Okla. Admin. Code § 310:281-11-15

Current through Vol. 42, No. 6, December 2, 2024

Section 310:281-11-15 - Computed tomography x-ray systems

(a)System requirements.

(1)Tomographic plane indication and alignment.

(A) 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.

(B) For any multiple tomogram system, means shall be provided to permit visual determination of the location of a reference plane. The reference plane can be offset from the location of the tomographic planes.

(C) If a device using a light source is used to satisfy 310:281-11-15(a)(1)(A) or (B), 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 500 lux.

(2)Indication of CT conditions of operation. The CT x- ray system shall be designed such that the CT conditions of operation to be used during a scan or a scan sequence are indicated prior to the initiation of a scan or a scan sequence. On a system having all or some of these conditions of operation at fixed values, this requirement may be met by permanent markings. Indication of CT conditions of operation shall be visible from any position from which scan initiation is possible.

(3)Initiation of operation.

(A) The x-ray control and gantry shall provide visual indication whenever x-rays are produced and, if applicable, whether the shutter is open or closed.

(B) Means shall be provided to require operator initiation of each individual scan or series of scans.

(C) All emergency buttons/switches shall be clearly labeled as to their functions.

(4)Termination of exposure.

(A) 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 the equipment failure affecting data collection. Such termination shall occur within an interval that limits the total scan time to no more than 110 percent of its preset value through the use of either a backup timer or devices which monitor equipment function.

(B) A visible signal shall indicate when the x-ray exposure has been terminated through the means required by 310:281-11-15(a)(4)(A).

(C) The operator shall be able to terminate the x-ray exposure at any time during a scan, or series of scans under x-ray system control, of greater than 0.5 second duration. Termination of the x-ray exposure shall necessitate resetting of the CT conditions of operation prior to initiation of another scan.

(5)Extraneous radiation. The system shall perform such that the radiation produced adjacent to the tube housing assembly, including the tube port, during periods of time that scans are not being performed does not exceed the levels permitted by 310:281-11-12(c).

(6)Additional requirements applicable to CT 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 5 millimeters.

(B) If the x-ray production period is less than 0.5 second, the indication of x-ray production shall be activated for at least 0.5 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 to within 1 millimeter with any mass from O to 100 kilograms resting on the support device. The patient support device shall be incremented from a typical starting position to the maximum incremented distance or 30 centimeters, whichever is less, and then returned to the starting position. Measurement of actual versus indicated scan increment can be taken anywhere along this travel.

(D) Premature termination of the x-ray exposure by the operator shall necessitate resetting of the CT conditions of operation prior to the initiation of another scan.

(7)Maximum surface CTDI identification. The angular position where the maximum surface CTDI occurs shall be identified to allow for reproducible positioning of a CT dosimetry phantom.

(b)Facility design requirements.

(1)Aural communication. Provision shall be made for two-way aural communication between the patient and the operator at the control panel.

(2)Viewing systems.

(A) Windows, mirrors, closed-circuit television, or an equivalent shall be provided to permit continuous observation of the patient during irradiation and positioned to allow the operator to observe the patient from the control panel.

(B) 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.

(c)Surveys, dose measurements, spot checks, operating procedures, and preventative maintenance services.

(1)Surveys.

(A) All CT systems shall have a survey made by or under the direct supervision of a medical physicist.

(i) All dental cone beam CTs under 120 kVp are exempt from this requirement; and

(ii) CT systems not used for diagnostic purposes are exempt from this requirement.

(B) Performance surveys by a medical physicist shall be made:

(i) at intervals not to exceed 1 year;

(ii) when major maintenance, except x-ray tube replacement, that could affect radiation output is performed; and

(iii) when a major change in the systems operation is accomplished; for example, introduction of a new software package.

(C) The permittee shall obtain a written report of the survey from the medical physicist and a copy of the report shall be made available to the Department upon request.

(2)Dose measurements.

(A) The dose measurements of the radiation output of the CT system will be done by a medical physicist. Dose limits for adult head, adult abdomen, and pediatric abdomen are listed in 310:281-11-5.

(B) Any calibration or recalibration on a CT system required by the medical physicist's survey shall be done by a qualified service representative. Any work deemed necessary by the permittee, other than that permitted by the manufactures' operators manual, shall be performed by a qualified service representative.

