An Air Core Scintillation Dosimeter for Megavoltage External Beam Dosimetry: Experimental Results

摘要

plastic scintillation dosimeter, using an air core light guide to transport the scintillation signal, has been shown to be free of the unwanted Cerenkov background signal that usually results from exposure of fibre optics to megavoltage photon and electron radiation beams. We report the performance of the air core dosimeter in 6 MV and 18 MV photon beams and 6 MeV and 20 MeV electron beam. The percentage depth dose measurements for both photon beams agree with ionisation chamber measurements to within 1.6%, for depths up to 250 mm, except in the build up region where the positional uncertainty results in a slightly larger deviation. For a 6 MeV and 20 MeV electron beam, the percentage depth dose measurements agree with the ionisation chamber measurements to within 3.6% and 4.5% respectively. For small radiation fields, readings agree with diamond detector readings to within 1.2% for field sizes of 10 x 10 cm down to 1 x 1 cm. The air core dosimeter's performance in two dynamic IMRT test fields agrees well with ionisation chamber measurements whether the dosimeter is located in a high dose region or in a low dose region.