Attix free-air chamber correction factors computed using EGSnrc.

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Computational Physics

Background:

• The Attix free-air chamber (FAC) is crucial for absolute air-kerma measurements of low-energy photon beams.
• Existing correction factors, established in the 1990s, require updating for new beam development.

Purpose of the Study:

• To compute monoenergetic correction factors for the Attix FAC.
• To enable the determination of correction factors for arbitrary polyenergetic beams.

Main Methods:

• A Monte Carlo model of the Attix FAC was developed using EGSnrc.
• Egs_fac and egs_chamber user codes calculated correction factors for photon beams (5-50 keV).
• Factors included aperture transmission, scatter, and electron losses.

Main Results:

• Correction factors were computed at 0.5 keV intervals.
• Newly calculated beam-specific factors closely matched existing values (within 0.1%).

Conclusions:

• A method for determining monoenergetic correction factors for free-air chambers is presented.
• Beam-specific factors can be derived from known photon spectra.
• This methodology is adaptable to other free-air chambers.