Absorbed dose ratio factor of Al_2O_3 in 6 MV radiotherapeutic beams

The EGSnrc Monte Carlo codes of BEAMnrc, DOSXYZnrc and DOSRZnrc were used to simulate absorbed dose of an Al2O3 dosimeter and absorbed dose of the equivalent water volume in corresponding position irradiated by radiotherapeutic Varian 600C 6 MV beams and Mohan 6 MV spectrum in a water phantom.The absorbed dose ratio factor fmd was calculated, and dosimetry characteristics of the Al2O3 dosimeter were discussed.Simulations were done for a cylindrical geometry dosimeter(Φ4 mm×1 mm) and the dosimeter was at the centre of the water phantom at different depths of 0.5-8.0 cm.The results reveal that the absorbed dose of the Al2O3 dosimeter is less than that of the equivalent water.The absorbed dose ratio factor is dependent on the dosimeter depth in the phantom.In the buildup region the absorbed dose ratio factor fmd is sensitive to the depth of the dosimeter.Over the buildup region fmd is insensitive to the depth.This allows the use of averaged absorbed dose ratio factor without introducing discrepancies more than 1.0%.