Radiation Hazards, Effects &
Risks
Radiation Protection for X-ray Technologists
Dr Tim Wood
Clinical Scientist
Overview
• A little bit of history
– The discovery of radiation and health effects
– A bit of radioactive quackery c1920
• The mechanisms of radiation injury
– The Physics/Biology of radiation induced effects
– What is radiation dose?
– Deterministic and stochastic effects (with examples – not for
the squeamish)
• So how big are the risks?
– Where do we get our data from?
– Putting risk into context
– Why do we need to worry about radiation dose in dentistry?
A little bit of history…
The discovery of radiation
• Wilhelm Röntgen discovered
X-rays on 8th Nov 1895.
• Took first medical X-ray of
wife’s hand (22nd Dec 1895).
• Used to diagnose Eddie
McCarthy’s fractured left
wrist on 3rd Feb 1896 (20
min exposure).
• Awarded first Nobel Prize in
Physics in 1901 for his
discovery of ‘Röntgen rays’.
The discovery of radiation
• Henri Becquerel
discovered radioactivity on
26th Feb 1896.
The discovery of radiation
• In 1903 he shared
the Nobel Prize for
Physics with Pierre
and Marie Curie
who had refined
Becquerel’s work
and discovered the
existence of
Radium.
Then just as quickly…
• Late 1896
• Elihu Thomson – First person
to prove a direct relation
between exposure and health
effects.
• Deliberately exposed left
index finger for half an hour a
day for several days –
resulted in erythema, swelling
and pain.
Then just as quickly…
• Late 1896
• Edison’s assistant – hair fell
out & scalp became inflamed
& ulcerated.
• Several reports of ill-effects on
the eyes – result of direct
viewing of fluorescent
screens.
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.
Sister Blandina (1871-1916)
• 1898 – Radiographer in Cologne.
• Held nervous patients & children
with unprotected hands.
• 6 months later had cancer of hand
– arm amputated.
• 1915 – severe breathing difficulties.
• Extensive shadow on the left side of thorax.
• Large wound on her whole front- and back-side.
• Died 22nd Oct 1916.
Mihran Kassabian (1870-1910)
• Was a medical missionary
student and photographer
who became one of the
most prominent pioneering
radiologists of the time.
• By 1898 he had become
an American citizen
Mihran Kassabian (1870-1910)
The literature c1901…
• Rollins W. X-light kills. Boston Med Surg J
1901;144:173.
• Codman EA. No practical danger from the xray. Boston Med Surg J 1901;174:197
But by 1913…
• Dental office.
• Lead glass shield around the tube (but none
around the high voltage wires!).
Radioactive quackery
• 1903 – J. J. Thomson identifies radioactivity
(Radon) occurring naturally in well water.
• c1910 – Radioactive health springs cured
everything (apparently)…
• 1912 – The Revigator was
launched to provide
radioactive water at home.
• Many other products followed.
– drinks, inhalers, etc.
Radioactive quackery
• c1920-1930 – Radium became the alternative to
Radon with all manner of products available.
– e.g. salves, beauty creams, toothpaste, ear-plugs,
chocolate bars, bread, soaps, suppositories and
contraceptives.
And now for a bit of Physics/Biology…
Mechanisms of Radiation Injury
• LD(50/30) = 4 Gy
– The dose required to kill 50% of test cohort in 30 days.
 280 J to 70 kg man.
 1 milli-Celsius rise in body temp.
 drinking 6 ml of warm tea.
i.e. the damage is not caused by heating,
but ionisation.
Ionising Radiations
• Have the ability to
separate electrons from
atoms to produce ‘ions’
– X-rays
– Gamma rays (-rays)
– Beta particles ()
– Electron beams

X-ray passes
straight through cell
No change to cell

X-ray causes a
chemical reaction in
cell, but no damage
done or damage
repaired by cell
No change to cell

DNA damaged in a
“fatal” way”
Cell killed

DNA damaged,
causing cell to
reproduce
uncontrollably
Cancer?
Damage depends on a number
of factors:
• The type and number of nucleic acid
bonds that are broken.
• The intensity and type of radiation.
• The time between exposures.
