Personalized estimates of radiation dose from dedicated breast CT in a diagnostic population and comparison with diagnostic mammography

Abstract

This study retrospectively analyzed the mean glandular dose (MGD) to 133 breasts from 132 subjects, all women, who participated in a clinical trial evaluating dedicated breast CT in a diagnostic population. The clinical trial was conducted in adherence to a protocol approved by institutional review boards and the study participants provided written informed consent. Individual estimates of mean glandular dose to each breast from dedicated breast CT was obtained by combining x-ray beam characteristics with estimates of breast dimensions and fibroglandular fraction from volumetric breast CT images, and using normalized glandular dose coefficients. For each study participant and for the breast corresponding to that imaged with breast CT, an estimate of the MGD from diagnostic mammography (including supplemental views) was obtained from the DICOM image headers for comparison. This estimate uses normalized glandular dose coefficients corresponding to a breast with 50% fibroglandular weight fraction. The median fibroglandular weight fraction for the study cohort determined from volumetric breast CT images was 15%. Hence, the MGD from diagnostic mammography was corrected to be representative of the study cohort. Individualized estimates of MGD from breast CT ranged from 5.7 mGy to 27.8 mGy. Corresponding to the breasts imaged with breast CT, the MGD from diagnostic mammography ranged from 2.6 to 31.6 mGy. The mean (± inter-breast SD) and the median MGD (mGy) from dedicated breast CT exam were 13.9±4.6 and 12.6, respectively. For the corresponding breasts, the mean (± inter-breast SD) and the median MGD (mGy) from diagnostic mammography were 12.4±6.3 and 11.1, respectively. Statistical analysis indicated that at the 0.05 level, the distributions of MGD from dedicated breast CT and diagnostic mammography were significantly different (Wilcoxon signed ranks test, p = 0.007). While the interquartile range and the range (maximum-minimum) of MGD from dedicated breast CT was lower than diagnostic mammography, the median MGD from dedicated breast CT was approximately 13.5% higher than that from diagnostic mammography. The MGD for breast CT is based on a 1.45 mm skin layer and that for diagnostic mammography is based on a 4 mm skin layer; thus, favoring a lower estimate for MGD from diagnostic mammography. The median MGD from dedicated breast CT corresponds to the median MGD from 4 to 5 diagnostic mammography views. In comparison, for the same 133 breasts, the mean and the median number of views per breast during diagnostic mammography were 4.53 and 4, respectively. Paired analysis showed that there was approximately equal likelihood of receiving lower MGD from either breast CT or diagnostic mammography. Future work will investigate methods to reduce and optimize radiation dose from dedicated breast CT.

Digital Breast Tomosynthesis: State of the Art

“…Currently, many DBT systems use tungsten target with aluminum, silver, or rhodium filter (Table 1) and operate at a slightly higher applied tube voltage (kilovolts peak) than FFDM, partly to reduce radiation dose to the breast. Dosimetry protocols used in the United States differ from United Kingdom, European, and IAEA (International Atomic Energy Agency) protocols in terms of assumptions pertaining to fibroglandular fraction and skin layer thickness and its composition (74,75). Dance et al (76) provided a DBT system-specific factor in determining MGD as per United Kingdom, European, and IAEA protocols.…”

Large-angle x-ray scatter in Talbot–Lau interferometry for breast imaging

“…In screening mammography, the mean glandular dose (MGD) from a single craniocaudal view of an “average” breast or breast-equivalent phantom is limited to 3 mGy. For diagnostic evaluation, the average MGD is approximately 10.2 to 12.4 mGy and the average number of views ranges from 3.65 to 4.53 (Law and Faulkner, 2006, Vedantham et al, 2013). This study focused on a system with a FOV that is suited for diagnostic evaluation.…”

Three dimensional dose distribution comparison of simple and complex acquisition trajectories in dedicated breast CT

“…1 but do not include a flat panel detector; instead, the "detector" is actually the target object itself which tracks the dose deposited in each voxel. The exposure of the physical system described above was measured at isocenter with the following technique: 49 kVp tube potential, 1.25 mAs per projection technique, and external tungsten (W, 0.05 mm, ρ = 19.3 g/cm 3 ) filtration, using a calibrated mammography exposure meter (Mammochamber, Model 10x5-6M-3, RadCal), and was found to be 4.11 ± 0.01 mR, which, when converted to air kerma equals 3.576 mGy [see ahead to Eq. (1)].…”

“…Fillable cylindrical phantoms of different diameters (10, 12.5, and 15 cm) and 20 cm height, made of acrylic (ρ =1.19 g/cm 3 ) with a wall thickness of 1.5 mm, were used for this study. The cylinders were initially filled with 100% water, which serves as a surrogate for 100% fibroglandular tissue 32,39 (the Appendix).…”

“…The 12.5 cm cylinder was subsequently filled with a 75% water-25% methanol mixture since it more closely approximates the linear attenuation coefficient of 50% fibroglandular-50% adipose breast tissue 39 (the Appendix) and scanned again with a new sheet of film. A fillable anthropomorphic breast phantom (15 cm maximum diameter and 7 cm depth, 740 ml volume) composed of polyethylene terephthalate (ρ = 1.38 g/cm 3 ) and having a wall thickness of 0.5 mm was also used for the study. The breast phantom, which closely approximates the shape of a clinically encountered human breast, was filled with the 75% water-25% methanol mixture (700 ml) and scanned in a similar fashion.…”