Evaluation of glandular dose in mammography in the presence of breast cyst using Monte Carlo simulation

Introduction:
Average glandular dose (AGD), entrance skin air kerma (ESAK) and normalized glandular dose (DgN) are the main dosimetric quantities in mammography. In this study, DgN is evaluated in the presence of breast cyst, which is a common disease among women and the influence of size, number and location of the cysts on the DgN is investigated.
Materials and Methods:
Payamed mammography unit was simulated by MCNPX Monte Carlo code and the validation of the simulation was performed by comparing the photon spectrum and percentage depth dose from the simulations by the other studies and measurement. DgN was assessed in the presence of breast cysts. This was performed by simulation of a homogeneous breast phantom which contained spherical cysts. These cysts were in different sizes, numbers and positions. DgN values were compared for the cystic phantom by those related to a normal homogenous phantom without cyst.
Results:
The results of the simulation in this study are in agreement with the other studies and the validation of the simulation results is confirmed. In the cystic phantom the DgN values have differences ranging from -7% to +14% compared with the normal breast phantom. The results show that the DgN in presence of cysts in the breast phantom depends on the size, number and positon of cysts, but it is independent of breast thickness, glandular fraction and tube voltage.
Conclusion:
Even though the breast cyst is a high prevalent disease in women over 35 years, this effect has a little impact on dose calculation in mammography. Howevere, in the case of large sizes and various number of cysts the influence of presence of cysts in the breast is considerable. It is recommended that, if it is possible, the effect of the presence of breast cysts on normalized glandular dose calculation be taken into account in dosimetry in mammography.