• The ability of the cell to repair the
damage.
• The stage of the cell’s reproductive cycle
when irradiated.
What is radiation dose?
• Absorbed Dose (Jkg-1 or Gy)
– Amount of energy deposited per kilogram.
– Dose to an organ or tissue.
• DOSE TO A CERTAIN PLACE IN THE BODY
RADIATION
TISSUE
• Effective Dose (Jkg-1 or Sv)
– This is the average dose to the whole body.
– This gives us the risk of contracting cancer due to the
X-ray exposure.
• OVERALL DOSE TO THE WHOLE BODY
Deterministic effects of Ionising
Radiation
• Where very large doses kill many cells
– Radiation ‘burns’.
– Cataract.
– Radiation sickness.
• Deterministic effects
– Caused by significant cell necrosis.
– Not seen below a threshold dose.
– Will definitely be seen above a threshold dose.
– Above the threshold, the bigger the dose, the
worse the effect.
5000
5000
3500
3000
2500
2000
2000
STAFF
DOSES
NEVER THIS
BIG!
3000
milli-Gray
6000
4000
500
500
500
1000
50
150
0
1 min fluoro
skin dose
Fetal death
Temp. male
sterility
B. marrow
supression
Lens damage
Transient
erythema
Female
sterility
Temp.
epilation
Perm. male
sterility
Cataracts
Hair loss from CT scan
(Imanishi et al 2005)
• 53-year-old woman with subarachnoid haemorrhage.
• 4 CT perfusion scans and two angiographies of the head performed within
first 15 days of admission .
• Bandage-shaped hair loss 37 days after first CT lasted for 51 days.
2 embolisations – hair loss after each procedure.
13 x 10 cm area.
Re-grew after 4 months.
Dose estimate >3 Gy.
Interventional Cardiology
• 40 year old male
• 4 procedures on one day 29th March 1990
– Coronary angiography
– Coronary angioplasty
– Second angiography due to complications
– Coronary artery by-pass graft
Probably >20 Gy.
Extreme case!
6-8 weeks
16-21 weeks
18-21 months
Close up of previous
Post-skin graft
49-year-old man who underwent two transjugular intrahepatic portosystemic shunt
(TIPS) placements and one attempted TIPS placement within a week
6 months – secondary ulceration
with surrounding rings of de- and
hyperpigmentation.
7.5 months – small blisters
developed. Wound is very
painful.
10 months – wound has
progressed in size and depth.
22 months – non-healing ulcer
with exposure of deep tissues,
including spinous process of
vertebra.
23 months – musculocutaneous
skin grafting was performed.
Disfigurement is permanent.
Koenig, T. R. et al. Am. J. Roentgenol. 2001;177:3-11
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 (but no
more severe).
Cancer risks
• It is assumed that any dose of radiation could
potentially cause cancer.
50%
%
40%
30%
20%
10%
0%
0
•
500
1000
1500
mSv
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.
Attributable lifetime risk,
% per sievert
Attributable lifetime risk of fatal cancer
depending on age at exposure
Age at time of exposure
So how big are the risks?
Radiation Effects
• Acute radiation syndrome
– Including vomiting, diarrhoea,
reduction in the number of blood
cells, bleeding, epilation (hair loss),
temporary sterility in males, and lens
opacity (clouding)
• Late 1940’s Dr Takuso Yamawaki
noted an increase in leukaemia
– 20% of radiation cancers were
leukaemia (normal incidence 4%)
– Incidence peaked at 6-8 years
• Solid cancers – excess seen from
10 years onwards.
Cancer deaths between 1950 and 1990 among Life
Span Study survivors with significant exposure
(i.e. > 5 mSv or within 2.5 km of the hypocentre)
Number of
Dose range
cancer
deaths
Estimated
excess death
Attributable
fraction
5 - 200 mSv
3391
63
2%
200 - 500 mSv
646
76
12 %
0.5 - 1 Sv
342
79
23 %
> 1 Sv
308
121
39 %
All
4687
339
7%
Atomic Bomb Survivors 1990
49,000
30,000
430
7570
Still alive in 1990
Non-cancer death
"Natural" cancer death
Radiation induced cancer death
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.
