Introduction to radiation protection Review of CT Radiation protection in CT Equipment & layout of room Principles & guidelines

1. In the Name ofIn the Name of
GodGod

2. Radiation ProtectionRadiation Protection
in CTin CT
Seyedeh Shokoofeh Mousavi Gazafroudi
Seyedeh Shabnam Mousavi Gazafroudi
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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
Riskis 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 higherthan doses
encountered in CT demonstrated
increased cancers.
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6. 12/17/17 Isfahan University of Medical
Sciences
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8. 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 reasonablyas low as reasonably
achievableachievable (ALARA) below the limits established by
regulatory agencies.
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9. Factors in radiation protection
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10. Principles of radiological
protection
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11. Review of CT

12. 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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13. Effective dose estimation
CTDI is equivalent to dose distribution integrated over the
z (longitudinal) patient axis divided by the slice thickness
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14. Radiation Protection in
CT

15. 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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16. 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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17. Patient dose in CT
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These
parameters
affect on
patient
absorbed dose :

18. 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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19. Equipment & layout of
room

20. Stationary CT rooms
 Computed
tomography rooms
typically have high
workloads and high
kilo voltage
technique settings.
gantry
coach
operator
Isodosecurves12/17/17 Isfahan University of Medical Sciences 20

21. 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
factors.12/17/17 Isfahan University of Medical Sciences 21

22. Equipment & facilities
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23. 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
radiation protection programs.
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24. 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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25. Principles &
Guidelines

26. 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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27. ICRP recommendations
to reduce patient dose
Actions for 3 groups are defined:
 Operator
 Manufacture
 Physicians
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28. 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
Record of dose, exposure factors12/17/17 Isfahan University of Medical Sciences 28

29. 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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30. 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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31. 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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32. 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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33. 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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34. 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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35. 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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36. Thanks
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