone-Beam CT-Based Treatment Planning Compared to CT-Based Treatment Planning. International Journal of Radiation Oncology, Biology, Physics, 66, 1553-1561. https://doi.org/10.1016/j.ijrobp.2006.08.031
[4]
Wu, Q.J., Li, T., Wu, Q. and Yin, F.F. (2011) Adaptive Radiation Therapy: Technical Components and Clinical Applications. Cancer Journal, 17, 182-189. https://doi.org/10.1097/PPO.0b013e31821da9d8
[5]
Constantinou, C. and Harrington, J.C. (1992) An Electron-Density Calibration Phantom for CT-Based Treatment Planning Computers. Medical Physics, 19, 325-327. https://doi.org/10.1118/1.596862
[6]
Thomas, S.J. (1999) Relative Electron Density Calibration of CT Scanners for Radiotherapy Treatment Planning. British Journal of Radiology, 72, 781-786. https://doi.org/10.1259/bjr.72.860.10624344
[7]
Seco, J. and Evans, P.M. (2006) Assessing the Effect of Electron Density in Photon Dose Calculations. Medical Physics, 33, 540-552. https://doi.org/10.1118/1.2161407
[8]
Hu, W., Ye, J., Wang, J., Ma, X. and Zhang, Z. (2010) Use of Kilovoltage X-Ray Volume Imaging in Patient Dose Calculation for Head-and-Neck and Partial Brain Radiation Therapy. Radiation Oncology, 5. http://www.ro-journal.com/content/5/1/29 https://doi.org/10.1186/1748-717X-5-29
[9]
Yang, Y., Schreibmann, E., Li, T., Wang, C. and Xing, L. (2007) Evaluation of On-Board kV Cone Beam CT (CBCT)-Based Dose Calculation. Physics in Medicine & Biology, 52, 685-705. https://doi.org/10.1088/0031-9155/52/3/011
[10]
Richter, A., Hu, Q., Steglich, D., Baier, K., Wilbert, J., Guckenberger, M. and Flentje, M. (2008) Investigation of the Usability of Conebeam CT Data Sets for Dose Calculation. Radiation Oncology, 3, 42. http://ro-journal.biomedcentral.com/articles/10.1186/1748-717X-3-42 https://doi.org/10.1186/1748-717X-3-42
[11]
Hatton, J., McCurdy, B. and Greer, P.B. (2009) Cone Beam Computerized Tomography: The Effect of Calibration of the Hounsfield Unit Number to Electron Density on Dose Calculation Accuracy for Adaptive Radiation Therapy. Physics in Medicine & Biology, 54, N329-N346. https://doi.org/10.1088/0031-9155/54/15/N01
[12]
Guan, H. and Dong, H. (2009) Dose Calculation Accuracy using Cone-Beam CT (CBCT) for Pelvic Adaptive Radiotherapy. Physics in Medicine & Biology, 54, 6239-6250. https://doi.org/10.1088/0031-9155/54/20/013
[13]
Rong, Y., Smilowitz, J., Tewatia, D., Tome, W.A. and Paliwal, B. (2010) Dose Calculation on kV Cone Beam CT Images: An Investigation of the HU-Density Conversion Stability and Dose Accuracy using the Site-Specipic Calibration. Medical Dosimetry, 35, 195-207.
[14]
Van Zijtvetd, M., Dirkx, M. and Heijmen, B. (2007) Correction of Cone Beam CT Values Using a Planning CT for Derivation of the “Dose of the Day”. Radiotherapy and Oncology, 85, 195-200.
[15]
Boggula, R., Lorenz, F., Abo-Madyan, Y., Lohr, F., Wolff, D., Boda-Heggemann, J., Hesser, J., Wenz, F. and Wertz, H. (2009) A New Strategy for Online Adaptive Prostate Radiotherapy Based on Cone-Beam CT. Zeitschrift für Medizinische Physik, 19, 264-276.
[16]
Fotina, I., Hopfgartner, J., Stock, M., Steininger, T., Lütgendorf-Caucig, C. and Georg, D. (2012) Feasibility of CBCT-Based Dose Calculation: Comparative Analysis of HU Adjustment Techniques. Radiotherapy and Oncology, 104, 249-256.
[17]
Marchant, T.E., Moore, C.J., Rowbottom, C.G., Mackey, R.I. and Williams, P.C. (2008) Shading Correction Algorithm for Improvement of Cone Beam CT Images in Radiotherapy. Physics in Medicine & Biology, 53, 5719-5733. https://doi.org/10.1088/0031-9155/53/20/010
[18]
Chu, J.C.H., Ni, B., Kriz, R. and Saxena, V.A. (2000) Applications of Simulator Computed Tomography Number for Photon Dose Calculations during Radiotherapy Treatment Planning. Radiotherapy and Oncology, 55, 65-73.
