1. 2014 version
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2. First FRCR Examination in Clinical Radiology General Radiation Protection (3h) John Saunderson Radiation Protection Adviser
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3. General Radiation Protection
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4. Medical and Dental Guidance Notes A good practice guide on all aspects of ionising radiation protection in the clinical environment
“an essential reference book for all those working with ionising radiation in medical or dental practice, including medical and dental staff, radiographers, scientific and technical staff, and their employers.”
240 pages, £20 (discount for bulk purchase!)
Buy from
21/04/2017

5. Medical and Dental Guidance Notes
General measures for radiation protection
Radiation protection of persons undergoing medical exposures
Diagnostic & interventional radiology
Dental radiology
Radiotherapy
Nuclear medicine and other uses of radioactive materials
(+ Appendices )
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6. Radiation protection of the patient
Justification - 
Optimisation - 
Limitation - X
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7. Ways to Optimising Patient Doses in Radiology
minimise exposure time
minimise radiation field size
maximise tube voltage (kV)
maximise beam filtration
maximise tube to patient distance (FSD)
minimise pulses per second
minimise acquisition images
minimise use of CT
have a good quality assurance programme

8. OPTIMISATION Field Size
Don’t irradiate more tissue than necessary
Larger fields =
larger doses to patient
larger doses to staff (from scattered radiation)
more scatter, resulting in more blurred images
Some examples of poorly collimated paediatric chest radiographs

9. OPTIMISATION Exposure Time
Don’t use X-rays at all if other non-radiation techniques can reasonably be used
Don’t irradiate for longer than necessary
If you are not looking at the monitor stop screening
Use the freeze frame facility whenever appropriate

10. OPTIMISATION X-Ray Tube Voltage (kV)
(more detail in lecture 4)
On some sets kV can be selected by the operator. On fluoroscopy sets it is normally selected automatically, but different user selectable settings will affect how the automatic kV works.
Higher kV radiation is more penetrating, so lower intensity beam into patient required to give same intensity out of patient to imager

11. From NIST Physical Reference Data (http://physics. nist
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12. Photoelectric Absorption
  m x Z3 / E3
 = linear attenuation coefficient for PE effect
m = mass density (kg/m3)
Z = atomic number
E = photon energy
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13. Compton Scattering   m x e / E
 = linear attenuation coefficient for PE effect
m = mass density (kg/m3)
e = electron density (e- per kg) [Z/A]
E = photon energy
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14. 21/04/2017
From NIST Physical Reference Data (

15. OPTIMISATION X-Ray Tube Voltage (kV) (continued)
Higher kV radiation is more penetrating, so lower intensity beam into patient required to give same intensity out of patient to imager
Therefore, higher kV = lower patient dose
e.g.
changing up from 90 to 110 kV may lead to a 26% reduction in skin dose
changing down from 90 to 70 kV may lead to a 62 % increase in skin dose
So at lower kV values the threshold for erythema can be reached in a shorter screening time
On some sets “low dose mode” forces the X-ray set to use higher kV settings, and “high contrast mode” forces it to use lower kV settings.

16. OPTIMISATION X-Ray Tube Voltage (kV) (continued)
But, because a higher kV beam is more penetrating then it will also less contrast between different materials
Therefore, higher kV = less contrast
Example – a 1 mm wire in the trunk, comparing 90kV to 110kV beam
Skin dose 26% lower for 110 kV
Effective dose 10% lower for 110 kV
Contrast 15% higher for 90 kV
You must have sufficient contrast to see what you need to in order to perform the clinical procedure, but a higher than necessary contrast can result in
a higher risk of patient skin reactions,
a higher risk of cancer induction in patients and staff, and
a higher risk of exceeding your eye or other dose limit which could prevent you working with X-rays until the following year.

17. OPTIMISATION Beam filtration
(more detail in lecture 4)
All X-ray sets must have a metal filter (typically around 2 mm of aluminium) to remove very low energy X-rays which would never penetrate the patient and reach the imager, but would significantly increase the dose to the patient.
Most modern fluoroscopy sets also have removable copper filters of a few tenths of a millimetre built into the X-ray tube housing. On some fluoroscopy sets the added copper filtration can be selected by the operator. On others it is normally selected automatically, but different user selectable settings will affect how much filtration is automatically driven into the beam.

