Three-voltage linear method to determine ion recombination in proton and light-ion beams

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Particle Beam Therapy

Background:

• Accurate ion recombination correction (k s) is crucial for precise dosimetry in particle beams.
• Existing methods for determining k s can be complex or have limitations with specific chamber types or beam conditions.

Purpose of the Study:

• To investigate and validate a new practical method, the three-voltage linear method (3VL-method), for determining the ion recombination correction factor (k s).
• To assess the applicability and accuracy of the 3VL-method for plane-parallel and Farmer-type cylindrical chambers in various particle beams.

Main Methods:

• The 3VL-method involves measuring ionization current at three voltages within a linear region to determine saturation current.
• k s is calculated by dividing the determined saturation current by the current at the operating voltage.
• Experimental data from passively scattered and scanned particle beams were compared with theoretical models (Boag, Jaffé).

Main Results:

• Excellent agreement was found between the 3VL-method and model fits for plane-parallel chambers.
• For Farmer-type chambers, a linear relationship of k s with 1/V² (continuous beams) or 1/V (pulsed beams) was observed, enabling the 3VL-method's application.
• The 3VL-method provides accurate k s determination at any polarizing voltage for the tested particle beams and chamber types (Roos, Markus, NE2571).

Conclusions:

• The 3VL-method is a simple, practical, and accurate technique for determining the ion recombination correction factor (k s) in particle dosimetry.
• This method offers advantages over existing techniques, including not requiring the operating voltage to be one of the measurement voltages and inherent linearity verification.