Experimental dose estimation in anthropomorphic breast phantom in clinical mammography systems

摘要

The aim of this work is to estimate the percentage depth dose (PDD) and the mean glandular dose (MGD) at anthropomorphic breast phantoms using calibrated TLDs. For this task the TLD-100H was initially selected and calibrated in terms of air kerma, using a Radcal ionization chamber (IC). The experimental procedure was performed at a mammograph Mammomat 3000 Nova, located at the CDTN/CNEN facilities and all the detectors were exposed with 28 kV with distinct anode/filter combination (Mo/Mo, Mo/Rh and W/Rh). Furthermore, the TLDs were placed at the surface of anthropomorphic compressed breast phantoms (36-85 mm) and at 1,2 cm for depth doses measures, for PDD analyses. The MGD were estimated from entrance surface doses and using Dance's method. The dose-response curves for the TLDs indicated a good correlation coefficient (R~2 = 0,99) for all anode-filter combination with an uncertainty lower than 17%. The uncertainties of the measurements increased to maximum 35 % when the TLDs are placed the anthropomorphic breast phantom. The PDD were maximum 70%, at 1,2 cm, for the Mo/Mo target-filter combination. Regardless the target/filter (T/F) combination, the TL responses and consequently the MGDs substantially increased with the breast thickness. A maximum MGD of approximately 4.5 mGy was estimated for the 85 mm thickness breast, exposed to the Mo/Mo combination.