Radiation Kilo Curie

1
2006 version
2
First FRCR Examination in Clinical Radiology
General Radiation Protection(3h)John
SaundersonRadiation Protection Adviser
3
General Radiation Protection

• 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.

4
Medical and Dental Guidance Notes A good
practice guide on all aspects of
ionisingradiation 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 http//www.ipem.ac.uk

5
Medical and Dental Guidance Notes

• 1. General measures for radiation protection
• 2. Radiation protection of persons undergoing
  medical exposures
• 3 - 4. Diagnostic interventional radiology
• 5 - 6. Dental radiology
• 7- 9. Radiotherapy
• 10-18. Nuclear medicine and other uses of
  radioactive materials
• ( Appendices 1 - 21)

6
Radiation protection of the patient

• Justification - ?
• Optimisation - ?
• Limitation - X

7
Practical Patient Protection

• Field
• Tube voltage
• Beam filtration
• Tube to patient distance
• Fluoroscopy
• CT
• QA

8
Field

• Cover only area needed

• Small fields give lower dose (and less scatter,
  therefore better image)
• Avoid more radiosensitive areas - e.g. gonads,
  female breast
• Position carefully - e.g. limb examinations
• Use lead shields were appropriate - e.g. gonad
  shields
• AP or PA?.

9
Lead rubber

• 0.35 mm
• 60 kVp ? 0.5 transmission
• 120 kVp ? 10 transmission
• 0.25 mm
• 60 kVp ? 1.5 transmission
• 120 kVp ? 16 transmission.

10
Tube Voltage (kV)

• Higher kV lower patient dose
• e.g. changing from 100 to 110 kV leads to 12
  reduction in skin dose
• Higher kV less contrast
• e.g. changing from 100 to 110 kV reduces
  spine/soft tissue contrast from 1.48 to 1.34 (9
  drop).

11
From NIST Physical Reference Data
(http//physics.nist.gov/PhysRefData/XrayMassCoef/
cover.html)
12
Photoelectric Absorption

• ? ? ?m x Z3 / E3
• ? linear attenuation coefficient for PE effect
• ?m mass density (kg/m3)
• Z atomic number
• E photon energy

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

14
From NIST Physical Reference Data
(http//physics.nist.gov/PhysRefData/XrayMassCoef/
cover.html)
15
Tube Voltage (kV)

• Higher kV lower patient dose
• e.g. changing from 100 to 110 kV leads to 12
  reduction in skin dose
• Higher kV less contrast
• e.g. changing from 100 to 110 kV reduces
  spine/soft tissue contrast from 1.48 to 1.34 (9
  drop).

16
Filtration

• More filtration lower patient dose
• e.g. ? 0.1 mm Cu ? ? 33 skin dose
• More filtration less contrast
• e.g. ? 0.1 mm Cu ? ? spine/soft tissue contrast
  at 80 kV from 2.76 to 2.46 (11 drop).

17
(No Transcript)
18
(No Transcript)
19
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 ? 0.000008
• 10 keV ? 10-21

20
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 (gt 70kVp) ? 2.5 mm Al

21
(No Transcript)
22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
Tube Voltage (kV)

• Higher kV lower patient dose
• e.g. changing from 100 to 110 kV leads to 12
  reduction in skin dose
• Higher kV less contrast
• e.g. changing from 100 to 110 kV reduces
  spine/soft tissue contrast from 1.48 to 1.34 (9
  drop).

27
Tube to Patient Distance
28
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 lt 30cm,
• preferably gt 45cm
• for chests gt 60 cm .

29
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.

30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
Entrance Dose Rates for Standard Phantom
34
Time to Reach 2 Gy for Standard Phantom
35
Skin dose rate (mGy/min)
Remedial level 50 mGy/min for largest field
(standard patient) Suspension level 100 mGy/min
(standard patient)
36
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

37
CT

• High dose, so justification important
• Lowest mA practicable
• Minimum number of slices necessary
• Angulation of gantry can substantially reduce eye
  dose
• CT 10 x 1mm slices may give higher dose than 1 x
  10mm slice .

MX8000Quad, HRI CTDI/mAs vs Slice Thickness 2 x
10 mm ? 191 uGy/mAs 2 x 8 mm ? 197 uGy/mAs 4 x
5 mm ? 190 uGy/mAs 4 x 2.5 mm ? 208 uGy/mAs 4 x
1 mm ? 253 uGy/mAs 2 x 0.5 mm ? 445 uGy/mAs
.
38
Dose quantities in CT

• Computed Tomography Dose Index (CTDI, in Gy)
• Average dose inside the beam

39
Weighted CTDI100

• CTDIw 1/3CTDI100(centre) 2/3CTDI100(peripheral
  )

40
Dose quantities in CT

• Dose length Product (DLP, in Gy.mm)

41

• Got to here on 3rd Oct 06

42
Pregnancy

• Diagnostic Medical Exposures Advice on Exposure
  to Ionising Radiation during Pregnancy
  (NRPB/CoR/RCR)
• - out of print, but can be downloaded from
  www.hpa.org.uk/radiation/publications/misc_publica
  tions/advice_during_pregnancy.htm

43
Pregnancy - Radiation Risks
44
(No Transcript)
45
Fetal Doses from Medical Exposure (mGy)
46
Fetal Doses from Medical Exposure (mGy)
47
Examples of Risk of Childhood Cancer

• Natural risk 1 in 1,300
• Abdomen mean 1.4 mGy ? 1 in 24,000
• max. 4.2 mGy ? 1 in 8,000
• CT Abdomen mean 8 mGy ? 1 in 4,000
• max. 49 mGy ? 1 in 700
• Pelvis mean 1.1 mGy ? 1 in 30,000
• max. 4.0 mGy ? 1 in 8,000
• CT Pelvis mean 8 mGy ? 1 in 4,000
• max. 79 mGy ? 1 in 400

48

• e.g.
• abdominal CT (max. fetal dose 49mGy)
• pelvic CT (79mGy)
• 131I thyroid metastases (22mGy)
• 75Seleno-cholesterol (14mGy)
• 67Ga tumours and abscesses (12mGy).

