A simplified analytical approach to estimate the parameters required for strength determination of HDR Ir-192 brachytherapy sources using a Farmer-type ionization chamber

作者：Kumar Sudhir; Srinivasan P; Sharma S D^*; Mayya Y S

来源：Applied Radiation and Isotopes, 2012, 70(1): 282-289.

DOI：10.1016/j.apradiso.2011.08.009

• Brachytherapy
• Analytical approach
• Farmer-type ionization chamber
• HDR Ir-192 source
• Monte Carlo

Measuring the strength of high dose rate (HDR) Ir-192 brachytherapy sources on receipt from the vendor is an important component of a quality assurance program. Owing to their ready availability in radiotherapy departments, the Farmer-type ionization chambers are also used to determine the strength of HDR Ir-192 brachytherapy sources. The use of a Farmer-type ionization chamber requires the estimation of the scatter correction factor along with positioning error (c) and the constant of proportionality (f) to determine the strength of HDR Ir-192 brachytherapy sources. A simplified approach based on a least squares method was developed for estimating the values of f and M-s. The seven distance method was followed to record the ionization chamber readings for parameterization of f and M-s. Analytically calculated values of M-s were used to determine the room scatter correction factor (K-sc). The Monte Carlo simulations were also carried out to calculate f and K-sc to verify the magnitude of the parameters determined by the proposed analytical approach. The value of f determined using the simplified analytical approach was found to be in excellent agreement with the Monte Carlo simulated value (within 0.7%). Analytically derived values of K-sc were also found to be in good agreement with the Monte Carlo calculated values (within 1.47%). Being far simpler than the presently available methods of evaluating f, the proposed analytical approach can be adopted for routine use by clinical medical physicists to estimate f by hand calculations.

• 出版日期2012-1