New results on short-term annealing for clinical TL dosimetry

Traditional annealing procedures for lithium fluoride are time-consuming and last between 6 to 24 hours; they allow one read-out cycle a day only. This represents problems especially in clinical routine if the number of detectors is limited. A short-term annealing procedure was developed in 1971 for the use in radiation protection with doses below 0.1 Gy. This method enables the user to perform a large number of read-out cycles a day. The present study shows a modified short-term annealing cycle that can also be used in radiation therapy for dose levels between 0.5 and 6 Gy. The procedure requires about 1 h annealing time in total, including heating-up, 15 min at 400 degrees C and an oven specific cooling-down profile. It can be applied without any drawback in precision. No further temperature treatment like e.g. thermal stabilization, was used in the present investigations. The low temperature peaks have been eliminated by using a self-developed computerized glow curve analyzis software. A reproducibility test with 10 measuring cycles yielded precision of 0.2-0.4 % (1 s. d.) for individual LiF:Mg,Ti (TLD-100) chips. Further advantages of the described annealing procedure are an increase of response and a reduction of supralinearity. (author)