In-air calibration of new high dose rate 60Co brachytherapy sources: results of measurements on a GZP6 brachytherapy afterloading unit

SummaryBackgroundThe air kerma rate of brachytherapy sources should be determined accurately by the manufacturer and medical physicists before clinical use.AimIn the current study the air kerma rate of three new 60Co high dose rate (HDR) brachytherapy sources was obtained by in-air measurements and a Farmer type ionization chamber.Materials/MethodsThree 60Co sources of a brachytherapy afterloading unit, GZP6, were calibrated in free air using a Farmer type chamber which was calibrated in terms of air kerma in an external teletherapy 60Co beam. Several correction factors including scatter correction and non-uniformity correction factors were derived and used for in-air calibrations.ResultsThe measured air kerma rates for all sources were in good agreement (less than 2.5%) with manufacturer-provided data, and the reliability of the air kerma rates of sources was validated for clinical application.ConclusionIn-air calibration of 60Co HDR sources can be performed using a Farmer type ionization chamber with acceptable accuracy. However, accurate distance measurement and reproducible measurement setup are required.