Calibration coefficient of reference brachytherapy ionization chamber using analytical and Monte Carlo methods

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Nuclear Engineering

Background:

• Accurate measurement of high dose rate (HDR) (192)Ir brachytherapy sources is crucial for effective cancer treatment.
• Reference dosimeters are essential for calibrating radiation sources and ensuring treatment accuracy.
• Existing methods for calibrating HDR sources require precise and reliable dosimetric tools.

Purpose of the Study:

• To design and fabricate a cylindrical graphite ionization chamber for use as a reference dosimeter.
• To determine the air kerma calibration coefficient (N(K)) of the fabricated ionization chamber using analytical and Monte Carlo methods.
• To experimentally validate the performance of the ionization chamber by measuring the reference air kerma rate (RAKR) of HDR (192)Ir sources.

Main Methods:

• A 1002.4 cm(3) cylindrical graphite ionization chamber was designed and fabricated at Bhabha Atomic Research Centre (BARC).
• Analytical estimation of N(K) using Burlin general cavity theory, calculating coefficients for each spectral line of an HDR (192)Ir source.
• Monte Carlo simulation using the Monte Carlo N-particle code to model the measurement setup, HDR (192)Ir source, and surrounding materials.

Main Results:

• The Monte Carlo calculated N(K) showed agreement within 1.77% compared to the analytical method.
• Experimentally determined RAKR of HDR (192)Ir sources using the reference ionization chamber agreed within 1.43% with vendor-quoted values.
• The developed ionization chamber serves as a reliable reference dosimeter for HDR (192)Ir brachytherapy sources.

Conclusions:

• The designed graphite ionization chamber is suitable for accurate dosimetry of HDR (192)Ir brachytherapy sources.
• Both analytical and Monte Carlo methods provide consistent results for the air kerma calibration coefficient.
• The experimental validation confirms the chamber's capability to measure reference air kerma rates accurately.