Duke Radiation Safety
 
Radiation Dose to the Breast From Mammography

Parameters for Computing Radiation Dose

Mammography This program uses parameterized data tables developed by Wu and colleagues (see "References" below) to compute radiation dose to the breast consequential to mammography. You can vary the thickness of the breast, the composition of the breast tissue and other variables to determine their effect on breast dose.

Complete the form below and click the "Compute Dose" button to calculate the radiation dose factor (millirads per roentgen of skin entrance exposure) for glandular breast tissue. Make sure you enter values for the parameters you wish to vary, consistent with the appropriate units. If you leave a field blank, a default value [shown in brackets] will be used. See "Notes" below for valid ranges for the parameters.

Enter kVp (kilovolts): [25]
Enter Filtration Half-Value Layer (mm aluminum): [.265]
Enter Thickness of Compressed Breast Tissue (cm): [4]
Enter Glandular Fraction (0.0 - 1.0): [.50]
Enter Skin Entrance Exposure (roentgens): [variable]

Target / Filtration Combination (Select One):

Molybdenum / Molybdenum Molybdenum / Rhodium Rhodium / Rhodium

All Done? Compute the Glandular Tissue Dose Factor:

Notes and References

This program is based on work by Wlad T. Sobol and Xizeng Wu, Department of Radiology, University of Alabama Hospitals and Clinics. The parameterization code originally appeared in their article entitled "Parametrization of Mammography Normalized Average Glandular Dose Tables", Medical Physics 24(4): 547 - 554 (April 1997).

Default values for the parameters, including the skin entrance exposure, are based on work by Xizeng Wu, Gary T. Barnes and Douglas M. Tucker, which appeared in their article entitled "Spectral Dependence of Glandular Tissue Dose in Screen-Film Mammography", Radiology 179: 143 - 148 (1991).

Notes:

1. Peak kilovoltage (kVp) should be between 23 and 35 kilovolts.

2. Filtration (mm AL) should be between 0.24 and 0.43 mm.

3. Breast tissue thickness refers to the compressed breast, as measured in the center of the field of view. Values should be between 2 and 8 cm.

4. "Glandular fraction" refers to the composition of the breasts, as partitioned between glandular tissue (the radiation-sensitive component) and adipose tissue. So-called "fatty breasts" or "fibrous breasts" would have a value of glandular fraction closer to 0.0; "dense breasts" would have a glandular fraction closer to 1.0. Breast tissue composed of half adipose tissue and half glandular tissue would have a glandular fraction of 0.50.

5. Skin Entrance Exposure is the exposure (roentgens) for a particular mammographic technique, as measured free in air above the surface of the breast. The value used depends on technique (kVp, mAs, filtration, etc.), and will vary considerably based on breast thickness. Typical values range between 0.5 R (thin breasts) and 5.0 R (thick breasts). The program supplies default values based on the entered value for breast thickness.

6. Target / Filter Combination: select a value appropriate for the system under investigation.

If the data entered in the form exceed the specified ranges, the calculation will not be performed. This prevents the computation of dose factors based on extrapolation beyond accepted values for the parameters, and resulting instabilities in the parameterization functions.

Important Information Concerning This On-line Material

This material is for use by Duke University Radiology physicians and staff. It is intended to be a convenient reference for estimating radiation dose to glandular breast tissue from mammography, under the stated conditions. It should not be used as a primary source of information regarding mammography dosimetry. Because these calculations of breast dose are based in part on data obtained from "phantoms", they are not strictly applicable to any individual patient. They are suitable for comparisons between techniques only. Duke University and OESO make no warranty as to the suitability of these dose computations for any other purpose.

For Questions or Comments, Contact...

Robert E. Reiman, MD
General Secretary, DUMC Radiation Safety Committee
reima001@mc.duke.edu
(919)684-2194

Copyright 2000, Robert E. Reiman, MD, OESO and Duke University Medical Center. All rights reserved.