(a) A licensee authorized to use a gamma stereotactic radiosurgery unit for medical use shall perform full calibration measurements on each unit—

1. (1) Before the first medical use of the unit;

2. (2) Before medical use under the following conditions—

   1. (i) Whenever spot-check measurements indicate that the output differs by more than 5 percent from the output obtained at the last full calibration corrected mathematically for radioactive decay;
   2. (ii) Following replacement of the sources or following reinstallation of the gamma stereotactic radiosurgery unit in a new location; and
   3. (iii) 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
3. (3) At intervals not exceeding 1 year, with the exception that relative helmet factors need only be determined before the first medical use of a helmet and following any damage to a helmet.

(b) To satisfy the requirement of paragraph (a) of this section, full calibration measurements must include determination of—

1. (1) The output within ±3 percent;
2. (2) Relative helmet factors;
3. (3) Isocenter coincidence;
4. (4) Timer accuracy and linearity over the range of use;
5. (5) On-off error;
6. (6) Trunnion centricity;
7. (7) Treatment table retraction mechanism, using backup battery power or hydraulic backups with the unit off;
8. (8) Helmet microswitches;
9. (9) Emergency timing circuits; and
10. (10) Stereotactic frames and localizing devices (trunnions).