Lecture 1
description
Transcript of Lecture 1
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Radiation Protection for Cardiologists
John SaundersonRadiation Protection AdviserPRH ext 6690
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Plan
• 3 afternoons of lectures (30/1/04, 13/2/04, 26/3/04)
• 1 afternoon in Cath Lab with phantoms and dosemeters (2/4/04)
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Radiation Protection?
• The law – IRMER – “adequate training”
• Higher Medical Training Curriculum for Cardiology – April 2003
• Angiography = 0.8% of X-ray procedures, but 10% of X-ray dose
• Radiation can be dangerous
Why bother?
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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 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.
30 January 2004
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Syllabus• Physics & hazards of ionising radiation to
patients & staff• Statutory requirements for Medical
Exposures• Equipment• Factors affecting patient & staff dose• Important aspects of cardioradiology
• Above covers IRMER “Core of Knowledge”.
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www.hullrad.org.uk
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Radiation Hazards
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Wilhelm Roentgen
• Discovered X-rays on 8th November 1895
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Henri Becquerel
• Discovered radioactivity on 26 February 1896
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Frau Roentgen’s hand, 1895
Colles’ fracture 1896
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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
Edison’s assistant - hair fell out & scalp became inflamed & ulcerated
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Mihran Kassabian (1870-1910)
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Sister Blandina (1871 - 1916)
1898, started work as radiographer in Cologne
held nervous patients & children with unprotected hands
controlled the degree of hardness of the X-ray tube by placing her hand behind of the screen.
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Sister Blandina
After 6 months strong flushing & swellings of hands
diagnosed with an X-ray cancer,
some fingers amputated
then whole hand amputated
whole arm amputated.
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Sister Blandina
1915 severed difficulties of breathing
extensive shadow on the left side of her thorax
large wound on her whole front- and back-side
Died on 22nd October 1916.
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First Radiotherapy TreatmentEmil Herman Grubbé
• 29 January 1896
• woman (50) with breast cancer
• 18 daily 1-hour irradiation
• condition was relieved
• died shortly afterwards from metastases.
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Radiotherapy 1899Basal Cell Carcinoma
A) Before B) 30 years on
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William Rollins
• Rollins W. X-light kills. Boston Med Surg J 1901;144:173.
• Codman EA. No practical danger from the x-ray. Boston Med Surg J 1901;144:197
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Early Protective Suit
•Lead glasses
•Filters
•Tube shielding
•Early personal “dosemeters”
•etc.
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Protection Progress
• 1898 Roentgen Society Committee of Inquiry
• 1915 Roentgen Society publishes recommendations
• 1921 British X-Ray and Radiation Protection Committee established and reported
• 1928 2nd International Congress of Radiology adopts British recommendations + the Roentgen
• 1931 USACXRP publishes first recommendations (0.2 r/d)
• 1934 4th ICR adopts 0.2 Roentgens per day limit
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Life Span Study
• About 94,000 persons, • > 50% still alive in 1995• By 1991 about 8,000 cancer deaths 430 of these attributable to radiation• 21 out of 800 in utero with dose > 10
mSv severely mentally retarded individuals have been identified
• No increase in hereditary disease• http://www.rerf.or.jp/eigo/glossary/lsspopul.htm
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Mechanisms of Radiation Injury
• LD(50/30) = 4 Gy280 J to 70 kg man1 milli-Celsius rise in body temp.drinking 6 ml of warm tea
i.e. not caused by heating, but ionisation.
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Radiation Quantities and Units
• Absorbed dose • Equivalent dose• Effective dose• others .
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Absorbed Dose (D)
• Amount of energy absorbed per unit mass [D=d/dm]
• 1 Gray (Gy) = 1 J/kg• Specific to the matierial, e.g.
– absorbed dose to water– absorbed dose to air– absorbed dose to bone.
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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)
• Typical 1 minute screening = 20 mGy skin dose
• Chest PA = 160 uGy skin dose• Threshold for transient erythema = 2
Gy .
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Equivalent Dose (HT,R)
• Absorbed dose to tissue x radiation weighting factor [HT,R = wR.DT,R]
• Units are Sieverts (Sv)– All photons, electrons and muons, wR = 1– Neutrons, wR = 5-20 (depending on energy)– Protons, wR = 5– Alpha particles, wR = 20
• For X-rays and gamma rays, 1 Gy = 1 Sv• For beta particles and positrons, 1 Gy = 1 Sv• For alphas, 1 Gy = 20 Sv .
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Effective Dose (E)
• Sum of equivalent doses to each tissue/organ x organ weighting factors [E = T wT.HT]
• Units are Sieverts (Sv)
Tissue or organ wT
Gonads 0.20Red bone marrow 0.12Colon 0.12Lung 0.12Stomach 0.12Bladder 0.05Breast 0.05Liver 0.05Oesphagus 0.05Thyroid 0.05Skin 0.01Bone surfaces 0.01Remainder 0.05
e.g. if gonads alone received 2 Gy to tissue, E = 0.20 x 2 = 0.4 Sv.
