Comparison of IAEA absorbe dose protocols TRS 277, TRS 381 and TRS 398 for different electron energies

OBJECTIVES: In this study, calculation of absorbed doses according to three different IAEA protocols for 6, 8, 10, 12, 15, and 18 MeV electron energies were compared. METHODS: Absorbe dose measurements were made at SSD=95 cm distance, 10 x 10 cm standart cone and reference depth. Electron energies was measured with five different cylindirical chambers and three different paralel plate chambers. Polarity and recombination effects were measured for all ionization chambers and energies before absorbed dose measurements. RESULTS: After the measurements, calculations were made according to three different protocols. For Marcus parallel plate chambers, the ratio of absorbe dose protocols was between -2.04% to 2.64%. Except from Marcus for other parallel plate chamber difference was between 0.11% to 3.38% for 6 MeV, 0.33% to 1.37% for 8 MeV, 0.12% to 1.71% for 10 MeV, 1.35% to 0.23% for 12 MeV, 1.69% to 0.24% for 15 MeV and 0.22% to 1.74% for 18 MeV. CONCLUSION: Contrary to photon energies, difference between absorbe dose protocols for electron beam energies was high. The reason of the difference was arise from the fact that TRS 277 assumes perturbation factor of parallel plate chambers was “1”. As a result, TRS 398 protocol enables us to calculate much more accurate absorbe dose.