Beam quality corrections for parallel-plate ion chambers in electron reference dosimetry.

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Computational Physics

Background:

• Clinical electron beam dosimetry relies on parallel-plate ionization chambers as recommended by international protocols.
• Variations in chamber design can influence perturbation corrections and beam quality factors.
• Accurate beam quality correction factors are crucial for precise dose measurements.

Purpose of the Study:

• To perform detailed Monte Carlo simulations of beam quality correction factors for four types of parallel-plate ionization chambers.
• To compare simulation results with established dosimetry protocols, specifically IAEA TRS-398.
• To assess the impact of chamber design on perturbation corrections and overall dosimetry uncertainty.

Main Methods:

• Utilized detailed Monte Carlo simulations to model NACP-02, Markus, Advanced Markus, and Roos parallel-plate ionization chambers.
• Calculated beam quality correction factors, considering wall and cavity perturbation effects.
• Quantified type-B uncertainties arising from cross-sectional data, material composition, and geometry.

Main Results:

• Deviations between simulated and IAEA TRS-398 recommended beam quality corrections range from 0% to 2%, varying with electron energy and chamber type.
• Well-guarded chambers showed deviations attributed to energy-dependent wall perturbation.
• The guardless Markus chamber exhibited the largest deviations (>2%) due to compensating perturbation effects.

Conclusions:

• Monte Carlo simulations provide more accurate beam quality correction factors than current protocols for parallel-plate chambers.
• Understanding chamber-specific perturbations can significantly reduce uncertainties in clinical electron dosimetry.
• This research supports a potential reduction in the overall uncertainty of 1.7% for clinical electron dosimetry.