Analysis of TLD-100 Calibration and Correction Factor in Different Field Sizes Under Low Dose Conditions Irradiated with Two Systems: Gamma Knife 4C and Theratron 780-C

Abstract

Purpose: Nowadays in most researches, thermoluminescent dosimeters are used as a practical implement for dosimetry systems. In this study, we calibrated thermoluminescent dosimeters by Gamma knife 4C and Theratron 780-C units as gamma emitters in low dose conditions and moreover compared the response of both calibration curves to consider possibility of using every device’s calibration curves instead of the other instrument.
Materials and Methods: Calibration curves of Theratron 780-C machine and Gamma knife 4C unit were measured and plotted in low dose conditions. In order to conduct individual calibration, TLDs were exposed with dose of 100 cGy and through group calibration, dosimeters were divided into 7 groups and were exposed with doses of 0-12 cGy in both machines. To evaluate TLD response by changing field size, TLDs were irradiated with different field sizes in Theratron 780-C and with different collimator sizes in Gamma knife 4C. The best fitting curves were obtained with Excell and Matlab software.
Results: By complying with the best fitting curves for the TLD-100 and conforming to Fisher's test, calculated p-value was 0.92, which was greater than 0.05, therefore the difference is not significant between two calibration curves.
Conclusions: Regardless of differences in calibration conditions between Theratron 780-C machine and Gamma Knife 4C unit, the results showed that every one of these devices can be replaced and used to estimate the unknown dose both in stereotactic radiosurgery and radiotherapy.