180 NAC 7-075. FULL CALIBRATION MEASUREMENTS ON GAMMA STEREOTACTIC RADIOSURGERY UNITS

075. FULL CALIBRATION MEASUREMENTS ON GAMMA STEREOTACTIC RADIOSURGERY UNITS. 075.01 FREQUENCY. 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: (i) Whenever spot-check measurements indicate that the output differs by plus or minus 5% from the output obtained at the last full calibration corrected mathematically for radioactive decay;(ii) Following replacement of the sources or following reinstallation of the gamma stereotactic radiosurgery unit in a new location; and(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 (C) At intervals not exceeding one 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. 075.02 DETERMINANTS. To satisfy the requirement of 180 NAC 7-075.01, full calibration measurements must include determination of: (A) The output within ±3%;(B) Relative helmet factors to verify that the helmet material provides the required shielding to the patient;(C) Isocenter coincidence to confirm the centering accuracy of the radiation beam relative to the alignment helmet openings;(D) Timer accuracy and linearity over the range of use;(E) On-off error;(F) Trunnion centricity to determine the rotational center of the source relative to the alignment helmet openings;(G) Treatment table retraction mechanism, using backup battery power or hydraulic backups with the unit off;(H) Helmet microswitches to determine if the switches terminate the radiation beam;(I) Emergency timing circuits; and(J) Stereotactic frames, localizing devices and trunnions. 075.03 DOSIMETRY SYSTEM. A licensee must use the dosimetry system described in 180 NAC 7-072.01 to measure the output for one set of exposure conditions. The remaining radiation measurements required in paragraph 180 NAC 7-075.02(A) may be made using a dosimetry system that indicates relative dose rates. 075.04 CALIBRATION MEASUREMENT PROTOCOLS. A licensee must make full calibration measurements required by 180 NAC 7-075.01 according to published protocols accepted by nationally recognized bodies. 075.05 MATHEMATICAL CORRECTION OF OUTPUTS. A licensee must mathematically correct the outputs determined in 180 NAC 7-075.02(A) at intervals not exceeding one month for cobalt-60 and at intervals consistent with one percent physical decay for all other radionuclides. 075.06 AUTHORIZED MEDICAL PHYSICIST. Full calibration measurements required by 180 NAC 7-075.01 and physical decay corrections required by 180 NAC 7-075.05 must be performed by the authorized medical physicist. 075.07 RECORDS. A licensee must retain a record of each calibration according to 180 NAC 7-108.