Hereditary Effects
• Observed in animal experiments.
• Not observed in A-bomb victims.
• ICRP Detriment for severe hereditary
disease = 1.3 x 10-5 [1 in 77000] per mSv.
– (i.e. approx 1/4 fatal cancer risk).
Pregnancy - Radiation Risks
Age
(weeks)
0-1
Minimal dose (mGy) for:
Lethality
Gross malformation
Mental retardation
No threshold at day 1?
No threshold at day 1?
No effects observed
about 8 weeks
100 thereafter
2-5
250-500
200
5-7
500
500
7-21
> 500
Very few observed
Weeks 8-15: No
threshold?
Weeks 16-25: Threshold
dose 600-700
To term
> 1000
Very few observed
Weeks 25-term: No effects
observed
ICRP risk factors
Detriment per mSv
Exposed Population
Adult workers
Whole population
Foetus
Fatal cancer
Non-fatal cancer
Severe hereditary
effects
Total
4.0 x 10-5
0.8 x 10-5
0.8 x 10-5
5.6 x 10-5
1 in 25000
1 in 125000
1 in 125000
1 in 18000
5.0 x 10-5
1.0 x 10-5
1.3 x 10-5
7.3 x 10-5
1 in 20000
1 in 100000
1 in 77000
1 in 14000
3.0 x 10-5
3.0 x 10-5
6.0 x 10-5
1 in 33333
1 in 33333
1 in 17000
Risks associated with X-rays
• Adult Exposure (per 1 mSv)
– Fatal cancer (all types)
– Fatal leukaemia
– Non fatal cancer
– Heritable effects
• Childhood exposure
– Fatal cancer
• Foetal exposure
– Fatal cancer to 15 years
– All cancers to 15 years
– Heritable effects
1 in 20,000
1 in 200,000
1 in 100,000
1 in 80,000
1 in 10,000
1 in 33,000
1 in 17,000
1 in 42,000
Average Risk of Death from Various Accidents (US)
Accident
Total
Individual Chance
Type
Number
Per Year
Motor Vehicle
55,791
1 in 4,000
(1 in 20000 UK)
Falls
17,827
1 in 10,000
Fires and Hot Substances 7,451
1 in 25,000
Drowning
6,181
1 in 30,000
Firearms
2,309
1 in 100,000
Air Travel
1,778
1 in 100,000
Falling Objects
1,271
1 in 160,000
Electrocution
1,148
1 in 160,000
Lightning
160
1 in 2,000,000
Tornadoes
91
1 in 2,500,000
Hurricanes
93
1 in 2,500,000
All Accidents
111,992
1 in 1,600
RELATIVELY SMALL DOSES
AND RISKS SO WHY
WORRY SO MUCH?
30 January 2004
700 CANCER CASES
CAUSED BY X-RAYS
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 eachX-ray
year can
attribute the disease
exposure.
X- risk
Average
examination
doseto =X-ray
0.5mSv
► Diagnostic
1 in 40,000
rays, which are used in conventional radiography and imaging techniques such
as CT scans,UK
are Radiology
the largest man-made
of radiation
to the
= 41.5source
million
X-rays exposure
per year
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.
Largest exposure from manmade radiation is medical
>41.5 million medical & dental x-rays in UK
annually
49
Everyday non-occupational
exposure
• Effective dose from natural background radiation
in the UK is approximately 2.3 mSv
• This natural radiation comes from cosmic rays,
rocks and soil, food, human body & radon.
Why is radiation potentially
dangerous when to workers
who are not exposed to the
primary beam?
X-ray Tube
Primary Beam
Scattered Radiation
Patient
Staff
How to reduce occupational exposure – the
principles of radiation protection
management
There are three principles of radiation protection:
•
Justification
–
All exposures to ionising radiations must be clinically justified –
benefit must outweigh detriment
•
Optimisation
–
Once exposure has been justified it must be optimised i.e.
lowest possible dose for acceptable image quality
•
Limitation
–
Radiation workers are subject dose limits by law
Practical means of reducing
exposure
· Time
· Distance
· Shielding
Shielding
Shielding
Typical transmission through
shielding at 90 kVp
•
•
•
•
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%.
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