Radiation Kilo Curie

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Do not adjust your set
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Radiation Protection Refresher for Dental Staff

• 4 February 2004
• John Saunderson,
• Radiation Protection Adviser

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Wilhelm Roentgen

• Discovered X-rays on 8th November 1895

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Colles fracture 1896
Frau Roentgens hand, 1895
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First Dental Radiograph

• Otto Walkhoff (Dentist - Braunschweig, Germany)
• Jan.1896 (lt2 weeks after Roentgen announced
  discovery of X-rays)
• 25 minute exposure.

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1 Feb 1896

• Walter Konig (physicist, Germany)
• 9 min. exposure

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Dr Rome Wagner and assistant
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First radiograph of the human brain 1896
In reality a pan of cat intestines photographed
by H.A. Falk (1896)
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First Reports of Injury

• Late 1896
• Elihu Thomson - burn from deliberate exposure of
  finger

Edisons assistant - hair fell out scalp became
inflamed ulcerated
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Edmund Kells

• April 1896 built own X-ray machine, packed films
  in rubber and took X-ray of his dental assistant
• 10 years on, cancer of right hand
• 42 operations in next 20 years lost hand, arm
  and shoulder.

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Testing X-ray Sets the early days
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William Rollins

• Rollins W. X-light kills. Boston Med Surg J
  1901144173.
• Codman EA. No practical danger from the x-ray.
  Boston Med Surg J 1901144197

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• Dental office - 1913
• Lead glass shield used
• (Although high voltage wires not!).

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How does radiation cause harm?

• LD(50/30) 4 Gy
• 280 J to 70 kg man
• 1 milli-Celsius rise in body temp.
• drinking 6 ml of warm tea

• i.e. not caused by heating, but ionisation
• Damages DNA.

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Where very large doses kill many cells

• radiation burns
• cateract
• radiation sickness.

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Dose measurements

• Skin dose, cone end dose Grays
• 1 Gy 1,000 mGy 1,000,000 uGy
• sometimes Sieverts used. For dental 1 Sv 1Gy
• e.g. cone end dose typically 2 mGy
• Effective dose Sieverts
• 1 Sv 1,000 mSv 1,000,000 uSv
• Dose averaged over whole body
• e.g. UK background dose about 2.5 mGy

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Deterministic (threshold) risksVery large doses
onlyThe bigger the dose, the more severe the
effect
Staff doses never this big
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Stochastic Effects

• Caused by cell mutation leading to cancer or
  hereditary disease
• Current theory says, no threshold
• The bigger the dose, the more likely effect
• So how big is the risk?.

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Cancer deaths between 1950 and 1990 among Life
Span Study survivors with significant exposure
(i.e. gt 5 mSv or within 2.5 km of the
hypercentre)
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Fraction of cancers induced by radiation
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Fraction of cancers induced by radiation
? Risk of inducing fatal cancer 1 in 20,000 per
mSv
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Data Sources for Risk Estimates

• North American patients - breast, thyroid, skin
• German patients with Ra-224 - bone
• Euro. Patients with Thorotrast - liver
• Oxford study - in utero induced cancer
• Atomic bomb survivors - leukaemia, lung, colon,
  stomach, remainder .

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ICRP risk factors
5.0 x 10-5 per mSv ? 1 in 20,000 chance .
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Pregnancy - Radiation Risks
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For diagnostic procedures

• Doses unlikely to be high enough to cause fetal
  death or malformation
• Increased risk of childhood cancer
• Risks must be assessed for each individual case.

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Doses in Dentistry

• Threshold for skin burn 2 Gy 2,000 mGy
• 1 mSv gives 1 in 20,000 risk of fatal cancer
• Skin dose from mandibular molar lt 0.01 Gy (10
  mGy)
• Effective dose from
• intraoral 0.005 mSv
• panoramic 0.010 mSv
• Dose to staff 1.5 m from patient 0.0003 mSv

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Risks in Dentistry

• No risk of deterministic effects
• Risks of inducing fatal cancer
• Intraoral 1 in 4 million per film
• Panoramic 1 in 2 million per film
• Staff at 1.5 m 1 in 67 million per film
• SO WHY WORRY ABOUT SUCH SMALL RISKS??

