Monte Carlo determination of k _Q and k _Qmsr values for the exradin A26 ionisation chamber for the Varian TrueBeam

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiotherapy Physics

Background:

• Accurate dosimetry is critical for effective radiotherapy.
• Ionisation chambers are standard tools for measuring absorbed dose.
• Conversion factors (k Q) and machine-specific factors (k Qmsr) are essential for precise dose calibration.

Purpose of the Study:

• To calculate beam quality conversion factors (k Q) for the A26 ionisation chamber.
• To determine machine-specific reference beam quality factors (k Qmsr) for the Varian TrueBeam accelerator.
• To validate simulation methods using the A12 ionisation chamber against literature values.

Main Methods:

• Monte Carlo simulations using the egs_chamber code.
• Modeling of A26 and A12 ionisation chambers based on manufacturer data.
• Utilized Varian TrueBeam phase space files and tabulated spectra (4-25 MV).

Main Results:

• Simulated A12 k Q values agreed with literature (<0.1% variation).
• A26 k Q values matched manufacturer data (within 0.5%).
• Calculated k Qmsr values for the A26 chamber were close to unity (within 0.006).

Conclusions:

• The Monte Carlo simulation methodology is accurate for determining k Q and k Qmsr.
• The calculated conversion factors for the A26 chamber are reliable for use with the Varian TrueBeam.
• The study provides accurate dosimetry data for radiotherapy applications.