NAC459.592. Therapeutic X-ray systems: Surveys; calibration; operating procedures.

     1. All new facilities and existing facilities not previously surveyed must have a radiation protection survey made by, or under the direction of, a qualified expert. This survey must also be done after any change in the facility which might produce a radiation hazard. The expert shall report his or her findings, in writing, to the person in charge of the facility and a copy of the report must be transmitted by the registrant to the Division within 30 days.

     2. The radiation output of each therapeutic X-ray machine must be calibrated by, or under the direction of, a qualified expert who is physically present at the facility during the calibration procedure. The calibration must be repeated after any change in, or replacement of, components of the X-ray generating equipment which could cause a change in X-ray output. Calibration of the therapy beam must be performed with a measuring instrument the calibration of which is directly traceable to national standards of exposure or absorbed dose and which has been calibrated within the preceding year. Records of the calibrations must be provided to and maintained by the registrant. In addition:

     (a) Each therapeutic X-ray machine must have the calibrations repeated at time intervals not exceeding 1 year. The calibration must include at least the following determinations:

          (1) The accurate determination of the air dose rate or the dose rate in a suitable phantom, as appropriate, for a sufficient number of operating parameters for each effective energy to permit the determination of the dose received by the patient;

          (2) Verification that the equipment is operating in accordance with the design specifications concerning the congruence between the radiation field and light localizer, when a localizer is used, and for beam flatness and symmetry at the specified depths;

          (3) The effective energy, for example, half-value layer when appropriate, for every combination of kVp and filter used for radiation therapy;

          (4) The uniformity of the radiation field and its dependence upon the direction of the useful beam; and

          (5) The calibration determinations must be provided in sufficient detail so that the absorbed dose in rads to tissue adjacent to, as well as in the useful beam, may be calculated to within ±5 percent of the intended absorbed dose.

     (b) Therapeutic X-ray systems capable of operation at greater than 150 kVp must, in addition to the annual calibration required in paragraph (a) have spot checks performed which meet the following criteria:

          (1) A spot check must be made at least monthly or after 50 operating hours, whichever is shorter, and must include carefully selected representative or indicative measurements which will demonstrate the consistency of relevant machine operating characteristics or the lack of such characteristics.

          (2) The spot-check methods must be in writing and have been designed by a qualified expert. Spot checks must include verification of continued congruency between the radiation field and localizing device where an optical field illuminator is used.

          (3) Spot checks which are erratic or inconsistent with calibration data must be investigated promptly.

          (4) For machines in which beam quality may vary significantly, spot checks must include beam quality checks.

          (5) Whenever a spot check indicates a significant change, as specified in the qualified expert’s spot check design, in the operating characteristics of a machine, the machine must be recalibrated as required in paragraph (a).

          (6) A log must be kept of all spot-check measurements.

     (c) In the therapeutic application of X-ray equipment constructed with beryllium or other low-filtration windows, the registrant must ensure that the unfiltered radiation reaches only the part intended and that the useful beam port is blocked at all times except when actually being used.

     (d) Therapeutic X-ray machines must not be left unattended unless the locking device, required by paragraph (e) of subsection 4 of NAC 459.588, is set to prevent activation of the useful beam.

     (e) Except as provided in paragraph (f) of subsection 4 of NAC 459.554, no person other than the patient may be in the treatment room during exposures unless he or she is protected by a barrier sufficient to meet the requirements of NAC 459.325, and no person other than the patient may be in the treatment room when the kVp exceeds 150 during exposures except in emergency situations.

     (f) The tube housing assembly must not be held by anyone during exposures.

     (g) When a patient must be held in position for radiation therapy, mechanical restraining devices must be used.

     [Bd. of Health, Radiation Control Reg. §§ 6.8.3-6.8.3.2.7, eff. 2-28-80]—(NAC A 1-18-94)