M3D: Mammography phantom to assess mean glandular dose using thermoluminescent dosimetry

Abstract

Mean Glandular Dose (MGD) is obtained from air kerma measurements, compressed breast characteristics, and beam quality, usually using an ionization chamber (IC). We have developed a system called M3D to evaluate MGD using thermoluminescent dosimetry. The system consists of two PMMA phantoms, one to obtain the radiological techniques for different breast thicknesses and the other to measure air kerma and half-value-layer. In this work, we have redesigned the first phantom to have a variable thickness, and we have evaluated two alternative methods for the use of thermoluminescent dosimeters to measure the required kerma and half-value-layer: use of TLD-100 and Al foils, or a combination of TLD-100/ TLD-300. In the second method, the TLD-300 glow curve shape was analyzed as a vector and was used to determine beam quality. Results showed that the kerma measured by both methods were equivalent to the use of an IC. Typical MGD uncertainties were about 14% and 35% for the two methods, respectively, and these figures rule out the use of the TLD-100/TLD-300 combination for this application. We have concluded that the newly designed M3D system is an option to determine MGD for different breast thicknesses.