THE STUDY OF ABSORBED DOSE DETERMINATION IN HIGH ENERGY ELECTRON AND PHOTON BEAMS USING NEW CODE OF PRACTICE IAEA-TRS 398 COMPARED WITH IAEA-TRS 277

Abstract

In Thailand, the Secondary Standard Dosimetry Laboratory (SSDL) provided the calibration factors to the hospitals all over the country for the absorbed dose determination in external beam radiotherapy using IAEA- TRS 277 protocol. The SSDL started the project of using TRS 398 protocol instead of TRS 277 protocol by providing the N_D.W factors for the hospitals who participated in the project. Three university hospitals fromten ‘hospitals which participated in this project were selected for analyzing the absorbed dose determined by TRS 398 compared with TRS 277. For photon beams, the measurement were performed in water phantom for 6 and 10 MV x-ray beams and Cobalt-60 gamma beams with NE 2571 0.6 cc thimble chamber. For electron beams, the cross calibration of PTW 23343 Markus chamber with NE 2571 chamber were performed to derive the N_D.W factor for the highest electron energy. Then the dose measurement of the highest electron beams were undertaken with Markus chamber in water phantom. The results show the comparable of absorbed dose to water of photon beams determined by both TRS 398 and TRS 277 with the maximum discrepancy of 0.9%. But for electron beams, the maximum discrepancy is high up to 5%. The complicated technique of electron measurement may cause the uncertainty both in the measurement and also in the absorbed dose determination. Before the implementation of the new code of practice, JAN. - APR. 2004. Volume X Number| studying and understanding the code of practice is necessary.