The Measurement of the Air-Kerma Rate in Air and a Solid Phantom with Ionization Chambers for a 192Ir HDR Brachytherapy Source

Introduction: This study aims to measure the air-kerma rate of 192-Ir-HDR-afterloading source with an ionization chamber in air and a solid cylindrical phantom separately and to compare the dose calibration by the American Association of Physicists in Medicine (AAPM) Task Group TG-43U1 formalism with the Abacus treatment planning system (TPS). Materials and Methods: The air-kerma rate of Ir-192 source was measured by an ionization chamber in air and a solid cylindrical phantom separately. For the interesting point position P (8cm, 90 degrees), the values of the dose were calculated with the TG-43U1 formula and compared with data from the Abacus TPS with single and multiple dwell positions, respectively. Results: The air-kerma rate percentage deviations between the detector measurements in air and the source certificate were -1.28%, -0.91%, -0.71%, and 0.33% at the distances of 25cm, 50cm, 75cm, and 100cm, respectively. For the measurement in solid cylindrical phantom, the percent deviation from the air-kerma rate certificate was 1.85%. The percentage deviations of the dose calibration between Abacus TPS and TG-43U1 formalism at P (8cm, 90 degrees) were -2.30%, 1.76%, and 2.10% with different distances (between the dwell positions) of 0cm, 0.5cm, and 1cm, respectively. Conclusion: The in-air technique was a new attempt for clinic routine measurement. Further studies are still necessary. As a treatment planning system, the Abacus TPS should apply the AAPM TG-43U1 formulism for the development required in the future.