18. OPTIMISATION Beam filtration (continued)
More filtration effectively means the average energy of the X-rays is higher, and so with more filtration the beam is more penetrating.
In exactly the same way as higher kV beams give lower patient skin dose but also lower contrast, more filtration will do exactly the same.
On some sets “low dose mode” forces the X-ray set to use extra copper filters, and “high contrast mode” forces it to use no copper filter.
Example – a 1 mm wire in the trunk in a 90kV beam,
comparing no copper filter with using a 0.1 mm copper filter
Skin dose 29% lower with 0.1 mm copper filter
Effective dose 4.3% lower with 0.1 mm copper filter
Contrast is 4.5% higher for no copper
Use the maximum filtration you can while still maintaining adequate image quality for the task you are undertaking.

19. 21/04/2017

20. 21/04/2017

21. Transmission through 10 cm tissue
80 keV  16 %
60 keV  13 %
50 keV  10 %
40 keV  7 %
30 keV  2 %
20 keV  0.04 %
15 keV  %
10 keV  %
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22. Minimum Filtration General tube  2.5 mm aluminium
Mammography  0.03 mm molybdenum or 0.5 mm Al
Dental ( 70kVp)  1.5 mm Al
Dental (> 70kVp)  2.5 mm Al
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23. 21/04/2017

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26. 21/04/2017

27. 21/04/2017

28. Tube to Patient Distance
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29. Tube to Patient Distance
Greater FSD = lower patient dose
e.g.  from 50 to 70 cm   49% skin dose
Greater FSD = less magnification
(so fewer distortions)
Tube to patient distance
never < 30cm,
preferably > 45cm
for chests > 60 cm .

30. Tube to Patient Distance
In fluoroscopy always have the patient
as close to the imager as possible
as far from X-ray tube as possible
Greater FSD# = lower patient dose
e.g.  from 50 to 70 cm FSD   49% skin dose
Greater FSD = less magnification (so fewer distortions)
(# FSD = focus to skin distance, where the focus is the source of the X-rays inside the X-ray tube)

31. One of the main causes of unnecessary radiation injury to patients is bad positioning, with the patient (or part of the patient such as their arm) too close to the X-ray tube
Approximate screening times to reach erythema threshold dose (At 20 – 100 mGy/min, 70 cm FSD)
70 cm from focus = mins
50 cm from focus = mins
30 cm from focus = mins

32. Fluoroscopy Only expose when looking at monitor
Keep patient close to image intensifier and far from tube (at least 30 cm from tube for mobile, 45 cm for static)
Use low dose setting, unless image unacceptable (i.e. high kV, high filtration)
Magnification increases dose rate to skin (although a smaller area irradiated)
Cone down where practicable
Special care if skin dose likely to exceed 1 Gy.
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33. 21/04/2017

34. 21/04/2017

35. 21/04/2017

36. Entrance Dose Rates for Standard Phantom
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37. Time to Reach 2 Gy for Standard Phantom
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38. Skin dose rate (mGy/min)
Field size
HRI CP1
Siremobil
Low dose
High dose
Cont.
Low mA
high mA
Pulsed
38 cm 17 19
25 cm 23 40
23cm 13 10 5
17 cm 28 49 12 6
Max.
125 70
Remedial level: 50 mGy/min for largest field (standard patient)
Suspension level: 100 mGy/min (standard patient)
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39. Frame rate / Pulses per second
Fewer pulses per second = less dose
e.g. 15 pps gives half the dose of 30 pps
Fewer pulses per second = potential blurring if there is patient/organ movement
Use the lowest frame rate you can while still maintaining adequate image quality for the task you are undertaking.

40. Fluoroscopy Dose Modes
“Low dose”
higher kV (lower mA)
more copper filtration
therefore, lower contrast
“High contrast”
lower kV (higher mA),
less copper filtration
therefore higher dose
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41. Screening and Acquisition
Screening uses a low dose rate, allowing movement to be observed.
Acquisition/spot images use a higher radiation dose for a short time to reduce noise in the image and take a high quality snapshot.
Only use acquisition when you really need the extra image quality, and then use sparingly.

42. Screening dose vs Acquisition dose e. g. HRI CP1, 20 cm field size, 18
Screening dose vs Acquisition dose e.g. HRI CP1, 20 cm field size, 18.5 cm Perspex phantom
Screening
77 kV, 2.2 mA
Skin dose rate  19 mGy/min
(Erythema threshold  105 min)
Digital acquisition
80 kV, 475 mA, 32 ms
Skin dose  2.5 mGy/image
(Erythema threshold  800 images)
So in this example, in terms of patient skin dose
1 spot image  8 seconds of screening

43. General Good Practice in Fluoroscopy
Only expose when looking at monitor (if you are not then the radiation dose to the patient and staff has no benefit)
Keep patient close to image intensifier and far from tube (at least 30 cm from tube for mobile, 45 cm for static)
Use low dose setting, unless image unacceptable
Magnification increases dose rate to skin (although a smaller area irradiated, effectively more dose is squeezed into a smaller area to get a bright enough image)
Cone down where practicable
Take special care if skin dose is likely to exceed 1 Gy, as erythema may be caused#.
                                     
