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Corrected relationship between %dd(10)x and stopping-power ratios.
1Ionizing Radiation Standards, Institute for National Measurement Standards, National Research Council of Canada, Ottawa, Ontario.
Medical Physics
|May 5, 1999
Summary
A corrected linear equation refines the relationship between the Spencer-Attix water/air stopping power ratio and photon depth-dose percentage. This improves accuracy in calculating kQ factors for absorbed-dose calibration in radiotherapy.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Radiotherapy Physics
Background:
- The Spencer-Attix water/air stopping power ratio is crucial for radiotherapy dosimetry.
- A previous linear relationship with %dd(10)x was used for calculating kQ factors.
- An error in the original formulation by Kosunen and Rogers has been identified.
Purpose of the Study:
- To present a corrected linear equation for the Spencer-Attix water/air stopping power ratio.
- To provide updated %dd(10)x values for improved dosimetry calculations.
- To assess the impact of the correction on calculated kQ factors.
Main Methods:
- Re-evaluation of the relationship between the Spencer-Attix water/air stopping power ratio and %dd(10)x.
- Utilizing corrected %dd(10)x values derived from recent assessments.
- Comparison of kQ factor calculations using both original and corrected relationships.
Main Results:
- A corrected linear equation is established: (L/p)water(air)=1.275-0.00231[%dd(10)x].
- Corrected %dd(10)x values show changes up to 2%.
- The net effect on calculated kQ factors is minimal, less than 0.2%.
Conclusions:
- The corrected relationship ensures greater accuracy in radiotherapy dosimetry.
- The small impact on kQ factors indicates the robustness of the dosimetry protocols.
- This work refines fundamental parameters used in absorbed-dose calibration.