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Photon extremity absorbed dose and kerma conversion coefficients for calibration geometries
1Y-12 National Security Complex, P.O. Box 2009, M.S. 8105, Oak Ridge, TN 37831-8105, USA. veinotkg@y12.doe.gov
Health Physics
|January 16, 2007
Summary
This study reveals that standard conversion coefficients for extremity dosimetry may overestimate absorbed dose, particularly for higher energy photons. New calculations provide more accurate absorbed dose values for finger and wrist phantoms in radiation protection.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Occupational Health
Background:
- Personnel dosimetry programs rely on conversion coefficients for monitoring operational quantities.
- Accurate absorbed dose assessment for extremities is crucial for individuals handling radioactive materials.
- Existing calibration geometries and phantoms (HPS N13.32) are used for extremity dosimetry.
Purpose of the Study:
- To calculate photon conversion coefficients for extremity calibration geometries.
- To determine absorbed dose and kerma conversion coefficients using Monte Carlo techniques.
- To compare calculated values with existing standards and assess potential overestimations.
Main Methods:
- Utilized Monte Carlo simulations to calculate photon conversion coefficients.
- Employed finger and wrist/arm phantoms as described in HPS N13.32.
- Calculated coefficients as a function of photon energy for specific calibration geometries.
Main Results:
- Calculated kerma values align well with existing HPS N13.32 data.
- Absorbed dose values show significant differences at higher photon energies due to unmet charged particle equilibrium.
- Existing coefficients for Cs and Co sources overestimate extremity absorbed dose.
Conclusions:
- Standard conversion coefficients in HPS N13.32 can lead to substantial overestimation of absorbed dose to extremities.
- New photon conversion coefficients are necessary for accurate extremity dosimetry.
- Overestimation can reach 62% for finger and 55% for wrist phantoms with Cs sources.
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