New NIST reference mammography beams using a tungsten target and silver, rhodium, molybdenum and aluminum filters at 20 kV to 50 kV have been developed.
These beams will provide FDA inspectors, ionization chamber manufacturers, and calibration facilities with the techniques that best represent what is used in clinics. These new reference radiation techniques will be available for calibrations and the FDA-MQSA proficiency tests. The NIST 100 kV tungsten anode x-ray unit and the Ritz primary standard free-air ionization chamber are being used for the digital mammography techniques. Air-attenuation corrections have been measured directly, and other correction factors have been calculated with Monte Carlo methods using measured beam energy spectra. Correction factors will be determined for various anode/filter combinations, including W/Ag, W/Rh, W/Mo and W/Al, with and without 2 mm Al additional filtration, in 5 kV increments between 20 kV and 50 kV. Upon final determination of the corrections, the air kerma will be realized, allowing for an indirect comparison with another NMI that supports these reference radiations.