Author: Larry A. DeWerd, Keith A. Kunugi, Autumn Rasmussen 👨🔬
Affiliation: Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin - Madison 🌍
Purpose: Ensuring the validity of the thermoluminescent dosimeter (TLD) response requires verifying that signal fading—defined by a reduction in stored signal—is well-known and corrected for under the specified time, temperature, and dose conditions. This study aimed to determine whether TLDs exhibit fading distinct from temporal fading when held at 37°C, a temperature relevant to in vivo conditions for humans and mice, over one week to several months.
Methods: To characterize possible TLD fading at body temperature, LiF:Mg,Ti TLDs of chip geometry were sorted and characterized using the method described by Cameron et al. (1986). The TLDs were acutely exposed using a 137Cs source. The dosimeters received doses ranging from 25 cGy to 300 cGy. They were stored in darkness at either room temperature or 37℃. Readouts were conducted using a Harshaw 5500 TLD reader and performed weekly for 3 months. All results were corrected for background signal.
Results: LiF:Mg,Ti TLD chip measurements indicated no statistically significant fading effects across the implemented time-temperature-dose scale, with an uncertainty of 2.8% at k=1. The TLD responses exhibited linearity with dose, consistent with the expected behavior in the studied dose region and the known trap half-lives of LiF:Mg,Ti.
Conclusion: The results of this study support that TLDs are reliable dosimeters for long-term in-vivo applications, as no significant fading was observed when held at body temperature over extended periods of time. This stability under biologically relevant conditions, coupled with linearity in response over the specified dose range, underscores their potential utility in diverse medical physics applications. These findings further support the integration of TLDs into protocols requiring extended-duration radiation monitoring without compromising accuracy.