Radiation Protection for Cardiologists

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Radiation Protection for Cardiologists
Part 3 Practical Protection for Patients Staff

• John Saunderson
• Radiation Protection Adviser
• PRH ext 6690

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Syllabus

• Physics hazards of ionising radiation to
  patients staff
• Statutory requirements for Medical Exposures
• Equipment
• Factors affecting patient staff dose
• Important aspects of cardioradiology
• Above covers IRMER Core of Knowledge.

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Part 1 Hazards of Ionising Radiation
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Deterministic Effects(threshold effects)

• Large number of cells killed physiological
  effect, e.g.
• Erythema, epilation, cateracts, radiation
  sickness
• No risk below threshold doses, e.g.
• Transient erythema 2 Gy
• Opacities 500 mGy
• Bigger dose above threshold, more severe the
  effect, e.g.
• 2 Gy transient erythema
• 20 Gy secondary ulseration.

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Stochastic Effects(chance effects)

• Where cells mutated in a such a way as to cause
• Cancer, hereditary disease
• Risk proportional to dose
• e.g abdomen X-ray risk risk of dying in a
  traffic accident in next year
• Minimise risk by keeping doses as low as
  reasonably achievable
• A.L.A.R.A.

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Absorbed Dose (D)

• Amount of energy absorbed per unit mass Dd?/dm
  units, 1 Gray (Gy) 1 J/kg
• Typical Values of D
• Radiotherapy dose 40 Gy to tumour (over several
  weeks)
• LD(50/30) 4 Gy to whole body (single dose)
• Typical 1 minute screening 20 mGy skin dose
• Chest PA 160 uGy skin dose
• Threshold for transient erythema 2 Gy .

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Effective Dose (E)

• Absorbed dose weighted for relative
  radio-sensitivity of different organs
• Units are Sieverts (Sv)
• Risk of inducing cancer or hereditary disease is
  proportional to Effective Dose
• 1 in 20,000 risk of fatal cancer from 1 mSv
• ( risk of dying in a road accident in next year)
• e.g.
• Pulmonary angiography 5.4 mSv
• Chest PA 20 uSv
• Annual background dose 2.5 mSv.

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Small risks so why worry?

• Average effective dose for angiography 6 mSv
• Risk of fatal cancer from 6 mSv only 1 in 3,300
• But, 321,174 angiography procedures in 2000
• So
• All exposures must be JUSTIFIED
• Doses to patients, and staff, must be As Low As
  Reasonably Achievable (ALARA principle) .

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Part 2 The Nature of Ionising Radiation
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80 kVp Diagnostic X-ray Beam
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At lower energies

• PHOTOELECTRIC ABSORPTION dominates
• Lots of contrast (density, size Z3)
• Less scatter, higher patient dose

At higher energies

• COMPTON SCATTERING dominates
• Less contrast (density, size)
• More scatter, lower patient dose.

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Still to do . . .

• Image formation, image intensifiers, flat plates,
  nuclear medicine imaging
• Practical radiation protection
• Staff
• Patients
• X-ray nuclear medicine
• Assessing doses
• Regulations and Guidelines
• Practical Session.

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Radiation Protection for Cardiologists
Part 3 Practical Protection for Patients Staff

• John Saunderson
• Radiation Protection Adviser
• PRH ext 6690

15
International Commission on Radiological
ProtectionPrinciples of Radiation Protection

• Justification
• Optimisation
• Limitation.

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The Justification of a practice

• No practice involving exposure to radiation
  should be adopted unless it produces sufficient
  benefit to the exposed individual or to society
  to offset the radiation detriment it caused.
• i.e. must be a net benefit.

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The Optimisation of Protection

• In relation to any particular source within a
  practice, the magnitude of individual doses, the
  number of people exposed, and the likelihood of
  incurring exposures where these are not certain
  to be received should be kept as low as
  reasonably achievable, economic and social
  factors being taken into account. This procedure
  should be constrained by restrictions on the dose
  to individuals (dose constraints), or the risks
  to individuals in the case of potential exposures
  (risk constraints), so as to limit the inequity
  likely to result from the inherent economic and
  social judgements.

ALARA as low as reasonably achievable
ALARP as low as reasonably practicable
.
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Individual Dose and Risk Limits

• The exposure of individuals resulting from the
  combination of all the relevant practices should
  be subject to dose limits, or to some control of
  risk in the case of potential exposure. These are
  aimed at ensuring that no individual is exposed
  to radiation risks that are judged to be
  unacceptable from these practices in any normal
  circumstances. Not all sources are susceptible of
  control by action at the source and it is
  necessary to specify the sources to be included
  as relevant before selecting a dose limit.
• Prevent deterministic effects
• Limit risk of stochastic effects to acceptable
  level.

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ICRPs Three Types of Exposure

• Occupational
• Medical
• Public

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Occupational Exposure

• 20 mSv a year effective dose
• 150 mSv a year to lens of eye
• 500 mSv a year to 1 cm2 of skin, hands and feet
• Fetus from declaration of pregnancy
• for external radiation, 2 mSv to surface of
  womans abdomen
• for radionuclides, 1/20 Annual Limit of Intake.

