Abstract
Purpose: To characterize the component of the LiF:Mg,Ti TLD response to the low‐energy photons of and LDR brachytherapy sources and x‐ray beam qualities of M40 and M80, that cannot be predicted by cavity theory or Monte Carlo methods. To provide a methodology for determining accurate energy correction factors for experiments performed in a variety of scatter conditions and to provide an example of how to apply the results of this work will also be presented. Method and Materials: TLD‐100 chips were exposed to and LDR brachytherapy sources using the known geometry of the University of Wisconsin Variable Aperture Free Air Chamber. Dose calculations were based on primary determinations of air‐kerma strength and Monte Carlo simulations of the full irradiation and source geometry. For comparison purposes and to examine the effects of dosimeter size and scatter conditions, a series of x‐ray experiments were performed to compare the response of chips (3×3×0.89mm) to microcubes (1×1×1mm) and free in air irradiations to irradiations in a PMMA holder. Results: The results of the x‐ray experiments agreed well with the work of Nunn et al. (Med. Phys. 2006) and confirmed that the “solid‐state” component of the energy response was largely independent of irradiation geometry. The results of the experiments exhibited good reproducibility for the single source, but the measurements seem to exhibit source‐to‐source variability. More experiments are needed for both isotopes to determine the nature of these observations. Conclusion: For all radiation qualities used in these experiments it was found that Monte Carlo simulations appear to underestimate the dose response of LiF:Mg,Ti when compared to measured response. As a result, the previously published values for the dose rate constants of LDR brachytherapy sources are likely overestimates.
Published Version
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