When the mammography unit with a light beam that passes through the collimator is initially placed in service, the medical physicist must perform the light beam test as part of the mammography equipment evaluation. This test should also be performed periodically throughout the life of the unit or when an old bulb is replaced with a new one. Periodic testing and testing of a new bulb may be done by a radiologic technologist, repair person, or other qualified person but should be performed in consultation with the medical physicist.
The frequency of periodic testing should be established with reference to the manufacturer’s maintenance specifications and the use considerations (wear and tear) unique to the facility. If the light beam fails during a mammography equipment evaluation, it must be repaired before the light beam is used on patients. If the facility identifies the problem at any other time, it should be repaired as soon as possible.
Manufacturers may specify procedures and frequency for testing the light illuminance in their maintenance instructions and adherence to these recommendations should normally be adequate; however, the responsibility for compliance still remains with the facility.
Some recommended testing specifications for the average illuminance are found in 21 CFR 1020.31(d)(2)(ii), where it states "The average illuminance shall be based upon the measurements made in the approximate center of each quadrant of the light field." The test must be conducted at the maximal SID or one meter, whichever is less, and should compensate for the ambient light usually present during clinical examinations. Instrumentation used should be appropriate for the purpose. Since this might require special test equipment not usually available in the facility, FDA suggests that the facility add it to the list of items to be examined by the physicist during the annual physics survey.