Measurement of absorbed dose with a bone-equivalent extrapolation chamber

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Biophysical Modeling

Background:

• Accurate absorbed dose determination is crucial for radiation therapy planning.
• Bone presents unique challenges for dosimetry due to its heterogeneous composition.
• Existing dosimetry methods may not fully account for bone's properties.

Purpose of the Study:

• To develop and validate a hybrid phantom-embedded extrapolation chamber (PEEC) for absorbed dose measurement in bone-equivalent phantoms.
• To assess the impact of chamber design and materials on dose determination accuracy.
• To establish a reliable method for dosimetry in bone for clinical radiation beams.

Main Methods:

• Utilized a hybrid PEEC constructed from Solid Water and bone-equivalent materials.
• Employed Spencer-Attix cavity theory with ionization gradient and capacitance measurements.
• Applied correction factors for scatter deficit and electrode composition, calculated using Monte Carlo techniques.
• Validated measurements with different electrode materials (graphite, steel, brass).

Main Results:

• The hybrid PEEC, with appropriate corrections, can measure absorbed dose in bone material to within 2% for high-energy photon and electron beams.
• Scatter deficit in the hybrid chamber reduced cavity dose by 0.7% to 2%.
• Graphite electrodes decreased cavity dose by up to 5% in bone-equivalent PEEC measurements.

Conclusions:

• The hybrid PEEC is a viable tool for accurate absorbed dose determination in bone-equivalent phantoms.
• Monte Carlo-derived correction factors are essential for precise dosimetry with hybrid chambers.
• This method enhances the reliability of dose delivery in radiation oncology involving bone tissues.