Radiation dose to organs and tissues from mammography: Monte Carlo and phantom study

Purpose: To prospectively determine the radiation dose to the organs of the body during standard bilateral two-view mammography by using Monte Carlo simulations and a phantom. Materials and Methods: A modified version of the Cristy mathematic anthropomorphic phantom was implemented in the Geant4 Monte Carlo tool kit to simulate the conditions present in screen-film and digital mammography. The breast was simulated with compression in both the craniocaudal and the mediolateral oblique views. X-rays were tracked from the source until their absorption in the body or in the detector or their exit from the simulation limits, with recording of all the intermediate interactions in the body. The simulation was performed with x-rays of energy ranging from 6 to 35 keV to obtain results for clinically relevant spectra. The ratio of dose to an organ in the body per unit glandular dose to the breast, denoted the relative organ dose (ROD), was computed. The effect of using a body protective shield was also investigated. Results: The organs that received an ROD of 0.10% or higher in at least one view and one spectrum were the contralateral breast, ipsilateral eye and eye lens, heart, ipsilateral lung, and thymus. Among the organs, the maximum ROD was 0.62%. The maximum ROD for the bone surfaces was 2.36% and that for the red bone marrow was 0.56%. The highest ROD measured for the uterus or fetus at the first trimester was less than 10^-5. Conclusion: The radiation dose to all tissues other than the breast is extremely low. The dose to the first-trimester fetus is minimal.