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Verification of CT number to density conversion for a simulator-T attachment
Australasian Physical & Engineering Sciences in Medicine
|September 11, 2002
Summary
Accurate radiotherapy planning requires precise CT number to density conversion. This study found a consistent offset in Scanvision simulator-CT air calibration, necessitating a unique calibration line for accurate density conversion.
Area of Science:
- Medical Physics
- Radiotherapy Technology
- Imaging Science
Background:
- Simulator-CT scanners like Scanvision are crucial for radiotherapy treatment planning.
- Accurate conversion of CT numbers to electron density is essential for dose calculation.
- Conventional CT scanners have established CT number to density relationships.
Purpose of the Study:
- To calculate and verify a CT number to density conversion table for the Scanvision simulator-CT.
- To assess the accuracy of CT number measurements for radiotherapy applications.
- To determine if a standard calibration line is applicable or if a specific one is needed.
Main Methods:
- Calculated CT number to density conversion using polyethylene and air normalization.
- Verified the reproducibility of CT number measurements with the simulator-CT.
- Compared the simulator-CT's calibration with conventional CT scanner data.
Main Results:
- The linear fit for CT number to density was similar to conventional scanners.
- A significant offset was observed for air (approx. 178 HU with polyethylene, 262 HU with air normalization).
- This offset extended to other low-density samples, indicating a systematic difference.
Conclusions:
- The Scanvision simulator-CT reproducibly measures CT numbers.
- A unique calibration line is required for accurate CT number to density conversion in radiotherapy planning.
- Implementing a specific calibration line ensures accurate electron density determination for improved treatment planning.