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700 CANCER CASES CAUSED BY X-RAYS
30 January 2004

• X-RAYS used in everyday detection of diseases and
  broken bones are responsible for about 700 cases
  of cancer a year, according to the most detailed
  study to date.
•  
• The research showed that 0.6 per cent of the
  124,000 patients found to have cancer each year
  can attribute the disease to X-ray exposure.
  Diagnostic X-rays, which are used in conventional
  radiography and imaging techniques such as CT
  scans, are the largest man-made source of
  radiation exposure to the general population.
• Although such X-rays provide great benefits, it
  is generally accepted that their use is
  associated with very small increases in cancer
  risk.
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Because large numbers exposed

• UK 2000
• 13 million dental X-rays
• 31 of diagnostic X-rays
• (0.4 of dose)
• 1 in 4 million risk per X-ray
• Therefore, high probability that radiation from
  angiography will kill some patients (approx. 3 a
  year)
• So
• All exposures must be JUSTIFIED
• Doses to patients, and staff, must be As Low As
  Reasonably Achievable (ALARA principle) .

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International Commission on Radiological
Protection System of Radiological Protection

• Justification
• Optimisation
• Limitation.

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Justification

• For any radiation exposure the benefits must
  outweigh the risks
• i.e. Never X-ray a patient unless it is necessary
• No unnecessary staff in room while X-raying.

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Basic Principles of Optimisation

• Time
• Distance
• Shielding

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Leakage
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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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Organising radiation safety

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

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Optimising Patient Doses

• Fast films
• Good processing
• Long cones
• High kVs
• QA and maintenance
• Training

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Limitation

• Legal dose limits
• Dose constraints
• Investigation levels
• Dose Reference Levels

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IRR99 Dose limits for Dental Work

• Staff operating X-ray units - 6 mSv a year
  effective dose
• 150 mSv to skin, etc., 45 mSv to lens of eye
• Member of the public - 1 mSv a year effective
  dose
• Fetus of an employee - 1 mSv during declared term
• Patient receiving medical exposure - no limit
• Comforter carer - no limit.

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Staff doses vs dose limits

• Dose to staff 1.5 m from patient 0.0003 mSv
• So, if
• 50 films taken a week
• for 48 weeks a year
• Staff dose 50 x 48 x 0.0003 0.72 mSv.

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Dose Constraints

• Used in designing radiation protection
  precautions
• Dental operators 1 mSv
• Public, other staff 0.3 mSv
• Used for comforters and carers
• 5 mSv
• If pregnant, 1 mSv
• Used for medical research.

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Dose Investigation Level

• Set locally
• 1 mSv recommended
• If exceeded have internal investigation.

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Diagnostic Reference Levels

• Average dose for a sample of patients should be
  below DRL
• If not, investigate
• Dental DRLs
• Mandibular molar 2 mGy cone end dose
• Panoramic 65 mGy.mm
• Checked annually on radiation protection survey.

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Doses Much Greater Than Intended

• For dental, x 20
• If machine fault report to HSE
• If other reason report DoH.

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Typical Intra-Oral Staff Doses

• Cone end dose 2 mGy per film
• Operator dose limit lt 3 films per year
• Primary at 1 m 0.08 mGy per film
• Public dose constraint lt 4 film per year
• Operator dose constraint lt 13 film per year
• Primary at 1 m through patient 0.002 mGy per
  film
• Public dose constraint lt 3 film per week
• Operator dose constraint lt 10 film per week
• Scatter at 1 m from patient 0.0005 mGy per film
• Public dose constraint lt 12 film per week
• Operator dose constraint lt 40 film per week.

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fin