Three dosimetry calibration laboratories accredited by the American Association of Physicists in Medicine (AAPM) routinely perform calibrations of a large number of instruments used in hospitals across the U.S. for medical applications.
Measurements provided by these accredited dosimetry calibration laboratories (ADCLs) are directly traceable to the national standard for absorbed dose to water and air kerma from 60Co therapy level gamma ray beams. This is achieved by the use of high quality ionization chambers that are sent by the ADCLs to NIST for calibration. In addition to calibrations, all three ADCLs participate periodically in a proficiency test (blind test) with NIST. The most recent test was carried out during the first part of the year 2012. Calibrations of ionization chambers performed in the NIST 60Co therapy level reference beams contribute to a number of other ongoing projects at NIST and elsewhere. These include work in support of the development of air kerma and absorbed dose standards in high energy x-ray beams produced by linacs and proton beam accelerators. Passive dosimeters including different types of radiochromic film and thermoluminescent dosimeters are also characterized in these facilities.