SU-E-T-36: Determination of the Beam Quality Correction Factor for the Liquid Ioinization Chamber in a Clinical Photon Beam

Abstract

Purpose: The beam quality correction factor Koo0 of microLion chamber is still unknown and should be determined for the application of the chamber to the reference dosimetry. The objective of this study is to calculate the beam quality correction factor of microLion chamber for the high energy 6MV photon beam from Clinac iX (Varian, USA) using two alternative ways; Monte Carlo simulation, in particular EGSnrc system and experimental decision. Methods: For the present work the Cobalt60 gamma beam (Theratron780) is employed as beam source in the calibration beam quality and the high energy 6MV photon beam from the Linac (Clinac iX) is selected as quality of user beam. We have employed the egs cavity code, the EGSnrc user code, to model microLion chamber. Results: The correction factor of the PTW30013 chamber is given 0.995 for the photon beam quality TPR20,10 of 0.663. We get the Result of 1.024(±0.58%) for the TPR20,10 factor of the microLion chamber for the 6MV photon beam with its beam quality TPR20,10 of 0.663 using Monte Carlo simulation. The correction factor is calculated for the microLion chamber and for the 6MV photon beam with its beam quality of 0.665 is and shows good agreements within 0.56% with the one measured (1.024). Conclusion: The beam quality correction factor of the microLion chamber was determined with its correction factor unknown for the 6MV photon. The results from two methods were in good agreements within acceptable uncertainties. There remains a problem that uncertainties associated with microLion chamber should be studied further, but we think the averaged factor 1.0212 could be used for the microLion chamber and for the same photon beam quality as in this study in the reference dosimetry.