Assessment of Mean Glandular Dose in Mammography
Thesis DisciplineMedical Physics
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
The mean glandular dose (MGD) was measured for a breast phantom by using molybdenum/molybdenum and molybdenum/rhodium target/filter combinations, at different kVp 26, 28 and 32 kilovolts. The phantom thickness was 7.5cm and was made of BR12 material. The change of dose was studied as a function of depth inside the phantom at different depths from the surface, namely 3.3, 4.3 and 5.3cm, by using TLDs. It was found that the MGD value for different combinations of beam quality (HVL) and energy (kVp) did not exceed the recommended values given by different protocols. The Mo/Rh target/filter required lower doses to achieve the same or better results compared with the Mo/Mo target/filter. The change in the surface dose as a function of kVp was more significant for Mo/Rh than for the Mo/Mo. Studying the change in dose within the breast, as a function of depth gives a better understanding of the interactions between radiation and tissue inside the breast. It should be noted that the MGD is a tool for optimization of the mammography parameters. However, the MGD should not be used directly to estimate the risk of determinable health effects from mammography. This will ultimately help to determine limits for the breast surface dose and a better understanding of cancer risk. In future work, we will try to measure the change of the dose as a function of depth by using more kVp, HVL, different breast composition and different target/filter combinations to give a wider picture for different situations.