Establishment of air kerma reference standard for low dose rate Cs-137 brachytherapy sources

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A guarded cylindrical graphite ionization chamber of nominal volume Symbol was designed and fabricated for use as a reference standard for low-dose rate Symbol brachytherapy sources. The air kerma calibration coefficient Symbol of this ionization chamber was estimated analytically using Burlin's general cavity theory, as well as by the Monte Carlo simulation and validated experimentally using Amersham CDCS-J-type Symbol reference source. In the analytical method, the Symbol was calculated for 662 keV gamma rays of Symbol brachytherapy source. In the Monte Carlo method, the geometry of the measurement setup and physics-related input data of the Symbol source and the surrounding material were simulated using the Monte Carlo N-Particle code. The photon energy fluence was used to arrive at the reference air kerma rate (RAKR) using mass energy absorption coefficient. The energy deposition rates were used to simulate the value of charge rate in the ionization chamber, and the Symbol was determined. The analytical and Monte Carlo values of Symbol of the cylindrical graphite ionization chamber for Symbol brachytherapy source are in agreement within 1.07%. The deviation of analytical and Monte Carlo values from experimental values of Symbol is 0.36% and 0.72%, respectively. This agreement validates the analytical value, and establishes this chamber as a reference standard for RAKR or AKS measurement of Symbol brachytherapy sources.

PACS numbers: 87.53.Bn, 87.53.Jw,, 87.55.Qr

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