Note, higher patient dose also means
higher dose to you and other staff in the X-ray room
(# some sets display “skin dose”, but this assumes an average size patient in a standard set up. So “1 Gy” displayed could be above the 2 Gy erythema threshold for a real patient.)

44. Here on 25/11/2014

45. Computed Tomography (CT)
(Covered in more detail in Craig Moore’s lectures)
High dose, so justification important
Lowest mA practicable
Minimum number of slices necessary
Angulation of gantry can substantially reduce eye dose.
21/04/2017 .

46. Individual procedure doses

47. Individual procedure doses (UK averages)
Conventional radiography CT
Head
0.068 mSv
C spine
0.03
Shoulder
0.011
Chest
0.014
T spine
0.38
L spine
0.6
Abdomen
0.43
Pelvis
0.28
Singel hip
0.087
Both hips
0.19
Femur
0.012
Knee
0.0002
Foot
IVU
2.1
CT head
1.4 mSv
CT chest
6.6
CT chest hi-res
1.2
CT abdomen
5.6
CT abdo-pelvis
6.7
CT chest-abdo-pelvis 10
Fluoroscopy
Ba swallow
1.5
Ba follow
1.3
Ba enema
2.2
Coronary angiography
3.9
Femoral angiography
2.3
HPA-CRCE

48. Comparing CT with general radiology

50. Computed Tomography (CT)
(Covered in more detail in Craig Moore’s lectures)
High dose, so justification important
Optimise protocols (e.g. lowest mA practicable)
Minimum number of slices necessary
Angulation of gantry can substantially reduce eye dose.
21/04/2017 .

51. Chest ‘only’

52. Dose quantities in CT Computed Tomography Dose Index (CTDI, in Gy)
Average dose inside the beam
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53. CTDIw = 1/3CTDI100(centre) + 2/3CTDI100(peripheral)
Weighted CTDI100
CTDIw = 1/3CTDI100(centre) + 2/3CTDI100(peripheral)
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54. Dose quantities in CT
Dose length Product (DLP, in Gy.mm)
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55. NRPB - W67 Doses from Computed Tomography (CT) Examinations in the UK - 2003 Review
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56. CT Dose Optimisation Don’t CT unless sufficient benefit
Don’t use very thin inefficient slices if unnecessary
Lowest mAs/slice for acceptable noise level
Understand Dose Modulation systems and use where appropriate
Largest pitch
Shortest scan length
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57. Pregnancy (link from http://www.hullrad.org.uk)
- can be downloaded from
(link from
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58. Radiation risks to the Embryo or Foetus
Deterministic effects
The radiation dose to the embryo or foetus that is likely to result from any diagnostic or interventional procedure in current use should present no risk of causing death, malformation, growth retardation or impairment of mental ability.
Stochastic effects
There is a increased risk of childhood cancer associated with irradiation in the womb

59. Pregnancy – Deterministic effects
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60. Radiation induced childhood cancer
The risk is around 1 in 10,000 for a 1 milligray dose to the foetus
The natural incidence of childhood cancer is around 1 in 500
The following slides give the range of foetal doses from common radiological procedures and the associated risks taken from the Health Protection Agency’s guidance. A few of particular interest in cardiology from these tables are
Examination
Typical foetal dose range
Risk of childhood cancer per examination
X-ray chest
<0.01 mGy
< 1 in 1,000,000
CT Pulmonary Angiogram
0.01 to 0.1 mGy
1 in 1,000,000 to 1 in 100,000
Nuclear medicine cardiac scans
1 to 10 mGy
1 in 10,000 to 1 in 1,000

61. Foetal doses and risk (1)

62. Foetal doses and risk (2)

63. Flow chart showing general principles
Is pregnancy possible? No
Proceed with examination
Yes
Flow chart showing general principles
see HPA guidance for more detailed (but straighforward) advice on application
( )
Is the patient definitely or probably pregnant?
Yes, possibly pregnant No
Would it be reasonable to delayed the procedure until after delivery, or confirmed not pregnant?
Yes
Delay
If pregnancy cannot be excluded, is this a low dose procedure?
(i.e. < 10 mGy foetal dose) No
Yes
No, high dose
Yes No
Proceed with examination, taking any practical steps to minimise foetal dose consistent with the clinical purpose.
Is the patient’s menstrual period overdue?
Will procedure be within first 10 days of menstrual cycle? No
Yes
Proceed with examination
Proceed with examination

