Charge collection efficiency determination for a Farmer-type ion chamber through different recommended methods

Abstract

Incomplete charge collection efficiency of employed ion chamber for high energy photon dosimetry is one of the main concerns which should be compensated. In this regard, a correction factor, known as recombination correction factor (Ks), has been introduced by different methods. The aim of this study is to measure and compare the obtained Ks values by different recommended protocols for a Farmer-type ion chamber at different chamber voltages and dose rates.30013 Farmer-type ion chamber (PTW) was considered in this study. Global dosimetry protocols including TRS-398 and TG-51 ones as well as the dose per pulse (DPP) method and Jaffe-plot approach were employed for Ks evaluation at various voltages of 200, 300, and 400 V and machine dose rates of 50, 100, 200, and 350 MU/min.The results showed that the obtained Ks values by different methods are very consistent so that the difference between the results was below 0.2% in all cases. Ks values were dependent on the applied voltage to the ion chamber, such that increasing the chamber voltage would reduce the Ks value. On the other hand, variations of the machine dose rate (MU/min) don't considerably affect the Ks value.Finally, it can be concluded that the different recommended approaches for Ks determination would result in analogous values (in comparison with the Jaffe-plot data as reference one). Therefore, the performance accuracy of studied approaches for simplified Ks determination has been confirmed.