Angular normalized glandular dose coefficient in breast CT: clinical data study

Abstract

The goal of this study is to understand how the normalized glandular dose coefficient (𝐷𝑔𝑁𝐶𝑇) varies with projection angle in dedicated cone-beam breast computed tomography (CBBCT). Seventy-five CBBCT clinical datasets from a research database were used for this study. All samples were segmented into skin, adipose and fibroglandular tissues. The segmented volumes were used in a Monte Carlo simulation package (GATE 8.0) to estimate the radiation dose at 10 angles in a full scan. An analytical model is proposed, and this model predicted that the angular 𝐷𝑔𝑁𝐶𝑇 follows a sine wave and the maximum is related to the center of geometry of the fibroglandular tissue (COGf ). The angular 𝐷𝑔𝑁𝐶𝑇 from Monte Carlo simulations was consistent with our model and follows a sine wave with amplitude of 0.0376. The maximum of the wave occurs when the x-ray source is approximately at head position, which is consistent with our model. Our results indicate that the higher angular 𝐷𝑔𝑁𝐶𝑇 occurs when the x-ray source is superior to the breast. This suggests using a x-ray source trajectory inferior to the breast for short-scan CBBCT design.