64. e.g. CT pelvis CT pelvis & abdomen CT Pelvis, abdomen & chest
Myocardial Tc-99m scan
Whole body PET/CT scan .
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65. Inadvertent Foetal Exposure
If this happens, either due to staff or patient “error”
An investigation should be carried out in consultation with a Medical Physics Expert in accordance with Trust IRMER procedures
The MPE can provide a dose and risk estimate
The MPE can advice on whether the incident needs to be reported to the authorities under IRMER
Risk from a diagnostic X-ray is small enough never to be grounds for
invasive foetal diagnostic procedures
for termination

66. Infants and Children
Gonad shields should be used where relevant and practical
Restrict field to essential area
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67. 21/04/2017
From

68. Infants and Children
Gonad shields should be used where relevant and practical
Restrict field to essential area
Greater level of justification
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69. Infants and children
Higher risk of inducing cancer than adults .

70. Probability of fatal cancer (Atom bomb “survivors”)
From ICRP60 table B-12
0-19 y  24% per Sv (1 in 4,000 per mSv)
20-64 y  8% per Sv (1 in 12,000 per mSv)
0-90 y  10% per Sv (1 in 10,000 per mSv)
i.e. children risk  3 x adult risk
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71. Also Use AECs Properly calibrated CR
Low attenuation table tops, etc. (e.g. c-fibre)
Quality assurance
Good processing and viewing conditions
DRLs
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72. End of part 1
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73. First FRCR Examination in Clinical Radiology General Radiation Protection Part II John Saunderson Radiation Protection Adviser
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74. General Radiation Protection
Radiation protection of the patient including pregnancy, infants and children
Medical and biomedical research
Health screening
Radiation protection of staff and members of the public
Use of radiation protection devices.
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75. Medical & biomedical research
Must be LREC approved
If no benefit to individual - DOSE CONSTRAINTS
If benefit to patient - INDIVIDUAL TARGET LEVELS of DOSE
Risks must be communicated to volunteer
Avoid pregnant women or children unless specific to study.
Only one study a year for healthy volunteers.
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76. Health screening Medical Physics Expert must be consulted
Special attention to dose
Dose constraints
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77. e.g. is mammography screening of 40-49 year olds justified?
Currently 50-64’s screened
300+ lives saved per year (UK)
Between 0 and 2 in 1000 will have life extended if screened
For 50-64, 1 in 10 missed
For 40-49, 1 in 4 missed
1 in 10,000 risk of inducing cancer (40-49)
other “risks”
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78. Radiation protection of staff
Controlled areas
Time, distance, shielding
lead aprons
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79. Leakage
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80. 21/04/2017

81. 21/04/2017

82. 21/04/2017

83. Scatter Dose e.g. Lat. Lumbar spine
No lead apron: cm
With 0.35 mm apron: cm
(Primary skin dose: 16 mGy)
Public dose limit = 1 mSv  17 patients
C&C constraint = 5 mSv  83 patients
Staff limit = 6 mSv  100 patients.
Films rather than patients?
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84. Scatter dose from typical coronary angiography at 1 m
Higher scatter dose tube side, as scatter towards imager is partially absorbed by the patient