.
49
.

• If fetus inadvertently exposed contact RPA for
  risk estimate
• Risk from a diagnostic X-ray is small enough
  never to be grounds for
• invasive fetal diagnostic procedures
• for termination

50
Infants and Children

• Gonad shields should be used where relevant and
  practical
• Restrict field to essential area

51
From www.info.gov.hk/dh/diseases/CD/photoweb/RSVac
utebronchiolitis-1.jpg
52
Infants and Children

• Gonad shields should be used where relevant and
  practical
• Restrict field to essential area
• Greater level of justification

53
Infants and children

• Higher risk of inducing cancer than adults .

54
Probability of fatal cancer(Atom bomb
survivors)

• From ICRP60 table B-12
• 0-19 y ? 24 x 10-2 per Sv (1 in 4,000 per mSv)
• 20-64 y ? 8 x 10-2 per Sv (1 in 12,000 per mSv)
• 0-90 y ? 10 x 10-2 per Sv (1 in 10,000 per mSv)
• i.e. children risk ? 3 x adult risk

55
Risk Calculations

• Annual UK from diagnostic X-ray 19000 manSv
• 1000 manSv
• 99 probability of ? 34 fatal cancers
• 50 probability of ? 50 fatal cancers
• 2000 manSv
• 99 probability of ? 77 fatal cancers
• 50 probability of ? 100 fatal cancers

56
Also

• Use AECs
• Fast films (400)
• Low attenuation table tops, etc. (e.g. c-fibre)
• Quality assurance
• Good processing and viewing conditions
• DRLs

57
End of part 1
58
First FRCR Examination in Clinical Radiology
General Radiation ProtectionPart IIJohn
SaundersonRadiation Protection Adviser
59
General Radiation Protection

• 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.

60
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.

61
Health screening

• Medical Physics Expert must be consulted
• Special attention to dose
• Dose constraints

62
e.g. is mammography screening of 40-49 year olds
justified?

• Currently 50-64s screened
• 300 lives saved per year (UK)
• Between 0 and 2 in 1000 will have life extended
  if 40-49 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

63
Radiation protection of staff

• Controlled areas
• Time, distance, shielding
• lead aprons

64
Leakage
65
(No Transcript)
66
(No Transcript)
67
(No Transcript)
68
Scatter Dosee.g. Lat. Lumbar spine

• No lead apron 0.6 mGy _at_ 30 cm
• With 0.35 mm apron 0.06 mGy _at_ 30 cm
• (Primary skin dose 16 mGy)
• Public dose limit 1 mSv ? 17 patients
• CC constraint 5 mSv ? 83 patients
• Staff limit 6 mSv ? 100 patients.

69
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.

70

• Here on 10 Oct 06

71
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.

72
Radiation Protection of members of the public

• Walls, doors, etc.
• controlled areas
• . . . comforters and carers.

73
Comforters and Carers
74
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"
75
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"
76
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"
77
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.
78
(No Transcript)
79
Comforters and Carers

• e.g. parent holding a child being X-rayed
• not a nurse, care assistant, etc.
• if lt 1 mSv public dose limit, not CC
• 5 mSv dose constraint
• if pregnant 1 mSv dose constraint
• must be aware of the risk.

80
Radiation protection devices
81
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 0.25mm _at_ 150kV
• Do not use half body aprons
• Hang carefully, never fold,
• Check at least annually by fluoroscopy.

82
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

83
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!

84
Thyroid shields
Tissue or organ wT Gonads 0.20 Red bone
marrow 0.12 Colon 0.12 Lung 0.12 Stomach 0
.12 Bladder 0.05 Breast 0.05 Liver 0.05 Oe
sphagus 0.05 Thyroid 0.05 Skin 0.01 Bone
surfaces 0.01 Remainder 0.05

• Usually 0.5mm Pb
• Transmission 2.5 _at_ 90kV

85
Eye Protection (1)

• Threshold for detectable opacities 500 2,000
  mGy to lens
• ICRP dose limit for lens of eye 150mSv a year

• Glasses 0.75mm Pb (0.9 _at_ 90kV)

• Mask 0.1mm Pb (25 _at_ 90kV)

86
Eye Protection (2)

• Lead acrylic or lead glass screens
• Overhead screens typically 0.5mm Pb (2.5 _at_ 90kV)

87
Hand protection

• Threshold for transient erythema 2,000 mGy
• ICRP dose limit for hands, feet, skin 500 mSv a
  year

• Gloves
• 0.5mm Pb (1.2 _at_ 90kV)
• 1.4 kg each

• Thin gloves
• 0.3mm at finger tip
• 39 _at_ 90kV

88
Gonad Protection (patient)

• Solid 2mm Pb
• 0.01 _at_ 90kV

• Flexible 0.5mm Pb
• 2.5 _at_ 90 kV

89
Others

90
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.

91
fin