(C) Calibration of the dose measurements of a CT system is required for each type of head, body, or whole-body scan performed at the facility.

(D) Dose measurements shall meet the following requirements:

(i) The dose profile along the center axis of the CT phantom for the minimum, maximum, and midrange values of the nominal tomographic section thickness used by the permittee shall be measurable. Where less than 3 nominal tomographic thicknesses can be selected, the dose profile determination shall be performed for each available nominal tomographic section thickness.

(ii) The CTDI along the two axes specified in 310:281-11-15(c)(3)(A)(ii) shall be measured. The CT dosimetry phantom shall be oriented so that the measurement point 1.0 centimeter from the outer surface and within the phantom is in the same angular position within the gantry as the point of maximum surface CTDI identified. The CT conditions of operation shall correspond to typical values used by the permittee.

(E) Calibration of the dose measurements of a CT equipment shall be performed with a calibrated dosimetry system.

(i) Calibration of such a system shall be traceable to the national standard. The dosimetry system shall have been calibrated within the preceding 2 years.

(ii) Calibration procedures of the dosimetry system shall be in writing. Records of calibration performed shall be available for inspection by the Department.

(3)CT dosimetry phantom(s). CT dosimetry phantom(s)shall be used in determining the radiation output of CT systems. Such phantom(s) shall meet the following specifications and conditions of use:

(A) CT dosimetry phantom(s) shall be made of a material analogous to human tissue. (Water and acrylic are acceptable). If they are made of acrylic, they should have a density of 1.19 plus or minus 0.01 grams per cubic centimeter. The phantom(s) shall be at least 14 centimeters in length and have a diameter of 32.0 centimeters for testing CT systems designed to image any section of the body and 16.0 centimeters for equipment designed to image the head or for whole body equipment operated in the head scanning mode.

(B) CT dosimetry phantoms shall provide a means for the placement of a dosimeter(s) along the axis of rotation and a line parallel to the axis of rotation 1.0 centimeter from the outer surface and within the phantom. Means for the placement of dosimeter or alignment devices at other locations should 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 CT phantom placed on the patient couch or support devices without additional attenuation materials present.

(E) If contrast studies are done, the materials used should be made of water, acrylic, polyethelene, and air. They will be used to simulate bone and different types of tissue.

(4)Spot checks.

(A) Spot check procedures shall be developed by a medical physicist.

(B) All spot checks shall be included in the medical physicist survey required by 310:281-11-15(c)(2), and otherwise at time intervals and under equipment conditions specified by a medical physicist.

(C) Spot checks shall include acquisition of images obtained with the CT dosimetry phantom(s) using the same processing mode and CT conditions of operation as are used to perform dose measurements required by 310:281-11-15(c)(2). The images shall be retained, until a new dose measurement is performed, in two forms as follows:

(i) photographic copies of the images obtained from the image display device; and

(ii) images stored in digital form of the most recent spot check on a storage medium compatible with the CT x-ray system.

(D) Written records of the spot checks performed shall be maintained for inspection by the Department.

(5)Operating procedures.

(A) The CT system shall not be operated except by an individual who has been specifically trained in its operation. Documentation of this training must be available upon request of the Department inspector.

(B) Information shall be available at the control panel regarding the operation and calibration of the system. Such information shall include the following.

(i) Dates of the latest survey, preventative maintenance service, spot checks, and location within the facility of where to find the results of those tests;

(ii) Instructions on the use of the CT 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;

(iii) The distance in millimeters between the tomographic plane and the reference plane if a reference plane is utilized; and

(iv) A current technique chart available at the control panel which specifies, each routine examination, the CT conditions of operation, and the number of scans per examination.

(C) If the medical physicist survey or spot checks of the CT system identifies that a systems operating parameter(s) has exceeded a tolerance established by the medical physicist, use of the CT equipment on patients shall be limited to those uses permitted by established written instructions of the medical physicist.

(6)Preventative maintenance services. Each permittee shall establish a preventative maintenance schedule where their CT system is serviced at least once every 3 months by a qualified service representative.

Okla. Admin. Code § 310:281-11-15

Added at 8 Ok Reg 3503, eff 8-15-91 (emergency); Added at 9 Ok Reg 1643, eff 5-29-92; Amended at 21 Ok Reg 1037, eff 5-13-04

Amended by Oklahoma Register, Volume 38, Issue 24, September 1, 2021, eff. 9/11/2021