Practical dosimetry procedure of air kerma for kilovoltage X-ray imaging in radiation oncology using a 0.6-cc cylindrical ionization chamber with a cobalt absorbed dose-to-water calibration coefficient.

In this study, we implemented a practical dosimetry procedure of air kerma for kilovoltage X-ray beams using a 0.6-cc cylindrical ionization chamber, and validated the procedure with the accuracy of the measurements using the 0.6-cc chamber compared to the measurements using a 6-cc chamber and a semiconductor device. In addition, the kerma area products (KAPs) were compared with the dose reference levels of radiology. A modified air kerma formalism using a 0.6-cc cylindrical ionization chamber air kerma formalism with a cobalt absorbed dose-to-water calibration coefficient was implemented. Validation of the formalism showed good agreement between the 0.6-cc chamber and the 6-cc chamber (< 5%), and between the 0.6-cc chamber and the semiconductor device (< 2%) in the 60-120 kV range. The KAPs for four RO machines had difference factors of 0.04-15.4 and 0.01-4.1 from their median and maximum dose reference levels in radiology, respectively.