---
kind: "section"
citation: "10 C.F.R. § 35.635"
title: "10"
number: "35.635"
heading: "Full calibration measurements on gamma stereotactic radiosurgery units."
url: "https://uscodex.org/cfr/10/35.635"
---

# §35.635. Full calibration measurements on gamma stereotactic radiosurgery units.

- (a) A licensee authorized to use a gamma stereotactic radiosurgery unit for medical use shall perform full calibration measurements on each unit—
  - (1) Before the first medical use of the unit;
  - (2) **Before medical use under the following conditions—**
    - (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;
    - (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
  - (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)](#a) of this section, full calibration measurements must include determination of—
  - (1) The output within ±3 percent;
  - (2) Relative helmet factors;
  - (3) Isocenter coincidence;
  - (4) Timer accuracy and linearity over the range of use;
  - (5) On-off error;
  - (6) Trunnion centricity;
  - (7) Treatment table retraction mechanism, using backup battery power or hydraulic backups with the unit off;
  - (8) Helmet microswitches;
  - (9) Emergency timing circuits; and
  - (10) **Stereotactic frames and localizing devices (trunnions).**
- (c) A licensee shall use the dosimetry system described in [§ 35.630(a)](/cfr/10/35.630.md?p=a) to measure the output for one set of exposure conditions. The remaining radiation measurements required in [paragraph (b)(1)](#b-1) of this section may be made using a dosimetry system that indicates relative dose rates.
- (d) A licensee shall make full calibration measurements required by [paragraph (a)](#a) of this section in accordance with published protocols accepted by nationally recognized bodies.
- (e) A licensee shall mathematically correct the outputs determined in [paragraph (b)(1)](#b-1) of this section at intervals not exceeding 1 month for cobalt-60 and at intervals consistent with 1 percent physical decay for all other radionuclides.
- (f) Full calibration measurements required by [paragraph (a)](#a) of this section and physical decay corrections required by [paragraph (e)](#e) of this section must be performed by the authorized medical physicist.
- (g) A licensee shall retain a record of each calibration in accordance with [§ 35.2632](/cfr/10/35.2632.md).

## Notes

### Authority

Authority: Atomic Energy Act of 1954, secs. 81, 161, 181, 182, 183, 223, 234, 274 (42 U.S.C. 2111, 2201, 2231, 2232, 2233, 2273, 2282, 2021); Energy Reorganization Act of 1974, secs. 201, 206 (42 U.S.C. 5841, 5846); 44 U.S.C. 3504 note.

### Source

Source: 67 FR 20370, Apr. 24, 2002, unless otherwise noted.