A licensee authorized to use a teletherapy unit for medical use must perform full calibration measurements on each teletherapy unit:
before medical use under the following conditions:
whenever spot check measurements indicate that the output differs by more than five percent from the output obtained at the last full calibration corrected mathematically for radioactive decay;
following replacement of the source or following reinstallation of the teletherapy unit in a new location; and
following any repair of the teletherapy unit that includes removal of the source or major repair of the components associated with the source exposure assembly; and
To satisfy subpart 1, full calibration measurements must include determination of:
the output within plus or minus three percent for the range of field sizes and for the distance or range of distances used for medical use;
the coincidence of the radiation field and the field indicated by the light beam localizing device;
the uniformity of the radiation field and its dependence on the orientation of the useful beam;
A licensee must use the dosimetry system described in part 4731.4468, subpart 1, to measure the output for one set of exposure conditions. The remaining radiation measurements required under subpart 2 may be made using a dosimetry system that indicates relative dose rates.
A licensee must make full calibration measurements required under subpart 1 according to published protocols accepted by nationally recognized bodies.
A licensee must mathematically correct the outputs determined in subpart 2, item A, for physical decay for intervals not exceeding one month for cobalt-60, six months for cesium-137, or at intervals consistent with one percent decay for all other nuclides.
Full calibration measurements required under subpart 1 and physical decay corrections required under subpart 5 must be performed by the authorized medical physicist.
29 SR 755
March 12, 2009
Official Publication of the State of Minnesota
Revisor of Statutes