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Virginia Administrative Code
Title 12. Health
Agency 5. Department of Health
Chapter 481. Virginia Radiation Protection Regulations
10/21/2020

12VAC5-481-2045. Full Calibration Measurements.

A. Teletherapy units.

1. Licensees authorized to use a teletherapy unit for medical use shall 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 5.0% 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.

2. To satisfy the requirement of subdivision 1 of this subsection, full calibration measurements shall include determination of:

a. The output within plus or minus 3.0% 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.

3. Licensees shall use the dosimetry system described in 12VAC5-481-2044 to measure the output for one set of exposure conditions. The remaining radiation measurements required in subdivision 2 a of this subsection may be made using a dosimetry system that indicates relative dose rates.

4. Licensees shall make full calibration measurements required by subdivision 1 of this subsection in accordance with published protocols accepted by nationally recognized bodies.

5. Licensees shall mathematically correct the outputs determined in subdivision 2 a of this subsection for physical decay for intervals not exceeding one month for cobalt-60, six months for cesium-137, or at intervals consistent with 1.0% decay for all other nuclides.

6. Full calibration measurements required by subdivision 1 of this subsection and physical decay corrections required by subdivision 5 of this subsection shall be performed by the authorized medical physicist (AMP).

B. Remote afterloader units.

1. Licensees authorized to use a remote afterloader unit for medical use shall 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) Following replacement of the source or following reinstallation of the unit in a new location outside the facility; and

(2) Following any repair of the unit that includes removal of the source or major repair of the components associated with the source exposure assembly;

c. At intervals not exceeding one quarter for high dose-rate, medium dose-rate, and pulsed dose-rate remote afterloader units with sources whose half-life exceeds 75 days; and

d. At intervals not exceeding one year for low dose-rate remote afterloader units.

2. To satisfy the requirement of subdivision 1 of this subsection, full calibration measurements shall include, as applicable, determination of:

a. The output within plus or minus 5.0%;

b. Source positioning accuracy to within plus or minus 1 millimeter;

c. Source retraction with backup battery upon power failure;

d. Length of the source transfer tubes;

e. Timer accuracy and linearity over the typical range of use;

f. Length of the applicators; and

g. Function of the source transfer tubes, applicators, and transfer tube-applicator interfaces.

3. Licensees shall use the dosimetry system described in 12VAC5-481-2044 to measure the output.

4. Licensees shall make full calibration measurements required by subdivision 1 of this subsection in accordance with published protocols accepted by nationally recognized bodies.

5. In addition to the requirements for full calibrations for low dose-rate remote afterloader units in subdivision 2 of this subsection, licensees shall perform an autoradiograph of the sources to verify inventory and source arrangement at intervals not exceeding one calendar quarter.

6. For low dose-rate remote afterloader units, licensees may use measurements provided by the source manufacturer that are made in accordance with subdivisions 1 through 5 of this subsection.

7. Licensees shall mathematically correct the outputs determined in subdivision 2 a of this subsection for physical decay at intervals consistent with 1.0% physical decay.

8. Full calibration measurements required by subdivision 1 of this subsection and physical decay corrections required by subdivision 7 of this subsection shall be performed by the AMP.

C. Gamma stereotactic radiosurgery units.

1. Licensees authorized to use a gamma stereotactic radiosurgery unit for medical use shall 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 5.0% from the output obtained at the last full calibration corrected mathematically for radioactive decay;

(2) Following replacement of the sources or following reinstallation 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, 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.

2. To satisfy the requirement of subdivision 1 of this subsection, full calibration measurements shall include determination of:

a. The output within plus or minus 3.0%;

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 localizing devices (trunnions).

3. Licensees shall use the dosimetry system described in 12VAC5-481-2044 to measure the output for one set of exposure conditions. The remaining radiation measurements required in subdivision 2 a of this subsection may be made using a dosimetry system that indicates relative dose rates.

4. Licensees shall make full calibration measurements required by subdivision 1 of this subsection in accordance with published protocols accepted by nationally recognized bodies.

5. Licensees shall mathematically correct the outputs determined in subdivision 2 a of this subsection at intervals not exceeding one month for cobalt-60 and at intervals consistent with 1.0% physical decay for all other radionuclides.

6. Full calibration measurements required by subdivision 1 of this subsection and physical decay corrections required by subdivision 5 of this subsection shall be performed by the AMP.

Statutory Authority

§ 32.1-229 of the Code of Virginia.

Historical Notes

Derived from Volume 32, Issue 24, eff. August 25, 2016.

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