Radiation Kilo Curie

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Do not adjust your set
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Radiation Protection for Dentists

• John Saunderson,
• Radiation Protection Adviser

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IRMER Syllabus

• Production of X-rays
• Absorption and scatter
• Radiation hazards and dosimetry
• Special attention areas
• Radiation Protection
• Laws Guidelines
• Equipment .

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Radiation Hazards Dosimetry
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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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Fig. C 18-21 months after cardiology procedure,
evidencing tissue necrosis
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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 mSv
• Two intraoral dental films give about 0.005 mSv.

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Tissue Reactions(Deterministic effects)Very
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, it is likely that radiation from
  dental 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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Radiation Protection for Dentists
Part 2 The Nature of Ionising Radiation

• John Saunderson
• Radiation Protection Adviser
• PRH ext 6690

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Ionising or Non-Ionising?

• Ionising radiation
• X-rays
• Gamma rays
• Beta particles
• Positrons, electrons
• Alpha particles
• Neutrons
• Pions, etc.

• Non-ionising
• Ultrasound
• MRI
• Lasers
• Ultraviolet
• Infra-red.

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Types of Ionising Radiation

• Electromagnetic
• X-rays
• Gamma rays
• Beta particles
• Annihilation radiation

• Particles
• Beta particles
• Positrons, electrons
• Alpha particles
• Neutrons
• Pions, etc.

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Electromagnetic Spectrum
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X-rays

• Electromagnetic radiation
• Short wave length
• 90 kV beam from 1.4 x 10-11 m (1/10th atom width)
• High frequency
• 2.2 x 1019 Hz (22 billion GHz)
• Photons
• 1.4 x 10-14 J (90 keV)

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Production of X-rays
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99 electron energy wasted as heat .
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Effect of Tube Currant (mA) and Tube Voltage (kV)

• mA effects number of electrons per second,
  therefore number of x-ray photons per second
• mAs effects total number of x-ray photons
• kV effects how much energy the photons have, and
  how many per second.

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Processes for X-ray production

• Bremsstrahlung
• Characteristic radiation

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Bremstrahlung radiation

• braking radiation
• ve nucleus attracts ve electron and slows it
  down
• Energy lost as a photon
• Produces continuous spectrum from zero to e x kV.

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Characteristic Radiation

• Incoming electron knocks an orbital electron out
  of orbit (1,2)
• An electron falls from a higher level into the
  gap (3)
• The energy lost in falling is released as a
  photon (4)
• Energy depends on target material
• i.e. characteristic of the target.

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80 kVp Diagnostic X-ray Beam
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Changing Beam Quality Intensity

• Tube voltage (kV)
• Tube current (mA)
• Exposure time
• Voltage rectification
• Cone length.

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Effect of different tube voltages (kV)
Through 2cm soft tissue

• 50 kV, T 33
• 70 kV, T 40

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Effect of different tube current (mA)
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Effect of filtration
Through 2cm soft tissue

• 0mmAl, T 21
• 1.5mmAl, T 40
• 2.5mmAl, T 45

Dental sets up to 70 kV must have at least 1.5 mm
aluminium
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Effect of filtration
Dental above 70 kV must have at least 2.5 mm
aluminium

• T1.5mmAl45
• T2.5mmAl50

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Tube to Patient Distance
20cm cone gives 30 lower dose to skin than 10cm
cone for same film dose
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Self-rectified or DC

• DC higher intensity
• DC higher average photon energy.

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Parameter Summary

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

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Attenuation, Scattering and Absorption
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Attenuation, Scattering, Absorption
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No attenuation - adds to contrast .
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Absorption - adds to contrast .
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Scattering - adds to contrast, if it misses
imager .
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Scattering - adds to fog, if it hits imager .
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Attenuation is absorption scatter

• Absorption adds to contrast
• Scatter can add to contrast, but can also add to
  fog .

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How attenuation varies

• Different x-ray energies
• Different materials

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Photoelectric effect
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Photoelectric Absorption

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

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Compton Scattering
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Compton Scattering

• ? ? ?m x ?e / E
• ? linear attenuation coefficient for PE effect
• ?m mass density (kg/m3)
• ?e electron density (e- per kg)
• E photon energy

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Effect of X-ray photon energy
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X-ray photon energy
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Different Materials (70 kVp)

• 1 cm of soft tissue ? 66 transmitted
• 1 cm bone ? 17 transmitted
• 1 cm tooth ? 6 transmission
• density, atomic number

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Density

• grams per c.c.
• Bone 1.85 g/cm3
• soft tissue 1 g/cm3
• tooth 2.4 g/cm3

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Atomic number

• Property of atoms of different elements

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Atomic number (Z)

• Property of atoms of different elements
• Absorption proportional to Z3
• Calcium Z 20
• Hydrogen Z 1 oxygen Z 8
• so water (H2O) Z (118)/3 31/3
• so calciumwater 203 31/33 2161
• BUT scattering not affected by Z

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Effect of increasing kV

• Higher average photon energy
• Less attenuation
• Greater proportion of scatter
• Less dependant on atomic number .

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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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Tube Voltage (kV)

• Higher kV lower patient dose
• e.g. changing from 50 to 70 kV leads to 18
  reduction in skin dose
• Higher kV less contrast
• e.g. changing from 50 to 70 kV reduces 1 cm
  bone/ 1 cm soft tissue contrast by 0.3.

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Filtration

• More filtration lower patient dose
• from 1.5 to 2.5mm Al ? ? 11 skin dose
• More filtration less contrast
• from 1.5 to 2.5mm Al ? ? 1cm bone/ 1 cm soft
  tissue contrast by 0.8.

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Tube to Patient Distance

• Greater FSD lower patient dose
• e.g. ? from 10 to 20 cm ? ? 30 skin dose
• Greater FSD less magnification
• (so fewer distortions).

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Radiation Protection for Dentists
Part 3 Practical Protection for Patients Staff

• John Saunderson
• Radiation Protection Adviser
• PRH ext 6690

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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 (cone length)
• Film speed
• 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.

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Tube Voltage (kV)

• Higher kV lower patient dose
• 70kV gives about half the skin dose of 50kV
• (although less contrast)

Filtration

• More filtration lower patient dose
• (although less contrast)

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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

• Greater FSD lower patient dose
• Greater FSD less magnification (so fewer
  distortions).

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Film Speed

• Faster films require less radiation
• Therefore, faster films give less dose to
  patients
• e.g. E-speed film requires half the dose of
  D-speed film
• Good processing, and quality assurance is VITAL.

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Pregnancy

• In dental X-ray, dose to foetus is trivial
• Rare exception - vertex occlusal projection
• ask if patient may be pregnant
• record response
• if no, go ahead
• if yes, decide if x-ray can wait until after
  delivery
• if no, use lead rubber to shield pelvic area
• if maybe, is menstrual period overdue
• no - proceed
• yes - can x-ray wait until pregnancy confirmed
• See GN para2.40..

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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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• 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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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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Methods of Radiation Protection
Radiation protection of staff
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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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