Towards in vivo TLD dosimetry in mammography

While phantoms are used for quality control assessment of the mammography unit, in vivo dose measurements are necessary to account for the variation in size and composition of the female breast. The use of thermoluminescent dosimeters (TLDs) in mammography has been limited due to TLD visibility. The aim of this current investigation was to access the suitability of a paper-thin LiF:Mg,Cu,P TLD (GR-200F) for in vivo dosimetric mammography measurements. The visibility of GR-200F has been directly compared with LiF:Mg,Cu,P TLDs (GR-200A) using a number of commercially available phantoms. The phantoms of thickness 2-5 cm were imaged over the range of tube potentials (24-28 kVp) used clinically. Both types of TLD were placed on the surface of the phantoms allowing assessment of visibility, entrance surface dose (ESD) and field homogeneity. In vivo assessment of ESD and visibility was also carried out on a volunteer undergoing a routine mammography examination. The positions of the GR-200F TLDs were not identified either on the image of the Leeds TOR(MAM) phantom or the patient mammograms. The average ESD for the Leeds phantom was 8.8 mGy, while the patient ESD was 13 mGy. It is now possible to perform in vivo measurements with the potential of increasing the accuracy of the doses measured for women that do not conform to a standard breast thickness or density.