GAMMA STEREOTACTIC RADIOSURGERY UNITS; FULL CALIBRATION

Subpart 1. Calibration required. A licensee authorized to use a gamma stereotactic radiosurgery unit for medical use must perform full calibration measurements on each 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 sources or following reinstallations of the gamma stereotactic radiosurgery unit in a new location; and (3) following any repair of the gamma stereotactic radiosurgery unit that includes removal of the sources or major repair of the components associated with the source assembly; and C. at intervals not exceeding one year, except that relative helmet factors need only be determined before the first medical use of a helmet and following any damage to a helmet. Subp. 2. Required determinations. To satisfy subpart 1, full calibration measurements must include determination of: A. the output within plus or minus three percent; B. relative helmet factors; C. isocenter coincidence; D. timer accuracy and linearity over the range of use; E. on-off error; F. trunnion centricity; G. treatment table retraction mechanism, using backup battery power or hydraulic backups with the unit off; H. helmet microswitches; I. emergency timing circuits; and J. stereotactic frames and localization devices (trunnions). 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 under subpart 2, item A, at intervals not exceeding one month for cobalt-60 and at intervals consistent with one percent physical decay for all other radionuclides. 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 .