Purpose: Determine the energy spectrum and ranges of secondary electrons generated in the vasculature during a high-energy contrast-enhanced mammography exam. Of particular interest is the impact iodine has on the quantity and energy of liberated electrons.
Methods: A Monte Carlo simulation of a high-energy exposure from a contrast-enhanced mammography exam was run in PHENX using a virtual realistic breast phantom generated using the VICTRE pipeline. Three identical cylinders, 2mm in diameter and 2 cm in length, were inserted in the middle of the phantom at the same vertical position with centers 2 cm apart from each other. Each cylinder was filled with whole blood (ICRP) for one simulation and whole blood mixed with a concentration of 2 mg/mL of iodine for another. PHENX reported the energy and interaction type of each secondary electron produced within the volumes of interest. CSDA ranges of electrons in A-150 tissue-equivalent plastic from the National Bureau of Standards were used to analyze the spectrum of electron ranges present based on the reported output.
Results: The introduction of iodine into the cylinders increased the total number of liberated secondary electrons by 14.9%. Of these, nearly 27% had ranges greater than 9.5 microns. In both runs, around 42% of secondary electrons had energy ranges greater than 2.5 microns, which is the lower end of capillary radius in the body.
Conclusion: Iodinated contrast agent in the circulatory system during contrast-enhanced mammography exams increases the number of secondary electrons that have sufficient energy to escape capillaries and small vessels, which will increase dose to surrounding tissues. The associated impact on dose to glandular tissue and the related effect on radiation-induced carcinogenesis is still under investigation.
Monte Carlo, Contrast Agent, Mammography