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1. IntheNameo
Go

2. Radiation Protection
in CT
Seyedeh Shokoofeh Mousavi Gazafroudi
Seyedeh Shabnam Mousavi Gazafroudi
2

3. Table of Content
Introduction to radiation
protection
Review of CT
Radiation protection in CT
Equipment & layout of room
Principles & guidelines
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4. Introduction to Radiation
Protection

5. Radiation risk
Risk is proportional to absorbed dose
Risk is quantified by determining the “effective
dose” and is expressed as millisievert (mSv)
Atomic bomb survivors who experienced doses
that were slightly higher than doses encountered
in CT demonstrated increased cancers.
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Sciences
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8. Isfahan University of Medical Sciences
ALARA policy
The goal of the radiation safety program is to ensure
that radiation dose to workers, members of the public,
and to the environment is as low as reasonably
achievable (ALARA) below the limits established by
regulatory agencies.
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9. Factors in radiation protection
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10. Isfahan University of Medical Sciences
Principles of radiological
protection
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11. Review of CT

12. Isfahan University of Medical Sciences
CT examination
"Computed tomography (CT)" means the production of a tomogram by
the acquisition and computer processing of x-ray transmission data.
Computed tomography includes the capability of producing axial
tomograms.
CT examination is a “high dose” procedure and Justification in CT is of
particular importance for RP.
The absorbed dose to tissues from CT can often approach or exceed the
levels known to increase the probability of cancer as shown in
epidemiological studies.

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15. 12/17/17
Radiation Protection in
CT

16. Justification in CT
A series of clinical factors play a special part in justification:
Adequate clinical information, including the records of
previous imaging investigations, must be available
In certain applications prior investigation of the patient
by alternative imaging techniques might be required
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Optimization in CT
Optimal use of ionizing radiation involves the
interplay of the imaging process:
the diagnostic quality of the CT image
the radiation dose to the patient
the choice of radiological technique
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18. Patient dose in CT
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These
parameters
affect on
patient
absorbed dose :

19. Isfahan University of Medical Sciences
Patient dose in CT
mAs ( directly proportional to radiation dose)
KVp ( inversely but not linearly proportional to dose)
Pitch (inversely related to dosage)
Slice thickness (requires an increase in mAs)
Number of scans (doubling the radiation dose)
Scan time (faster scans lead to an increased scan area)
Scanning mode (step-based vs.spiral technique, single-slice vs.
multi-slice)

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21. Equipment & layout of
room

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Stationary CT rooms
Computed
tomography rooms
typically have high
workloads and high
voltage
kilo
technique settings. operator
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Room layout
The official UK guidance on the design of radiological
facilities suggests that CT x-ray rooms should be designed
to a minimum dimension of 38 m².
at least 1/16-Inch lead shielding or equivalent is required for
the walls, doors, floors, ceilings, and operator's barrier. The
concrete equivalence would be about 4 to 6 inches of
standard-density concrete , depending on workload and
distance
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Equipment & facilities
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Equipment & facilities
Protective apron, glasses, gloves, collar & gonad shields and
of course film badge & other dosimeter should be used.
All of devices should be certificated and calibrated.
Radiation safety committee and specially medical physicist
have important role in performing
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Medical physicist’s tasks
Facilities shall be established and implemented under the
supervision of the medical physicist (MP)
MP must perform an initial or acceptance test of each CT system
prior to use on patients
MP must perform an annual evaluation of the CT system and
quality control program
Facility conducts a continuous quality control program
designed/overseen by the MP

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28. Principles &
Guidelines

29. ICRP recommendations to reduce
personnel dose
Personal dosimeter shall be monitored (worn properly, read
at an appropriate frequency)
Personal protective equipment to all staff should be available
Protective clothing should be worn by staff
Duration of exposures, dose-rate and X-ray field size should
be minimized
Positioning of personnel during examinations should be
assessed

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31. ICRP recommendations
to reduce patient dose
Actions for 3 groups are defined:
Operator
Manufacture
Physicians
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What can operators do?
Limit the scanned volume
Reduce mAs values
Use automatic exposure control
Shielding of superficial organs
Use of spiral CT with pitch factor>1
Separate factors for children
Use of partial rotation
Adequate selection of image reconstruction parameters
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33. Isfahan University of Medical Sciences
Actions for manufacturers
Introduce automatic exposure control
Be conscious of high doses in CT
Include safety features to avoid unnecessary dose
Display of dose
Convenience in using low dose protocols
Draw attention of users to selecting separate protocols for
paediatric patients
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Actions for physician
Ensure that patients are not irradiated unjustifiably
Clinical guidelines advising which examinations are appropriate and
acceptable should be available
Consider whether the required information be obtained by MRI,
ultrasonography
Consider value of contrast medium enhancement
Clinician has the responsibility to communicate to the radiologist about
previous CT examination
CT examination of chest in young girls and young females needs to be
justified in view of high breast dose
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General rules in x-ray departments
Using film badge & regular periodic dosimetry
Using standard devices , testing them periodically, keeping
according to manufacture order.
Applying protective equipment for all of patient
Training technologists in order to proper usage of imaging
machines & protective equipments
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Special rules in CT departments
Use of low dose scanning protocol
Warm up , calibration & check up of CT machines result in patient
dose reduction
CT technologist should assess patient information and then choose
best technique according to indication, size and location of lesions
Accurate selection of slice tilt specially in brain scan
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37. AEOI recommendations
Atomic Energy Organization of Iran (AEOI) publishes guidelines
and reports periodically
latest guideline consists of 6 chapter about rules for radiation
activities in diagnostic departments
objectives, applications, key words definitions, and
responsibilities are mentioned in introduction of named report.
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AEOI report INRARP6CP02 ( Chapter 3 )
Choose technical factors to acquire acceptable quality images and
low dose to patient
Use minimum slice number and minimum mAs according to
clinical goals
Don’t perform pre contrast scan routinely
Take care of lenses radiation by tilting the gantry
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39. AEOI report INRARP6CP02
( Chapter 3 ) cont.
Mount danger sign and warning light
Pregnant women should informed technician
Occupational exposure should not exceed over permitted dose
limit
Fixed , portable and adjustable protective devices should be
available

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41. Thanks
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