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Medical Exposure

• exposures incurred by individuals as part of
  their own medical diagnosis and treatment .
• and . . . individuals helping in the support and
  comfort of patients undergoing diagnosis and
  treatment (not occupationally) . . .
• No dose limits apply
• Consider dose constraints

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Public Exposure

• Limits apply to exposures from human activities
• 1 mSv a year effective dose
• in special circumstances, average over 5 years
• 15 mSv a year to lens of eye
• 50 mSv a year to 1 cm2 of skin
• (i.e. 1/10th of worker limit).

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Optimisation - ALARA
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Practical Patient Protection

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

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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. limbs
• Use lead shields were appropriate - e.g. gonad
  shields
• AP or PA?.

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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.

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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).

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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).

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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

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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

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Tube to Patient Distance
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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 .

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Time to erythema threshold dose(At 20 100
mGy/min, 70 cm FSD)

• 70 cm from focus 100 - 20 mins
• 50 cm from focus 50 - 10 mins
• 30 cm from focus 18 - 3½ mins

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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
• 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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Dose Settings

• Vary with manufacturer and model
• Beware - can vary between different sets of same
  manufacturer and model!
• Low dose
• more filtration, higher kV, less pulses/second
• High contrast
• less filtration, low kV, more pulses/second.

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Automatic brightness control
Brightness controlled by simultaneous adjustment
of kVp and mA
Brightness controlled mainly by adjustment of kVp
Tube heating ? kV x mA (99 energy goes to heat,
typically ¼ kW over few mm2) X-ray intensity ?
kV2 x mA Penetrating power? with kV? Contrast?
with kV?
The tube current is maximised at 3 mA
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Entrance Dose Rates for Standard Phantom
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Time to Reach 2 Gy for Standard Phantom
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Screening and Acquisitione.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)
• 1 min screening ? 7 spot images

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Dose Area Product

• Stochastic risks approx. proportional to DAP
• Skin dose is DAP / area irradiated
• 1 Gy.cm2 ? 3 mGy skin dose (2 Gy ?666 Gy.cm2)
• 1 Gy.cm2 ? 0.2 mSv effective dose .

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Dose Area Product

• Dose ? 1/distance2
• Area ? 1/distance2
• Therefore, dose x area indepenent of distance.

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DAP

• Stochastic risks approx. proportional to DAP
• Skin dose is DAP / area irradiated
• 1 Gy.cm2 ? 3 mGy skin dose (2 Gy ?666 Gy.cm2)
• 1 Gy.cm2 ? 0.2 mSv effective dose .

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20/11/96
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CT

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

MX800Quad, 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
.
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Pregnancy

• Diagnostic Medical Exposures Advice on Exposure
  to Ionising Radiation during Pregnancy
  (NRPB/CoR/RCR)
• out of print, but can be downloaded from
  www.nrpb.org/publications/misc_publications/advice
  _during_pregnancy.pdf
• Deterministic effects very unlikely
• Stochastic effects increase risk of childhood
  cancer.

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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

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

.
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• 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

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Infants and Children

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

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From www.info.gov.hk/dh/diseases/CD/photoweb/RSVac
utebronchiolitis-1.jpg
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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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Probability of fatal cancer(Atom bomb
survivors)
Risk per million per mGy

• i.e. children risk ? 3 x adult risk

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Also

• Use AECs
• Low attenuation table tops, etc. (e.g. c-fibre)
• Quality assurance
• DRLs

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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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Health screening

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

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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

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Radiation protection of staff

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

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Basic Principles

• Time
• Distance
• Shielding

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Distance

• Double distance 1/4 dose
• Triple distance 1/9th dose.

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Shielding
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Shielding
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Typical Transmission through Shielding (90 kV)

• 0.25 mm lead rubber apron ? 8.5
• 0.35 mm lead rubber apron ? 5
• 2 x 0.25 mm apron ? 2.5
• 2 x 0.35 mm apron ? 1.0
• Double brick wall ? 0.003
• Plasterboard stud wall ? 32
• Solid wooden 1 door ? 81
• Code 3 lead (1.3 mm) ? 0.1.

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Lead Apron Storage

• Always return to hanger
• Do not
• fold
• dump on floor and run trolleys over the top of
  them!!!
• X-ray will check annually
• But if visibly damaged, ask X-ray to check them.

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e.g. Coronary Angiogram

• Primary beam 100 mSv (4.9 min screening)
• Scattered dose 152 uSv _at_ 1 m (annual dose limit
  39 patients)
• Thru 0.25 mm Pb 13 uSv (461 patients)
• Thru 0.35 mm Pb x 2 1.5 uSv _at_ 1 m (4000
  patients)

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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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fin
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www.hullrad.org.uk
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Parameter Summary

• Parameter Quality/Penetration Intensity
• mA ? - ?
• kV ? ? ? (kV2)
• Filtration ? ? ?
• Distance - ? (1/r2)

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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).

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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).

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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).

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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.org.uk/publications/pubs-
  list2.htmprotection
• View at http//www.ipem.org.uk/publications/
  IRR99.html

82
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)

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Effective Dose (E)
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

• Absorbed dose weighted for relative
  radio-sensitivity of different organs
• Units are Sieverts (Sv)

• Risk of inducing cancer or hereditary disease is
  proportional to Effective Dose
• 1 in 20,000 risk of fatal cancer from 1 mSv
• ( risk of dying in a road accident in next year)

e.g. if gonads alone received 2 Gy to tissue, E
0.20 x 2 0.4 Sv.