IC-10계열의 이온전리함과 TG-21을 이용한 장기간 선형가속기의 출력선량 평가 비교

Abstract

This study is to provided the accuracy and stability of the output dose of linear accelerator photon beams by using the IC-10 and IC-15 air ionization chambers through the Task Group 21 protocol. The gas absorbed dose calibration factor Ngas is determined by using the Bragg-Gray cavity theory for the air exposure calibration factor Nx of Co-60 gamma rays which is delivered from manufacture through NBS calibration. The ionization chamber of IC-10 series composit the Shonka C-552 material with density 1.76 g/ml which is equivalent to air material. the authors provided the Awall from correction equation for air absorbed calibration factor Ngas and ion recombination correction factor Aion from Pion analytic measurement. The absorbed dose in water phantorm is derived from the Ngas including the correction factors mass stopping power ratio of water to that of gas, ion recombination and replacement for 6 and 23 MV X rays, respectively. The determined absorbed dose of water phantom exposed to a postal TLD block for output evaluation in MDACC’s postal monitoring program. The results of comparisons of evaluated absorbed dose to that of MDACC have shown the 1.000 ± 0.012 for 6 MV and 1.001 0.013 discrepancy for 23 MV X rays for a long term followed. This study shows the evaluated outputs for linear accelerator photon beams are very close to that of international output monitor with small discrepancy of 1.3% for one and half decade.