Current through Register 1531, September 27, 2024
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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image
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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image
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.
