In an effort to meet the needs of calibration facilities which offer NIST traceable calibrations of air kerma measuring instruments used in the mammography energy range, NIST will offer proficiency tests. The FDA-MQSA " Final Rule for Quality Mammography Standards" requires that all clinical mammography units be calibrated with an instrument that is traceable to a national standard. The facility that provides the NIST traceable calibration must participate in a biennial proficiency program directly with NIST. The calibration facility must show a 3 % agreement with the national standard in the mammography energy range.

Proficiency Tests for Mammography

1. The calibration facility shall initiate contact with NIST and request a proficiency test for mammography calibrations.
2. NIST will conduct a proficiency test on an individual basis, as well as part of an accreditation program.
3. The proficiency test will consist of three stages. First NIST will calibrate a NIST transfer standard using two appropriate molybdenum and/or rhodium generated x-ray beam qualities. NIST will then send the transfer standard to the participating calibration facility, along with details of the NIST calibration conditions, excluding the calibration results. Calibrations of the NIST transfer chamber will be made at the facility using the appropriate beam qualities. The NIST transfer chamber shall be returned to NIST accompanied with the calibration results in the form of Gy/C, for each beam quality. Upon receipt of the chamber at NIST, it will be re-calibrated to assure stability and proper working conditions.
4. The results, provided by the participating facility, will be compared to the NIST calibrations. A NIST proficiency report will be issued to each participating calibration facility. The report will state the level of agreement with NIST under the conditions of the proficiency test. The proficiency test can be used to demonstrate that the participating facility can calibrate a NIST transfer standard, using techniques, characterized x-rays and NIST traceable instruments of sufficient quality permitting acceptable agreement with NIST. It will be the responsibility of the calibration facility to inform the FDA-MQSA of the proficiency test results.
5. The NIST mammography calibration facility will be used for all mammography calibrations and proficiency tests. It is the opinion of NIST that the molybdenum and rhodium generated x-ray beam qualities best represent the end users’ calibration conditions. Since medical physicists and inspectors are required to use NIST traceable instruments to conduct inspections of clinical molybdenum and/or rhodium anode x-ray units, the calibrations of the mammography calibration instruments will be conducted using two of the seventeen NIST Mo and/or Rh beam qualities. The selection of the two beam qualities to be used in the proficiency test will be made jointly by NIST and the participating calibration facility. The beam qualities chosen will be within the HVL and energy range of the beams available for calibrations at the participating facility. The facility may choose to compare with NIST for more than the two required beam qualities. Information concerning the air kerma rate, calibration distance and beam size used for the NIST calibrations will be issued to the participating calibration facility at the time of receipt of the NIST transfer standard. However, the calibration facility should use their routine calibration conditions for proficiency tests. The goal of the proficiency test is to test that the calibration facility is transferring quality calibrations under routine conditions.
6. NIST will conduct the proficiency test using a NIST-owned transfer-quality ionization chamber. The participating facility is responsible for obtaining the necessary electrometer. NIST will not provide a chamber/electrometer unit.
7. The proficiency test, which will consist of a test using a minimum of two beam qualities, will cost the same as two NIST calibrations plus 15 percent. If the calibration facility elects to be tested at more than two beam qualities, the cost will increase.

Inquiries or comments: michelle.obrien@nist.gov
Online: November 1998   -   Last update: March 2005