85. Doses Relative to Lum. Sp.
Chest: x 0.02
Skull: x 0.04
Thoracic spine, pelvis: x 0.5
Abdomen: x 0.8
IVU: x 1.5
Ba. Enema: x 4.1
CT abdomen: x 5.9.
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86. Radiology Staff Protection
Only essential staff in radiation area
Protective clothing if not behind screen
Close doors
Minimum beam size (min. scatter)
Never point primary beam at screen
Use mechanical devices to support patients (unless …)
Record where staff hold, rotate staff.
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87. Staff pregnancy
IRR99 – dose limit to foetus of employee is 1 mSv during declared term of pregnancy
For diagnostic radiology 2 mSv to abdomen  1 mSv to foetus
98% of imaging department staff in UK < 1 mSv/y effective dose (2005)
Diagnostic & interventional X-Ray staff monitored > 1mSv/y (n=10,336)
1 in 150 radiographers
1 in 40 diagnostic radiologists
1 in 16 interventional radiologists
1 in 61 other clinicians monitored
1 in 100 nurses monitored
1 in 200 others monitored
ancy_Work_Diagnostic_Imaging_2nd.pdfhttps:// ork_Diagnostic_Imaging_2nd.pdf
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88. Annual whole body occupational doses (UK 2005)
Nuclear medicine (non-PET) staff monitored > 1mSv/y (n=677)
1 in 6 pharmacists monitored
1 in 2-3 nuclear medicine technologists or radiographers
1 in 17 scientists
1 in 10 clinicians
1 in 3-4 nurses
1 in 73 others monitored
2007 survey of PET staff (n=58)
nearly 70% of staff > 1mSv/y
mean dose of 1.9 mSv
i.e. most pregnant PET staff will need to significantly alter work practice
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89. Radiation Protection of members of the public
Walls, doors, etc.
controlled areas
. . . comforters and carers.
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90. Comforters and Carers 21/04/2017
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure”
c.f. doses to patients in red book
Highly unlikely for a single exposure.
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91. Comforters and Carers
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure"
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure”
c.f. doses to patients in red book
Highly unlikely for a single exposure.
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92. Comforters and Carers
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure"
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure”
c.f. doses to patients in red book
Highly unlikely for a single exposure.
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93. Comforters and Carers
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure"
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure”
c.f. doses to patients in red book
Highly unlikely for a single exposure.
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94. Comforters and Carers
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure"
Dose constraint required.
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95. Comforters and Carers e.g. parent holding a child being X-rayed
not a nurse, care assistant, etc.
if < 1 mSv public dose limit, not “C&C”
5 mSv dose constraint
if pregnant 1 mSv dose constraint
must be aware of the risk.
"individuals who (other than as part of their profession) knowingly and willingly incur an exposure to ionising radiation in the support or comfort of another person who is undergoing, or has undergone a medical exposure”
c.f. doses to patients in red book
Highly unlikely for a single exposure.
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96. Radiation protection devices
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97. Guidance Notes Gloves, aprons eyewear
Protect from scatter or transmitted radiation, NOT primary
Must be marked with lead (Pb) equivalence & CE
Body aprons
Not less than 0.25mm Pb for up to 100kV
Not less than 0.35mm Pb for over 100kV
HSE assumes dose under apron is effective dose
Gloves no less than 150kV
Do not use half body aprons
Hang carefully, never fold,
Check at least annually by fluoroscopy.
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98. Transmission through Lead Aprons
0.25 mm Pb
60 kV, T = 1.5 %
90 kV, T = 9.5 %
120 kV, T = 17.5%
0.35 mm Pb
60 kV, T = 0.5 %
90 kV, T = 4.9 %
120 kV, T = 11.3 %
2 x 0.35 mm
90 kV, T  1.1 %

99. Light weight aprons
Use materials with different Z and density than lead (e.g. tungsten, barium)
Note kV of Pb equivalence!
Sometimes just smaller & shorter!
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100. Thyroid shields Usually 0.5mm Pb Transmission = 2.5% @ 90kV
Tissue or organ wT (2007)
Gonads 0.08
Red bone marrow 0.12
Colon
Lung
Stomach 0.12
Bladder 0.04
Breast 0.12
Liver
Oesophagus 0.04
Thyroid 0.04
Skin
Bone surfaces 0.01
Brain
Salivary glands 0.01
Remainder 0.12
Usually 0.5mm Pb
Transmission = 90kV
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101. Eye Protection (1)
Threshold for detectable opacities = 500 mGy to lens
ICRP dose limit for lens of eye = 150mSv a year 20 mSv/y (averaged over 5 years)
Glasses 0.75mm Pb
Direct transmission 90kV, but
But in reality 13%-33% because of scatter around edges etc.
Mask 0.1mm Pb
Direct transmission 90kV
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102. Eye Protection (2) Lead acrylic or lead glass screens
Overhead screens typically 0.5mm Pb
Direct transmission = 90kV)
But in reality 13%-66% because of scatter around edges etc.
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103. Hand protection Threshold for transient erythema = 2,000 mGy
ICRP dose limit for hands, feet, skin = 500 mSv a year
Gloves
0.5mm Pb 90kV)
1.4 kg each
Thin gloves
0.3mm at finger tip
90kV

104. Gonad Protection (patient)
Solid 2mm Pb
90kV
Flexible 0.5mm Pb
90 kV
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105. Others
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106. Transmission through Other Materials
Code 3 Pb (1.3 mm)
120 kV, T = 0.7 %
9” of red brick
120 kV, T = 0.04 %
2 x 10 mm plasterboard
120 kV, T  52. %
1” wood
120 kV, T = 86 %
5 mm plate glass
120 kV, T = 63. %

107. Fin
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108. Here on 2/12/2014
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