TELETHERAPY UNITS; FULL CALIBRATION

Subpart 1. Calibration required. A licensee authorized to use a teletherapy unit for medical use must perform full calibration measurements on each teletherapy unit: A. before the first medical use of the unit; B. before medical use under the following conditions: (1) 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; (2) following replacement of the source or following reinstallation of the teletherapy unit in a new location; and (3) 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 C. at intervals not exceeding one year. Subp. 2. Required determinations. To satisfy subpart 1, full calibration measurements must include determination of: A. 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; B. the coincidence of the radiation field and the field indicated by the light beam localizing device; C. the uniformity of the radiation field and its dependence on the orientation of the useful beam; D. timer accuracy and linearity over the range of use; E. on-off error; and F. the accuracy of all distance-measuring and localization devices in medical use. Subp. 3. Required system. 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. Subp. 4. Required protocols. A licensee must make full calibration measurements required under subpart 1 according to published protocols accepted by nationally recognized bodies. Subp. 5. Required corrections. 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. Subp. 6. Authorized medical physicist. Full calibration measurements required under subpart 1 and physical decay corrections required under subpart 5 must be performed by the authorized medical physicist. Subp. 7. Record retention. A licensee must retain a record of each calibration according to part 4731.4518 .