1. First FRCR Examination in Clinical Radiology Diagnostic Radiology & Radionuclide Radiology (4b) Patient Dosimetry John Saunderson Radiation Protection Adviser
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2. RCR Syllabus
Methods
Diagnostic reference levels (including high dose techniques)
Magnitude and measurements
Radiation detectors and dose meters
Measurement of absorbed dose and dose rate in air .
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3. Radiation detectors and dose meters, measurement of absorbed dose and dose rate in air
Ionisation of air detectors
Ionisation chambers
Geiger-Muller tubes
Proportional counters
Others
Scintillation detectors
Solid state (e.g. diodes)
Stimulated luminescence (TLD / OSLD)
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4. Ionisation Chambers Conducting anode (+) and Cathode (-)
Typically between 100 and 400 V between
When irradiated, some air atoms are ionised
Positive ions attracted to cathode, negative to anode
A current flows and can be measured
Current  absorbed dose to air rate
1 coulomb of charge in dry air is released by joules of absorbed energy (no need to learn this!)
joules ÷ kg of air in chamber = grays absorbed dose to air

5. Ionisation Chambers
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6. Radiation detectors and dose meters, measurement of absorbed dose and dose rate in air
Ionisation of air detectors 
Ionisation chambers 
Geiger-Muller tubes
Proportional counters
Others
Scintillation detectors
Solid state (e.g. diodes)
Stimulated luminescence (TLD / OSLD)
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7. Geiger-Muller (GM Tubes)
Low pressure gas, high voltage (1000 V)
When irradiated, some gas atoms are ionised
High voltage accelerates electrons and ions towards electrodes, giving them more energy
These ionise more gas atoms causing a cascade
A pulse is produced, which is not dependant on the energy of the radiation in

8. GM Tube Energy response i.e. “grays per click”

9. GM Tube uses
Very sensitive to small amounts of radioactive material, so good contamination monitor
Thin window can detect alpha particles
If energy compensated, sensitive dose rate meter, for a particular range.
Can be very small and still sensitive, so good for pocket dosemeters.

10. Radiation detectors and dose meters, measurement of absorbed dose and dose rate in air
Ionisation of air detectors 
Ionisation chambers 
Geiger-Muller tubes 
Proportional counters
Others
Scintillation detectors
Solid state (e.g. diodes)
Stimulated luminescence (TLD / OSLD)
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11. Proportional counter
Half way between an ionisation chamber and a GM-tube
The size of the “click” is proportional to the energy of the photon

12. Radiation detectors and dose meters, measurement of absorbed dose and dose rate in air
Ionisation of air detectors 
Ionisation chambers 
Geiger-Muller tubes 
Proportional counters 
Others
Scintillation detectors
Solid state (e.g. diodes)
Stimulated luminescence (TLD / OSLD)
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13. Scintillation Detector
Good contamination monitor
Pulse height gives energy of X-ray photon
Can also be used for dose rate meter

14. Radiation detectors and dose meters, measurement of absorbed dose and dose rate in air
Ionisation of air detectors 
Ionisation chambers 
Geiger-Muller tubes 
Proportional counters 
Others
Scintillation detectors 
Solid state (e.g. diodes)
Stimulated luminescence (TLD / OSLD)
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15. Silicon diode detector
Act like ionisation chamber
Silicon much more dense than air, so can be a lot smaller than air ionisation chamber
Used for testing X-ray sets
Need to correct for energy to get tissue dose.

16. Radiation detectors and dose meters, measurement of absorbed dose and dose rate in air
Ionisation of air detectors 
Ionisation chambers 
Geiger-Muller tubes 
Proportional counters 
Others
Scintillation detectors 
Solid state (e.g. diodes) 
Stimulated luminescence (TLD / OSLD)
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17. Methods General radiology Fluoroscopy Computed Tomography
Nuclear Medicine .
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18. General radiology ESD Dose-Area Product (DAP) Effective dose .
Thermoluminescent dosemeter (TLD)
exposure factors
Dose-Area Product (DAP)
Effective dose .
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19. T.L.D. Crystals, e.g. lithium fluoride
Radiation causes electrons to be caught in “traps”
At lab. TLDs heated to 240oC
Electrons released, light emitted
Amount of light emitted proportional to dose .
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20. T.L.D.s +/- Small Tissue equivalent Read 1 Gy Easy for radiographer
No direct readout
Sensitive to heat, UV, dirt
Tricky to calibrate
Easy to loose
Special ones needed for low dose (e.g. chest) .
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21. Dose Area Product
Because dose falls with 1/d2 and area increases with d2, DAP is independent of distance.
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22. DAP +/- No fiddly TLD for radiographers! Only one number to record
Instant answer
Doesn’t take into account backscatter
Initial cost (several thousand £)
Units sometimes cause confusion (cGy.cm2, or Gy.cm2, Gy.m2) .
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23. Effective dose Complicated to calculate from ESD or DAP
Can use computer models which make assumptions on
field size
patient size
field position
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29. Fluoroscopy Dose-Area Product (DAP) Exposure factors Effective dose .
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30. DAP +/- for fluoroscopy
Instant answer, etc.
DAP moves with the tube
Gives good indication of relative risks of inducing cancer
Not directly linked to erythema risk.
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31. Exposure factors
Based on assumed FSDs, etc.
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32. Effective dose
Can be “fudged” using radiograph software.
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33. GAFCHROMIC film
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36. GAFCHROMIC film optical density is proportional to the absorbed dose
0.01 Gy to 50 Gy
Energy independent from 30 keV to 30 MeV
£20 per 14” x 17” sheet

