Any facility offering CT services after April 30, 2011 shall have ACR accreditation.
Definitions. In addition to the definitions provided in 105 CMR 120.402, the following definitions shall be applicable
Computed Tomography Dose Index (CTDI) means the integral of the dose profile along a line perpendicular to the tomographic plane divided by the product of the nominal tomographic section thickness and the number of tomograms produced in a single scan, that is:
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where:
z = Position along a line perpendicular to the tomographic plane;
D(z) = Dose at position z;
T = Nominal tomographic section thickness;
n = Number of tomograms produced in a single scan.
Computed Tomography Dose Index (CTDI) assumes that the dose profile is centered around z=0 and that, for a multiple tomogram system, the scan increment between adjacent scans is nT.
CT Dosimetry Phantom means the phantom used for determination of the dose delivered by a CT x-ray system. The phantom shall be a right circular cylinder of polymethl-methacrylate of density 1.19±0.01 grams per cubic centimeter. The phantom shall be at least 14 centimeters in length and shall have diameters of 32.0 centimeters for testing any CT system designed to image any section of the body (whole body scanners) and 16.0 centimeters for any system designed to image the head (head scanners) or for any whole body scanner operated in the head scanning mode. The phantom shall provide means for the placement of a dosimeter(s) along its 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 a dosimeter(s) or alignment device at other locations may be provided for convenience. Any effect 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.
Dose Profile means the dose as a function of position along a line.
Modulation Transfer Function means the modulus of the Fourier transform of the impulse response of the system.
Noise means the standard deviation of the fluctuations in CTN expressed as a percentage of the attenuation coefficient of water. Its estimate (Sn) is calculated using the following expression:
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where:
CS = Linear attenuation coefficient of the material of interest.
µw = Linear attenuation coefficient of water.
= Standard deviation of the CTN of picture elements in a specified area of the CT image.
Picture Element means an elemental area of a tomogram.
Remanufacturing means modifying a CT system in such a way that the resulting dose and imaging performance become substantially equivalent to any CT x-ray system manufactured by the original manufacturer on or after November 29, 1984. Any reference in 105 CMR 120.408 to manufacture, manufacturer, or manufacturing includes remanufacture, Remanufacturing, respectively.
Sensitivity Profile means the relative response of the CT x-ray system as a function of position along a line perpendicular to the tomographic plane.
Single Tomogram System means a CT x-ray system which obtains x-ray transmission data during a scan to produce a single tomogram.
(A)Equipment 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 105 CMR 120.409(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 equipment 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 equipment failure affecting data collection. Such termination shall occur within an interval that limits the total scan time to no more than 110% 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 105 CMR 120.409(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 105 CMR 120.404(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 five millimeters.(b) If the x-ray production period is less than 0.5 second, the indication of x-ray production shall be actuated for at least 0.5 seconds. 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 one millimeter with any mass from zero 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.(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 System.(a) 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.(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)Dose Measurements, Spot Checks, Surveys, and Calibrations. (1)Dose Measurements.(a) Dose measurements of the radiation output of the CT x-ray system shall be performed by a qualified medical physicist.(b) Dose measurements of a CT 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 a qualified medical physicist, could cause a change in the radiation output.(c) Measurements of the radiation output of a CT x-ray system shall be performed with a calibrated dosimetry system. The dosimetry system shall have been calibrated or inter compared with a calibrated chamber within the preceding two years. The calibration of such system shall be traceable to a national standard.(d) Calibration procedures shall be in writing. Records of calibration performed shall be maintained for inspection by the Radiation Control Program.(2)Spot Checks. (a) Spot check procedures shall be in writing and developed by a qualified medical physicist.(b) All spot checks shall be included in the calibration required by 105 CMR 120.409(C)(1), and otherwise at time intervals and system conditions specified by a qualified medical physicist.(c) Spot checks shall include acquisition of images obtained with the phantoms using the same processing mode and CT conditions of operation as are used to perform dose measurements required by 105 CMR 120.409(C)(1). The images shall be retained until a new dose measurement is performed in two forms as follow: 1. Photographic copies of the images obtained from the image display device; and 2. Images stored in digital form of the most recent spot check on a storage medium compatible with the CT x-ray system.(d) The spot-check procedures shall incorporate the use of a CT 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 CTN for water or other reference material.(e) Written records of the spot checks performed shall be maintained for inspection by the Agency.(3)Surveys.(a) All CT x-ray systems installed after March 3, 2012 and those systems not previously surveyed shall have a survey made by a qualified medical physicist. In addition, such surveys shall be done after any change in the facility or equipment which might cause a significant increase in radiation hazard.(b) The registrant of the facility [licensee] shall obtain a written report of the survey from the qualified medical physicist, and a copy of the report shall be made available to the Agency upon request.(4)Physics Evaluations.(a) The physics evaluation of the radiation output of the CT x-ray system shall be performed by a qualified medical physicist.(b) The physics evaluation of a CT x-ray system shall be performed after initial installation and before use on human patients, annually or 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.(c) The physics evaluation of the radiation output of a CT x-ray system shall be performed with a calibrated dosimetry system. The physics evaluation of such system shall be traceable to a national standard. The dosimetry system shall have been calibrated within the preceding two years.(d) CT dosimetry phantom(s) shall be used in determining the radiation output of a CT x-ray system. Such phantom(s) shall meet the following specifications and conditions of use:1. CT 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 14 centimeters in length and shall have diameters of 32.0 centimeters for testing CT 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;2. CT 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;3. 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;4. All dose measurements shall be performed with the CT dosimetry phantom placed on the patient couch or support device without additional attenuation materials present.(e) The physics evaluation shall be required for each type of head, body, or whole-body scan performed at the facility.(f) Physics evaluation shall meet the following requirements: 1. The dose profile along the center axis of the CT dosimetry phantom for the minimum, maximum, and midrange values of the nominal tomographic section thickness used by the registrant shall be measurable. Where less than three nominal tomographic thicknesses can be selected, the dose profile determination shall be performed for each available nominal tomographic section thickness;2. The CTDi2 along the two axes specified in 105 CMR 120.409(C)(4)(d)2. 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 registrant.3. The spot checks specified in 105 CMR 120.409(C)(2) shall be made.(D)Additional Operational Controls for CT X-Ray Systems. (1) The CT x-ray system shall only be operated by an individual who has been specifically trained in its operation and who holds a valid Massachusetts license in radiologic technology. (2) Information shall be available at the control panel or in a specified location regarding the operation and calibration of the system. The information shall contain:(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) The results of at least the most recent checks conducted on the system; and,(c) The distance, in millimeters, between the tomographic plane and the reference plane, if a reference plane is utilized.(3) If the calibration or spot check of the CT x-ray system identifies that a system operating parameter has exceeded a tolerance established by the qualified medical physicist, use of the CT x-ray system on patients shall be limited to those uses permitted by established written instructions of the qualified medical physicist.(4) Quarterly reviews shall be conducted of dose protocols being used at the facility.(5) Dose indicators shall be included in the patient's medical record.(E)Mini CT Units. (1) All facilities that use a Mini CT unit shall follow the manufacturer's recommendations for Quality Control.(2) Operators of Mini CT units shall be: (a) Licensed physician; or(b) Licensed as a Radiologic Technologist.(3) Each facility shall maintain the records of applications from the manufacturer.