General Radiation Safety

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Do not adjust your set
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Radiation Safety in Medical Practice

• John Saunderson
• Radiation Protection Adviser
• (TPRH ext. 6690, john.saunderson_at_hey.nhs.uk)

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Programme

• Introduction
• Radiation basics and hazards
• Organising radiation safety
• Any questions?

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• Ionising radiations
• x-rays
• gamma rays (?-rays)
• beta particles (?)
• electron beams

• Not ionising radiations
• lasers
• ultraviolet (UV)
• infrared (IR)
• ultrasound
• MRI

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Radiation basics and hazards

• Why is it dangerous?
• Radiation in hospitals

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Ionising radiation can cause chemical reactions
in the bodys cells which may

• do no harm
• kill the cell
• cause the cell to multiply out of control
  (cancer)
• cause the cell to misfunction in some other way.

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Where very large doses kill many cells

• radiation burns
• cateract
• radiation sickness.

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Threshold risksVery large doses onlyThe bigger
the dose, the more severe the effect
Staff doses never this big
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Cancer risksIt is assummed 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.
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Radiation in hospitals

• Radioactive substances
• nuclear medicine
• pathology
• radiotherapy
• X-ray sources
• Radiology
• Radiotherapy
• Pathology .

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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
• Public dose limit 1 mSv ? 17 patients
• CC constraint 5 mSv ? 83 patients
• Staff limit 6 mSv ? 100 patients.

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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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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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Organising radiation safety

• Controlled Areas
• Local Rules
• Radiation Protection Supervisor
• Radiation Protection Adviser
• Radiographer .

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IRMER

• Operators
• Training

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f i n
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Radiation Quantities and Units

• Dose
• e.g. skin dose
• Dose equivalent
• Effective dose

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Absorbed Dose (D)

• Amount of energy absorbed per kg
• Measured in Grays (Gy)
• 1 Gy 1000 mGy (milligray)
• 1 mGy 1000 ?Gy (microgray)
• gt 2 Gy to skin causes erythema (sun burn)

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Typical Values of D

• Radiotherapy dose 40 Gy to tumour (over several
  weeks)
• LD(50/30) 4 Gy to whole body (single dose)
• Annual background dose 2.5 mGy whole body
• Chest PA skin dose 160 uGy
• Mammo skin dose 9 mGy .

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Dose Equivalent (H)

• Measured in Sieverts (Sv)
• 1 Sv 1000 mSv (millisievert)
• 1 mSv 1000 ?Sv (microsievert)
• Dose equivalent absorbed dose x Q
• Q depends on type of radiation
• For X-rays, Q 1, so 1 Sv 1 Gy
• Alpha rays are ten times as dangerous as X-rays,
  so Q 10, so 10 Sv 1 Gy

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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

• Sum of equivalent doses to each tissue/organ x
  organ weighting factors E ?T wT.HT
• Units are Sieverts (Sv)
• Risk of cancer is proportional to effective dose

e.g. if breast alone received 2 mGy to tissue, E
0.05 x 2 0.1 mSv.
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Typical Values of E

• Barium enema 7 mSv
• CT abdomen 10 mSv
• Conventional abdomen 1 mSv
• Chest PA 20 uSv
• Annual dose limit for radiation workers 20 mSv
• Annual background dose 2.5 mSv .

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Old Units

• 100 rad 1 Gy 100cGy
• 100 rem 1 Sv
• 100 R ? 0.9 Gy

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ICRP System of Radiological Protection

• Justification
• no unnecessary exposures
• Optimisation
• keep doses as low as reasonably achievable
  (ALARA)
• Limitation
• dose limits for workers and staff
• diagnostic reference levels (DRL) for patients
• DRL for mammo. 2 mGy glandular dose .