Exposure-to-absorbed-dose conversion for human adult cortical bone

Area of Science:

• Medical Physics
• Radiological Dosimetry
• Biomedical Engineering

Background:

• Accurate conversion of radiation exposure to absorbed dose in bone is critical for radiation protection and medical imaging.
• The f-factor, dependent on photon energy-absorption coefficients, is essential for this conversion under electron equilibrium.
• Existing methods may not fully account for bone composition variations and spectral characteristics.

Purpose of the Study:

• To calculate mass energy-absorption coefficients and f-factors for human bone across a wide photon energy range (1 keV to 1.5 MeV).
• To evaluate the impact of different bone compositions, as recommended by ICRU and ICRP, on f-factor values.
• To compare spectrum-averaged f-factors with those derived from equivalent photon energy approximations.

Main Methods:

• Utilized recommended compositions for human adult compact or cortical bone from ICRU and ICRP publications.
• Calculated mass energy-absorption coefficients and f-factors for photon energies from 1 keV to 1.5 MeV.
• Computed spectrum-averaged f-factors for calibration X-ray beams (10-250 kVp) and compared them with equivalent photon energy methods.

Main Results:

• Presented mass energy-absorption coefficients and f-factors for three human bone compositions.
• Demonstrated significant differences in f-factors at low photon energies (<200 keV) due to varying calcium content in bone.
• Showed that using an equivalent photon energy derived from half-value layer thickness provides generally poor predictions at low energies.

Conclusions:

• The study provides essential data on f-factors for accurate absorbed dose determination in bone.
• Bone composition, particularly calcium content, significantly influences f-factors at lower photon energies.
• Approximating broad energy spectra with a single equivalent photon energy is inadequate for precise dosimetry in bone at low energies.