37. Computed Tomography CT Dose Index (CTDI) Dose-length Product (DLP)
Effective dose
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38. CT Dose Index (CTDI) Applies to a single slice Can be used to compare
different slice widths
different physical filter
different scanners
etc.
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39. Dose-Length Product (DLP)
DLP = CTDI x n x T
Gives an idea of relative dose for a whole scan
Can be used to compare effect of pitch, etc.
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40. Effective dose
NRPB program similar to radiography one
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42. Here on 22/11/2018
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43. Diagnostic Reference Levels
Early 80’s survey
DRLs today
IRMER
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44. Mid-80’s survey Method Survey of twenty UK hospitals
13 most common views
For each patients (60-80kg) at
DAP or ESD by TLD measured.
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45. Mid-80’s survey Results E.g. Chest PA Median ESD = 0.18 mGy
Minimum ESD = 0.03 mGy
Maximum ESD = 1.43 mGy
Max / min = 48 !!.
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47. Mid-80’s survey Recommendation
Use 75th percentile as reference value
i.e. carry out local surveys and take action if average dose is greater than ¾ of national survey doses
e.g. for chest PA reference = 0.3mGy ESD
Send results to NRPB to review national reference doses every 5 years.
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48. DRLs today
A DRL is essentially a guide to the rather indistinct border between “good and normal practice” and “bad and abnormal practice”.
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49. IRMER 2017
r.2 “diagnostic reference levels” means dose levels in medical radiodiagnostic or interventional radiology practices, or, in the case of radio-pharmaceuticals, levels of activity, for typical examinations for groups of standard-sized individuals or standard phantoms for broadly defined types of equipment;
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50. IRMER & DRLs The employer must Operators must Regularly review DRLs
Make available to operators
Have regard to EU and UK national DRLs
Review whenever DRLs are consistently exceeded and take action where appropriate.
Medical Physics Expert must contribute
Collect dose estimates and provide to PHE on request
Operators must
adhere to employers DRLs (This does not apply to individual patients)

51. National DRLs
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55. Staff and Environmental Monitoring
Devices
TLD
OSLD
Electronic
Body
Extremity
Environment
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56. IRR2017 schedule 3 Dose Limits
Type of limit
Employee & trainees > 18
Trainee < 18
Others
Effective dose
20 mSv/y a
6 mSv/y
1 mSv/y f
Equivalent dose
Lens of the eye
20 mSv/y b
15 mSv/y
Skin c
500 mSv/y
150 mSv/y
50 mSv/y
Extremities d
a /y = in a calendar year, i.e. 1st January to 31st December
b With HSE permission up to 50 mSv/y if total in 5 years < 100 mSv (i.e. average <20mSv/y)
c averaged over 1 cm2
d “extremities” means a person’s hands, forearms, feet and ankles
e overaged over 5 years, as long as < 50 mSv in every year
f if resulting from medical exposure of another, total in 5 years must be < 5mSv
This regulation does not apply to persons undergoing medical exposures

57. Monitoring Effective Dose
External dose
TLD
OSLD
EPD - Electronic personal dosimeter
For classified workers, must come from an HSE Approved Dosimetry Service (ADS)
For fluoroscopy, if worn on trunk under lead apron HSE allow us to assume effective dose  badge dose
Internal radiation – e.g. measurement of tritium in urine

58. Luxel badges Wear underneath lead rubber apron
Assume dose to badge = effective dose
Can be worn for 2 weeks to 3 months (usually 1 month)
Must be returned promptly.
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59. Monitoring Skin Dose TLD Electronic Wear position depends on task
Finger stalls
Electronic
Wear position depends on task

61. Eye dose monitoring
TLD

62. f i n
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