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The elements of tissue-air ratio and systematic error
P S Nizin1, D M Bellezza, R B Mooij
1Baylor College of Medicine, Department of Radiology, Houston, Texas USA.
Medical Physics
|July 1, 1996
Summary
This study derives an analytical expression for systematic error in tissue-air ratio (TAR) calculations. A new method using linear extrapolation eliminates the need for dose conversion, enabling accurate TAR determination free from systematic errors.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Radiotherapy Physics
Background:
- Tissue-air ratio (TAR) is crucial for radiation therapy dose calculations.
- Current TAR determination methods rely on in-phantom and in-air ionization measurements.
- Systematic errors arise from difficulties in applying correction factors for dose conversion.
Purpose of the Study:
- To derive an analytical expression for systematic error in TAR calculations.
- To develop a method for determining TARs free from systematic error.
- To eliminate the need for dose conversion in TAR calculations.
Main Methods:
- Analytical derivation of systematic error in TAR.
- Utilizing linear extrapolation to obtain accurate zero-field data.
- Applying the method to 60Co gamma radiation in water for TAR generation.
Main Results:
- An analytical expression for systematic error in TAR was derived.
- A novel method eliminates the need for ionization-to-dose conversion.
- Accurate TAR data, free of systematic error, can be generated.
Conclusions:
- The derived method provides accurate tissue-air ratio (TAR) data.
- This approach simplifies TAR determination by avoiding dose conversion.
- The method shows potential for application in therapeutic X-ray beams.