Section 11-45-121 - Computed tomography x-ray systems(a) General requirements: (1) Means shall be provided to terminate the x-ray exposure automatically by either de-energizing the x-ray source or shuttering the x-ray beam in the event of equipment failure affecting data collection. Such termination shall occur within an interval that limits the total scan time to no more than one hundred ten percent of its preset value through the use of either a backup timer or devices which monitor equipment function.(2) A visible signal shall indicate when the x-ray exposure has been terminated through the means required by paragraph (1).(3) The operator shall be able to terminate the x-ray exposure at any time during a scan, or series of scans under computed tomography x-ray system control, of greater than one-half second duration.(4) For any single tomogram system, means shall be provided to permit visual determination of the tomographic plane or a reference plane offset from the tomographic plane.(5) For any multiple tomogram system, means shall be provided to permit visual determination of the location of a reference plane. This reference plane can be offset from the location of the tomographic planes.(6) If a device using a light source is used to satisfy paragraphs (4) and (5), the light source shall provide illumination levels sufficient to permit visual determination of the location of the tomographic plane or reference plane under ambient light conditions of up to five hundred lux.(7) The computed tomography x-ray control and gantry shall provide visual indication whenever x-rays are produced and, if applicable, whether the shutter is open or closed.(8) Each emergency button or switch shall be clearly labeled as to its function.(9) The computed tomography x-ray system shall be designed such that the computed tomography conditions of operation to be used during a scan or a scan sequence shall be indicated before the initiation of a scan or a scan sequence. On equipment having all or some of these conditions of operation at fixed values, this requirement may be met by permanent markings. Indication of computed tomography conditions of operation shall be visible from any position from which scan initiation is possible.(10) When data are not being collected for image production, the radiation adjacent to the tube port shall not exceed that permitted by section 11-45-117(c).(11) The angular position where the maximum surface computed tomography dose index occurs shall be identified to allow for reproducible positioning of a computed tomography dosimetry phantom.(12) Additional requirements applicable to computed tomography x-ray systems containing a gantry manufactured after September 3, 1985: (A) The total error in the indicated location of the tomographic plane or reference plane shall not exceed five millimeters.(B) If the x-ray production period is less than one-half second, the indication of x-ray production shall be actuated for at least one-half second. Indicators at or near the gantry shall be discernible from any point external to the patient opening where insertion of any part of the human body into the primary beam is possible.(C) The deviation of indicated scan increment versus actual increment shall not exceed plus or minus one millimeter with any mass from zero to one hundred kilograms resting on the support device. The patient support device shall be incremented from a typical starting position to the maximum incremented distance or thirty centimeters, whichever is less, and then returned to the starting position. Measurement of actual versus indicated scan increment may be taken anywhere along this travel.(D) Premature termination of the x-ray exposure by the operator shall necessitate resetting of the computerized tomography conditions of operation before the initiation of another scan.(b) Provision shall be made for two-way aural communication between the patient and the operator at the control panel.(c) Viewing systems: (1) Windows, mirrors, closed-circuit television, or an equivalent shall be provided to permit continuous observation of the patient during irradiation and shall be so located that the operator can observe the patient from the control panel.(2) When the primary viewing system is by electronic means, an alternate viewing system (which may be electronic) shall be available for use in the event of failure of the primary viewing system.(d) Surveys: (1) All computed tomography x-ray systems installed after the effective date of these rules and those systems not previously surveyed shall have a survey made by, or under the direction of, a qualified medical physicist before use on human patients unless otherwise authorized by the director. In addition, such surveys shall be done after any change in the facility or equipment which might cause a significant increase in radiation hazard.(2) A written report of the survey shall be available for inspection by the department for three years.(e) Radiation calibrations: (1) Calibration of the radiation output of the computed tomography x-ray system shall be performed by, or under the direction of, a qualified medical physicist who is physically present at the facility during such calibration.