ABSTRACT
Several codes of practice based on absorbed dose to water for reference dosimetry in clinical high-energy photon and electron beams have been published recently, to replace the air-kerma based codes of practice. In the present work, comparative dosimetry has been done utilizing absorbed dose based recommendations [AAPM TG-51 and IAEA TRS-398] and four air -kerma based recommendations [NCS report-5 and IAEA TRS-381]. Measurements were performed for five clinical electron beam energies [5MeV. 7MeV, 10MeV, 12MeV, and 14MeV] using three Markus-type plane-parallel chambers. Dosimetry based on direct calibrations of all chambers using [50]Co was investigated. It is shown that the use of [60]Co calibration factors could result in deviations of up to 2.3% in electron beams using different codes of practice. The results show that the obtained absolute dose values at the depth of maximum dose D[max] are not significantly altered by changing from air-kerma based dosimetry to absorbed dose to water based dosimetry when using calibration factors obtained from the Laboratory for Standard Dosimetry. National Institute of Standards, Egypt