Iranian Journal of Medical Physics

Iranian Journal of Medical Physics

Upgrading a Computed Tomography Dose Index (CTDI) Phantom to an Electron Density (ED) Phantom for Commissioning a CT Simulator

Document Type : Original Paper

Authors
Rehab Abd Elaziz 1
alia ahmed 2
ebrahim awad 3
Mohamed osama 4
Ahmed oraby 5
1 Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt.
2 Clinical Oncology &Nuclear Medicine Dept., Faculty of Medicine, Mansoura University, Mansoura, Egypt.
3 Clinical Oncology and Nuclear Medicine Department, Faculty of Medicine, Mansoura University, Egypt
4 biomedical engineering , faculty of engineering, Helwan university
5 Physics Department, Faculty of Science, Mansoura University, Mansoura, Egypt
10.22038/ijmp.2023.68799.2206
Abstract
Introduction: A crucial step in commissioning a CT simulator is measuring the conversion relationship between the CT number and Relative Electron Density (RED) and transferring it to the radiotherapy TPS for accurate dose calculation.
Material and Methods: In order to automatically reconstruct a DE-Rho series with relative electron density maps of the materials used, 14 tissue-mimicking material plugs were made, their properties were measured, and the developed density phantom was scanned by CT-simulator using the Dual Energy^DE_Direct Density protocol.
Results: CT numbers (HU) for various densities of materials were determined. Utilizing the resultant HU from CT scans, the relative electron density, or RED, was computed. The HU-RED calibration curve was created using CT scans that were obtained with different tissue replacements.
Conclusion: Particularly for the CT-number calibration in radiation therapy planning, the new Tissue Equivalent Materials (TEMs) may simplify the calibration process without sacrificing the accuracy of the stoichiometric calibration. Our objective was met and the purchase cost was avoided thanks to the developed phantom.
Keywords
Radiotherapy
Treatment Planning System
Computed Tomography
Calibration Curve
Density Phantom
Relative Electron Density
Subjects
  1. International Atomic Energy Agency (IAEA). Commissioning and Quality Assurance of Computerized Planning Systems for Radiation Treatment of Cancer. TECHNICAL REPORTS SERIES NO. 430, Vienna, Austria. 2004
  2. Hyun Joon An, Jaeman Son, Hyeongmin Jin, Jiwon Sung, Minsoo Chun. Acceptance Test and Clinical Commissioning of CT Simulator. Progress in Medical Physics. 2019. J 30 (4): 160-6.
  3. American Association of Physicists in Medicine (AAPM): Benedick Fraass, Karen Doppke, Margie Hunt, Gerald Kutcher, George Starkschall, Robin Stern, and Jake Van Dyke, Radiation Therapy Committee Task Group 53. Quality Assurance for Clinical Radiotherapy Treatment Planning. Medical Physics. 1998. J 25 (10): 1773-829.
  4. International Atomic Energy Agency (IAEA). Commissioning of Radiotherapy Treatment Planning Systems: Testing for Typical External Beam Treatment Techniques. TEC DOC-1583. 2008.
  5. Advanced Electron Density Phantom. Available from: https://www.cirsinc.com/products/radiation-therapy/electron-density-phantom/)
  6. International Commission on Radiation Units and Measurement (ICRU). Tissue Substitutes in Radiation Dosimetry and Measurement. Report No. 44 (Bethesda, MD: ICRU). 1988.
  7. Loevinger R, Budinger TF, Watson EE. Medical Internal Radiation Dosimetry (MIRD) Primer for Absorbed Dose Calculations. 1988
  8. International Commission on Radiation Units and Measurement (ICRU). Photon, electron, proton, and neutron interaction data for body tissues. Report No. 46 (Bethesda, MD: ICRU). 1992.
  9. Mahmoudi R, Jabbari N, Aghdasi M, Khalkhali HR. Energy dependence of measured CT numbers on substituted materials used for CT number calibration of radiotherapy treatment planning systems. PLoS One. 2016 Jul 8;11(7):e0158828.
  10. Simon Jonathan Thomas. Relative electron density calibration of CT scanners for radiotherapy treatment planning. The British J of Radiology. 1999.72: 781-6.
  11. Zhu J, Penfold SN. Dosimetric comparison of stopping power calibration with dual‐energy CT and single‐energy CT in proton therapy treatment planning. Medical physics. 2016 Jun;43(6Part1):2845-54.
  12. International Atomic Energy Agency (IAEA). Quality Assurance Programme for Computed Tomography: Diagnostic and Therapy Applications. IAEA HUMAN HEALTH SERIES 19. 2012.
  13. Afifi MB, Abdelrazek A, Deiab NA, Abd El-Hafez AI, El-Farrash AH. The effects of CT x-ray tube voltage and current variations on the relative electron density (RED) and CT number conversion curves. Journal of Radiation Research and Applied Sciences. 2020 Jan 1;13(1):1-1.
  14. Davis AT, Palmer AL, Nisbet A. Can CT scan protocols used for radiotherapy treatment planning be adjusted to optimize image quality and patient dose? A systematic review. The British journal of radiology. 2017 Aug 1;90(1076):20160406.
  15. Yohannes I, Kolditz D, Langner O, Kalender WA. A formulation of tissue-and water-equivalent materials using the stoichiometric analysis method for CT-number calibration in radiotherapy treatment planning. Physics in Medicine & Biology. 2012 Feb 14;57(5):1173.
  16. Skaug Sande EP, Catrine Trægde Martinsen A, Olaug Hole E, Olerud HM. Interphantom and interscanner variations for Hounsfield units—establishment of reference values for HU in a commercial QA phantom. Physics in Medicine and Biology. 2010 Sep;55(17):5123-35.
  17. Coolens C and Childs P J “Calibration of CT Hounsfield units for radiotherapy treatment planning of patients with metallic hip prostheses: the use of the extended CT-scale”. Physics in Medicine and Biology J 2003 (48). 1591–
  18. Bustillo JP, Tumlos R, Remoto RZ. Intensity modulated radiotherapy (IMRT) phantom fabrication using fused deposition modeling (FDM) 3D printing technique. InWorld Congress on Medical Physics and Biomedical Engineering. 2018;3:509-15.
  19. Rafic M, Ravindran P. Evaluation of on-board imager cone beam CT hounsfield units for treatment planning using rigid image registration. Journal of Cancer Research and Therapeutics. 2015 Oct 1;11(4):690-6.
  20. Young HM, Park CK, Chau OW, Lee TY, Gaede S. Volumetric computed tomography for radiotherapy simulation and treatment planning. Journal of Applied Clinical Medical Physics. 2021 Aug;22(8):295-302.
  21. Gao L, Sun H, Ni X, Fang M, Lin T. Effects of 16-bit CT imaging scanning conditions for metal implants on radiotherapy dose distribution. Oncology letters. 2018 Feb 1;15(2):2373-9.
Iranian Journal of Medical Physics
Volume 21, Issue 3 - Serial Number 3
May and June 2024
Pages 154-159

  • Receive Date 04 November 2022
  • Revise Date 02 March 2023
  • Accept Date 13 March 2023