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

Abstract

Background: The air kerma rate of brachytherapy sources should be determined accurately by the manufacturer and medical physicists before clinical use. Aim: In 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/methods: Three 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. Results: The 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. Conclusion: In-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.