4/4/03 1

Do not adjust your set

4/4/03 2

Radiation Safety in the Mortuary (II)

John Saunderson

Radiation Protection Adviser

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Programme

Review of radiation risks

Potential source of radiation in the mortuary

Safety precautions and actions

Any questions?

4

Deterministic Effects(“threshold effects”)

• Large number of cells killed – physiological effect, e.g.– Skin burn– Cateracts– “Radiation sickness”

• No risk below threshold doses

• Bigger dose above threshold, more severe the effect

• Very unlikely in mortuary.

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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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Radiation in Hospitals

• Radioactive substances– Nuclear medicine– Pathology– Radiotherapy– Contaminated casualties

• X-ray sources– Radiology– Radiotherapy– Pathology

Radiation in Mortuary

• Radioactive substances– Nuclear medicine patients– Some radiotherapy patients– Contaminated casualties– Plutonium pacemakers

• X-ray sources– Mobile X-ray (?)

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External & Internal Hazards

• X-rays– External

• Radioactive substance– Internal – External

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X-ray tube

Primary beam

Scattered radiation

Patient

Leakage

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X-rays - some numbers• For an abdominal X-ray

– Patient dose = 1 mSv (milli-Sievert)– Scatter dose < 0.04 mSv at 1 metre

• Legal dose limit – for radiation worker = 20 mSv/y– Public = 1 mSv/y

• Natural UK background dose = 2.3 mSv/y.

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All doses should be kept

• As

• Low

• As

• Reasonably

• Achievable

The ALARA Principle .

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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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“Radioactive Patients”Patients may be radioactive if• they’ve been injected with

or swallowed radioactive pharmaceuticals

• they have solid radioactive sources surgically implanted

• they have been involved in an accident with radioactive materials .

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Beginning After 1 half life

After 2 half lives

After 3 half lives

After 4 half lives

After 5 half lives

Radioactive Decay - half life

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Radiation measurements• Becquerels – Bq – measures activity

– Banana – 13 Bq– Natural radioactivity in a human – 3 kBq– Myocardial Perfusion Scan – 80 MBq (2 mCi)

– Thyroid cancer - 8 GBq– Radiotherapy Co-60 source – 150 TBq (4 kCi)

• Sieverts – Sv – dose– Fatal dose – 4 Sv– Background UK dose = 2 mSv a year– Chest X-ray – 20 uSv

Nuclear Medicine Scan

• Patient injected with or swallows a radioactive pharmaceutical

• Gamma camera traces where that radiopharmaceutical is concentrated .

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Nuclear Medicine scan - some numbers

• For a bone scan (technetium-99m, half life = 6 hours)– Patient dose = 3 mSv – External dose < 0.01 mSv/h at 1 metre

– Activity injected = 600 MBq– ALI for radiation workers = 1000 MBq– To reach public dose limit = 50 MBq

• Legal dose limit – for radiation worker = 20 mSv/y– Public = 1 mSv/y

• Natural UK background dose = 2.3 mSv/y.

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Body of diagnostic patient

• Dose to patient similar to annual background radiation• External dose rate to others – insignificant• Half life

– Technetium-99m, 6 hours– Thallium-201, 73 days

• Contamination hazard?– “no extra precautions to those employed when caring out

post-protems/embalming”

• No restrictions on disposal of body• If in doubt, call Nuclear Medicine Department.

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Thyroid treatments with radio-iodine

•Hyperthyroidism / thyrotoxicosis

•overactive thyroid - 400 MBq

•Thyroid cancer

•must destroy all tumour - 3000 MBq

•c.f. thyroid scan - 0.2 MBq.

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Other unsealed source therapies

• Phosphorus-32 for polycythemia (too many red blood cells)

• Yttrium-90 colloid for arthritic conditions

• Strontium-90 for bone metastases.

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Body of unsealed source therapy patient

• Patient will have letter saying how many days restrictions apply. If they still apply– Seek advice of Medical Physics Expert (MPE) from Nuclear Medicine

Department

• External dose rate to others – low• Half life, iodine-131, 8 days • Contamination hazard?

– assume yes– Avoid spread of contamination

• Consult MPE on disposal of body– Thyrotoxicosis – OK– Thyroid cancer – OK after 23 day max..

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Brachytherapy (radioactive implants)

• Intracavity afterloading

• Iridium wire afterloading

• Iridium pins

• Iodine-125 seeds .

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LDR-Selectron

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HDR-microSelectron

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Iridium Implant

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Iodine-125 seeds in Prostate

4.5 x 0.8 mm “seeds”

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Body with iodine-125 seeds

• Very short range radiation (HVT = 2 cm tissue)• External dose rate to others – low

– Patients advised to avoid close contact (<10 cm) with children and pregnant women for 2 months

• Half life = 60 day• Avoid cremation before one year (or consider

removing sources)

• Post-mortem? – risk assessment – call the Radiotherapy Department.

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Nuclear Powered Pacemaker

• Contain 114 GBq of plutonium-238 • Not used for past 20 years• Never used in Hull & E. Yorks.• No longer fitted (NiCd batteries replaced nuclear batteries)• Patients wear a labelled bracelet• Should always be removed before buriel/cremation (although

designed to withstand 850oC)

• Annual dose limit exceeded if held for over 1600 hours.

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Casualties Contaminated by Low Level Radioactive Substances

• Life saving treatment will override all other action

• Seek expert advice from radiation physicist a.s.a.p.

• Avoid spread of contamination

• Collect everything that comes into contact with radioactive substances (e.g. clothes, swabs, fluids, etc.).

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f i n

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Threshold risksVery large doses only

The bigger the dose, the more severe the effect

5000

3500

3000

2500

2000

500 500

150

0

1000

2000

3000

4000

5000

6000

Cataracts

Perm

. male

sterility

Temp.

epilation

Fem

alesterility

Transient

erythema

Detectable

opacities(lens)

Supression of

bone marrow

Temp. m

alesterility

mill

i-si

ever

ts

Staff doses never this big

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Cancer risksIt is assumed that any dose of radiation could potentially

cause cancer.The bigger the dose, the more likely the effect will occur, (but it will probably never occur).

i.e. a bit like crossing the road - the more times you cross the more likely you are to be run over, but probably never will.

Risk of Fatal Cancer in one year for adult workers

0500

10001500200025003000

ClassifiedWorker

limit

Otherstaff limit

Publiclimit

1000 uSv Naturalcancerrisk (allages)

Cha

nce

in a

mill

ion

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Tc-99m 0.017 uGy/h/MBq@1m

Bone scan 600 MBq

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Unsealed source therapy - some numbers

• For thyrotoxicosis dose (iodine-131, half life = 8 days)– External dose < 23 mSv/h at 1 metre

– Activity swallowed = 400 MBq– ALI for radiation workers = 0.8 MBq

• Max. activity for burial or cremation without precautions = 400 MBq.