(2) Calibration of a computed tomography x-ray system shall be performed at intervals specified by a qualified medical physicist and after any change or replacement of components which, in the opinion of the qualified medical physicist, could cause a change in the radiation output.(3) Calibration of the radiation output of a computed tomography x-ray system shall be performed with a calibrated dosimetry system. The calibration of such system shall be traceable to a national standard. The dosimetry system shall have been calibrated within the preceding two years.(4) Computed tomography dosimetry phantom(s) shall be used in determining the radiation output of a computed tomography x-ray system. Such phantom(s) shall meet the following specifications and conditions of use: (A) Computed tomography dosimetry phantom(s) shall be right circular cylinders of polymethyl methacrylate of density 1.19 plus or minus 0.01 grams per cubic centimeter. The phantom(s) shall be at least fourteen centimeters in length and shall have diameters of 32.0 centimeters for testing computed tomography x-ray systems designed to image any section of the body and 16.0 centimeters for systems designed to image the head or for whole body scanners operated in the head scanning mode.(B) Computed tomography dosimetry phantom(s) shall provide means for the placement of a dosimeter(s) along the axis of rotation and along a line parallel to the axis of rotation 1.0 centimeter from the outer surface and within the phantom. Means for the placement of dosimeters or alignment devices at other locations may be provided.(C) Any effects on the doses measured due to the removal of phantom material to accommodate dosimeters shall be accounted for through appropriate corrections to the reported data or included in the statement of maximum deviation for the values obtained using the phantom.(D) All dose measurements shall be performed with the computed tomography dosimetry phantom placed on the patient couch or support device without additional attenuation materials present.(5) Calibration shall be required for each type of head, body, or whole-body scan performed at the facility.(6) Calibration shall include the center multiple scan average dose and the surface multiple scan average dose.(7) Calibration procedures shall be in writing. Records of calibrations performed shall be maintained for inspection by the department for three years.(f) Spot checks shall be conducted: (1) Procedures shall be in writing and shall have been developed by a qualified medical physicist.(2) Procedures shall incorporate the use of a computed tomography dosimetry phantom which has a capability of providing an indication of contrast scale, noise, nominal tomographic section thickness, the resolution capability of the system for low and high contrast objects, and measuring the mean computed tomography number for water or other reference material.(3) Spot checks shall be included in the calibration required by subsection (e) and at time intervals and under system conditions specified by a qualified medical physicist.(4) Spot checks shall include acquisition of images obtained with the computed tomography dosimetry phantom(s) using the same processing mode and computed tomography conditions of operation as are used to perform calibrations required by subsection (e). The images shall be retained, until a new calibration is performed, in two forms as follows: (A) Photographic copies of the images obtained from the image display device; and(B) Images stored in digital form on a storage medium compatible with the computed tomography x-ray system.(5) Written records of the spot checks shall be maintained for inspection by the department for three years.(g) Operating procedures: (1) The computed tomography x-ray system shall be operated by an individual who has been specifically trained in its operation and licensed under chapter 11-44.(2) Information shall be available at the control panel regarding the operation and calibration of the system. Such information shall include the following:
(A) Dates of the latest calibration and spot checks and the location within the facility where the results of those tests may be obtained;(B) Instructions on the use of the computed tomography dosimetry phantom(s) including a schedule of spot checks appropriate for the system, allowable variations for the indicated parameters, and the results of at least the most recent spot checks conducted on the system;(C) The distance in millimeters between the tomographic plane and the reference plane if a reference plane is utilized; and(D) A current technique chart available at the control panel which specifies for each routine examination the computed tomography conditions of operation and the number of scans per examination.(3) If the calibration or spot check of the computed tomography x-ray system identifies that a system operating parameter has exceeded a tolerance established by the qualified medical physicist, use of the computed tomography x-ray system on patients shall be limited to those uses permitted by established written instructions of the qualified medical physicist.[Eff 11/12/99] (Auth: HRS §§ 321-10, 321-11, 321-71) (Imp: HRS §§ 321-1, 321-11(21), 321-71)