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

Document Type : Original Paper

Authors

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

Abstract

With the computerized treatment planning system the dosimetrist or medical physicist makes the plan and acquires the dose distribution calculation with heterogeneity correction. CT calculates the positions and densities of the patient's organs using pixels as a coordinate system, the degree of radiation attenuation in the organ is described as a unit called a CT number or a Hounsfield Unit (HU) per pixel. The treatment planning system (TPS) algorithm converts the CT no. to relative electron density to calculate the dose distribution. There is a need to measure the conversion relationship between the CT number and RED and then transfer it to the radiotherapy TPS for dose calculation accuracy. This process is a very important step in commissioning a CT simulator. This study was carried out to upgrade the CTDI phantom to a density phantom by making multiple materials with different densities in the laboratory because Our department lacks a density phantom. This developed phantom gives an alternative to the standard commercial density phantom. We made 14 tissue-mimicking material plugs, their characteristics were measured, and we scanned the developed density phantom that we got by CT- simulator using the Dual Energy^DE_Direct Density protocol (120 KVp& 211 mAs and slice thickness 3mm), as this protocol will reconstruct automatically a DE-Rho series with relative electron density maps of the materials used.CT number (HU) for different density materials was obtained from CT images of the

phantom acquired. The HU-RED calibration curve was drawn from CT images

with various tissue substitutes acquired, then we saved it in the radiation TPS for dose calculations with more accuracy.The new TEMs may make the calibration procedure simpler while maintaining the precision of the stoichiometric calibration, especially for the CT-number calibration in radiation treatment planning. The developed phantom achieved our goal and saved the cost of purchase.

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Iranian Journal of Medical Physics

Articles in Press, Accepted Manuscript
Available Online from 13 March 2023

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History

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

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