Dedicated cone‐beam breast CT: Data acquisition strategies based on projection angle‐dependent normalized glandular dose coefficients

Abstract

Background: Dedicated cone-beam breast computed tomography (CBBCT) using short-scan acquisition is being actively investigated to potentially reduce the radiation dose to the breast.This would require determining the optimal x-ray source trajectory for such short-scan acquisition. Purpose: To quantify the projection angle-dependent normalized glandular dose coefficient (DgN CT ) in CBBCT, referred to as angular DgN CT , so that the x-ray ray source trajectory that minimizes the radiation dose to the breast for short-scan acquisition can be determined. Materials and Methods: A cohort of 75 CBBCT clinical datasets was segmented and used to generate three breast models -(I) patient-specific breast with heterogeneous fibroglandular tissue distribution and real breast shape, (II) patient-specific breast shape with homogeneous tissue distribution and matched fibroglandular weight fraction, and (III) homogeneous semi-ellipsoidal breast with patient-specific breast dimensions and matched fibroglandular weight fraction, which corresponds to the breast model used in current radiation dosimetry protocols. For each clinical dataset, the angular DgN CT was obtained at 10 discrete angles, spaced 36 • apart, for full-scan, circular, x-ray source trajectory from Monte Carlo simulations. Model III is used for validating the Monte Carlo simulation results. Models II and III are used to determine if breast shape contributes to the observed trends in angular DgN CT . A geometry-based theory in conjunction with center-of -mass (COM) based distribution analysis is used to explain the projection angle-dependent variation in angular DgN CT . Results: The theoretical model predicted that the angular DgN CT will follow a sinusoidal pattern and the amplitude of the sinusoid increases when the centerof -mass of fibroglandular tissue (COM f ) is farther from the center-of -mass of the breast (COM b ). It also predicted that the angular DgN CT will be minimized at x-ray source positions complementary to the COM f . The COM f was superior to the COM b in 80% (60/75) of the breasts. From Monte Carlo simulations and for homogeneous breasts (models II and III), the deviation in breast shape from a semi-ellipsoid had minimal effect on angular DgN CT and showed less than 4% variation. From Monte Carlo simulations and for model I, as predicted by our theory, the angular DgN CT followed a sinusoidal pattern with maxima and minima at x-ray source positions superior and inferior to the breast, respectively. For model I, the projection angle-dependent variation in angular DgN CT was 16.4%. Conclusion:The heterogeneous tissue distribution affected the angular DgN CT more than the breast shape. For model I, the angular DgN CT was lowest when the x-ray source was inferior to the breast. Hence, for short-scan CBBCT 1406

Dedicated Cone-Beam Breast CT: Reproducibility of Volumetric Glandular Fraction with Advanced Image Reconstruction Methods

“…In an effort to translate BCT to breast cancer screening, multiple research teams and industrial partners are working on various hardware approaches including the use of highresolution, low-noise, complementary metal oxide semiconductor (CMOS) detectors [25] either with full-scan [25,26] or short-scan acquisition [27,28], or photon-counting detectors with helical acquisition [29]. The primary objective of these research efforts is to reduce the radiation dose so that it is appropriate for screening exams while improving the visualization of microcalcifications.…”