Computation of the glandular radiation dose in digital tomosynthesis of the breast
Diagram specifying the measurement location of the two projection angles related by Eq. (1).
Diagram specifying the location to which the unit exposures in the normalized glandular dose values are referenced.
Diagram of the simulated MLO view. (a) Top view, (b) Side view. The pectoralis muscle’s thickness decreases towards the caudal side. The length of the pectoralis muscle along the chest wall varies so that the lower edge aligns horizontally with the nipple. -wall to nipple distance, breast thickness.
Diagram of the simulated CC view. -wall to nipple distance, breast thickness.
Comparison of the linear attenuation coefficients reported by Hammerstein et al. (Ref. 28) (symbols) and those resulting from the developed Geant4 program (lines). Excellent agreement can be seen for all three glandular fractions.
Total linear attenuation coefficients and their decomposition into the three relevant physical interaction processes for the simulated breast tissue with 50% glandular fraction. The symbols are National Institute of Standards and Technology’s XCOM data (Ref. 30) and the lines show the data obtained from the developed Geant4 program. Similar agreement was found for the 100% adipose and the 100% glandular breast tissues.
Comparison of values computed by the Geant4 program against those previously reported by (a) Wu et al. (Ref. 18) and (b) Boone (Ref. 21). The lines represent the linear fit that result in the displayed equations. Excellent agreement is observed in both cases.
Sample graphs of RGD variation with varying (a) breast glandular fraction, (b) x-ray spectrum, (c) chest-wall to nipple distance, (d) compressed breast thickness. All four graphs are for MLO view, , , and Mo-Rh x-ray spectrum, unless specified otherwise. Positive angle projections are defined as when the x-ray tube swings towards the cranial side of the patient. Note the different -axis scale in Fig. 8(c).
Sample graphs of RGD variation with varying (a) breast glandular fraction, (b) x-ray spectrum, (c) chest-wall to nipple distance, (d) compressed breast thickness. All four graphs are for CC view, , , and Mo-Rh x-ray spectrum, unless specified otherwise.
Graphs of RGD vs projection angle for (a) , , and (b) , , both for the MLO view.
Graph of RGD vs projection angle for a small breast in MLO view showing the variation due to placing the breast on the center of the detector rather than towards the superior side. The RGD distribution for the MLO detector-centered breast is compared with the standard MLO view for the same sized breast and with the CC view data for the breast with equivalent mass and thickness.
Graphs of RGD vs projection angle for three different detector to x-ray tube center of rotation distances. Graph (a) is for a CC view breast with , (b) is for a MLO view breast with . For both graphs , and the x-ray spectrum is Mo-Rh .
First half-value layer values of the x-ray spectra used to combine the mono-energetic Monte Carlo results. The mono-energetic results were combined using the computed HVL above the breast compression plate due to the inclusion of the breast compression plate in the simulation.
Mean computed normalized glandular dose per unit exposure at the intersection of the central ray and the breast support plate (see Fig. 2) for zero degree projection angle, (mGy/R). For MLO view data, breasts with a chest-wall to nipple distance of less than have a lower by 6%–14%, for larger breasts the data deviates from the mean reported here by a maximum of 6%. For CC view data, the data deviates from the mean by a maximum of 3%.
Sensitivity of the relative glandular dose, , to the simulation parameters studied in this work.
Coefficients for the fit Eqs. (3) and (4) to compute relative glandular doses, , for both the MLO and CC views.
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