The effect of skin thickness determined using breast CT on mammographic dosimetry

Abstract

The effect of breast skin thickness on dosimetry in mammography was investigated. Breast computed tomography ͑CT͒ acquisition techniques, combined with algorithms designed for determining specific breast metrics, were useful for estimating skin thickness. A radial-geometry edge detection scheme was implemented on coronal reconstructed breast CT ͑bCT͒ images to measure the breast skin thickness. Skin thickness of bilateral bCT volume data from 49 women and unilateral bCT volume data from 2 women ͑10 healthy women and 41 women with BIRADS 4 and 5 diagnoses͒ was robustly measured with the edge detection scheme. The mean breast skin thickness ͑Ϯinter-breast standard deviation͒ was found to be 1.45Ϯ 0.30 mm. Since most current published normalized glandular dose ͑D gN ͒ coefficients are based on the assumption of a 4-mm breast skin thickness, the D gN values computed with Monte Carlo techniques will increase up to 18% due to the thinner skin layers ͑e.g., 6-cm 50% glandular breast, 28 kVp Mo-Mo spectrum͒. The thinner skin dimensions found in this study suggest that the current D gN values used for mammographic dosimetry lead to a slight underestimate in glandular dose.

Technical Note: Skin thickness measurements using high‐resolution flat‐panel cone‐beam dedicated breast CTa)

“…Thus, the study participants were from a geographically different location compared to the previous study. 13 The study enrolled 150 subjects, all women, from which 137 dedicated breast CT volumes from 136 women (135 unilateral exams, 1 bilateral exam) were included in this analysis. All dedicated breast CT exams were performed after assignment of BI-RADS R 4 or 5 as per the American College of Radiology assessment categories 14 and prior to tissue sampling (biopsy).…”

“…The method described in previous reports 13,19 were followed for consistency in the breast skin thickness estimate, with a few modifications in implementation. In order to describe the modifications, a synopsis of the method 13 along with the modifications is provided. The steps involved were: manually defining the breast volume used for determining the breast skin thickness; 17,19 segmenting the breast volume from the background (air), for which we used an algorithm 20,21 different from the prior study; 13 transforming each coronal slice to polar coordinates, for which we used 1 • angular steps and applied and a 3 × 3 median filter prior to polar transform; followed by applying a one-dimensional (1D) derivative filter to obtain the gradient image.…”

“…The clinical prototype dedicated breast CT system [15][16][17] used in this study was different from the previous study. 13 FDK reconstruction 18 that provided isotropic (0.273 mm) 3 voxels were used. The method described in previous reports 13,19 were followed for consistency in the breast skin thickness estimate, with a few modifications in implementation.…”

“…13 FDK reconstruction 18 that provided isotropic (0.273 mm) 3 voxels were used. The method described in previous reports 13,19 were followed for consistency in the breast skin thickness estimate, with a few modifications in implementation. In order to describe the modifications, a synopsis of the method 13 along with the modifications is provided.…”

“…Prior studies [1][2][3][4][5][6][7] on Monte Carlo-based estimation of normalized glandular dose coefficients for mammography and digital breast tomosynthesis assume the breast skin thickness to be 4-5 mm. The range of breast skin thickness estimated from mammography has been reported as 0.5-1.5 mm by Witten, 8 0.5-2.0 mm by Hoeffken and Lanyi, 9 0.8-3.0 mm by Willson et al, 10 0.5-2.7 mm by Pope et al, 11 and 0.5-3.1 mm by Ulger et al 12 Recently, Huang et al 13 determined the breast skin thickness using dedicated breast CT and investigated its impact on mammographic dosimetry. They observed that the breast skin thickness averaged over multiple locations was in the range of 0.9-2.3 mm with a mean of 1.45 mm from 100 breasts.…”