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Typical Values of E
• Pulmonary angiography = 5.4 mSv• CT abdomen = 10 mSv• Conventional abdomen X-ray = 1 mSv• Chest PA = 20 uSv• Annual dose limit for radiation workers = 20
mSv• Annual background dose = 2.5 mSv
• (risk of inducing cancer or hereditary disease is proportional to Effective Dose) .
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Others• Dose area product (Gy.cm2) - dose x field size
• Collective dose (manSv) - effective dose x number of people exposed (e.g.Angiography gave 1,923 manSv in UK in 2000)
• Exposure (R or C/kg) - charge produced in 1 kg of air• Air kerma (Gy) - energy released in 1 kg of air (dose meters
usually read in air kerma)• Dose equivalent (Sv) - superseded by equivalent dose • Effective dose equivalent (Sv) - superseded by effective
dose• Ambient dose equivalent (Sv) - dose a particular depth
(often used for personal dosimeter results)• CTDI (mGy), DLP (mGy.cm)• Committed effective dose (Sv) – from ingested
radionuclides over 50 y .
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Old Units
• 100 rad = 1 Gy = 100cGy• 100 rem = 1 Sv• 100 R 0.9 Gy
Main Units for Cardiology• Effective dose in mSv • Skin dose in mGy or mSv• DAP in Gy.cm2
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Two Types of Effect
•Deterministic effects (“threshold effects”)
•Stochastic effect (“chance effects”) .
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Deterministic Effects• Caused by significant cell necrosis
• Not seen below a threshold dose
• Above the threshold, the bigger the
dose, the worse the effect
• Do not accumulate over long term .
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5000
3500
3000
2500
2000
500 500150
500
500
1000
2000
3000
4000
5000
6000
Cataracts
Perm
. male
sterility
Temp.
epilation
Fem
alesterility
Transienterythem
a
Lens damage
B. m
arrowsupression
Temp. m
alesterility
Fetal death
1 min fluoro
skin dose
mill
i-Gra
y
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From FDA, Sept 1994, “Avoidance of serious x-ray induced skin injuries to patients during fluoroscopically-guided procedures”
Effect ThresholdFluoroscopy time to reach threshold Time to
onset ofDose Typical fluoro. dose
rate of 20 mGy/minHigh-level dose rate
of 200 Gy/mineffect
Early transient erythema 2 Gy 1 hr 42 min 10 min hours
Temporary epilation 3 Gy 2½ hr 15 min 3 weeks
Main erythema 6 Gy 5 hr 30 min 10 days
Permanent epilation 7 Gy 6 hr 35 min 3 weeks
Dry desquamation 10 Gy 8 hr 50 min 4 weeks
Invasive fibrosis 10 Gy 8 hr 50 min
Dermal atrophy 11 Gy 9 hr 55 min > 14 wks
Telangiectasis 12 Gy 10 hr 1 hr > 52 wks
Moist desquamation 15 Gy 12½ hr 1 hr 15 min 4 weeks
Late erythema 15 Gy 12½ hr 1 hr 15 min 6-10 wks
Dermal necrosis 18 Gy 15 hr 1 hr 30 min > 10 wks
Secondary ulseration 20 Gy 17 hr 1 hr 40 min > 6 wks
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Example of Radiation Injury in Cardiology
•40 year old male
•coronary angiography
•coronary angioplasty
•second angiography procedure due to complications
•coronary artery by-pass graft
•all on 29 March 1990 .
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Fig. A6-8 weeks after multiple coronary angiography and angioplasty procedures
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Fig. B16 to 21 weeks after procedure, with small ulcerated area present
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Fig. C18-21 months after procedure, evidencing tissue necrosis
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Fig. DClose up of lession in Fig. C
From injury, dose probably in excess of 20 Gy .
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Fig. EAppearance after skin grafting procedure .
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75-year-old woman with 90% stenosis of right coronary
artery. Photograph of right lateral chest obtained 10 months after percutaneous transluminal coronary angioplasty shows area of hyper- and hypopigmentation, skin atrophy, and
telangiectasia (poikiloderma)
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56-year-old man with obstructing lesion of right coronary artery.
Photograph of right posterolateral chest wall at 10 weeks after
percutaneous transluminal coronary angioplasty shows 12 x 6.5 cm hyperpigmented plaque with hyperkeratosis
below right axilla
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49-year-old woman with 8-year history of refractory supraventricular tachycardia. Photographs show sharply demarcated erythema above right elbow at
3 weeks after radiofrequency cardiac
catheter ablation
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48-year-old woman with history of diabetes mellitus and severe coronary artery disease who
underwent two percutaneous transluminal coronary angioplasties and stent placements within a month. Photograph of left mid back 2 months after last procedure shows well-marginated focal erythema and desquamation
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69-year-old man with history of angina who underwent two angioplasties of left coronary artery within 30 hr. Photograph taken 1-2 months after last procedure shows secondary ulceration over left scapula
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To prevent deterministic effects
• Keep skin dose below 2 Gy
• Keep eye dose below 500 mGy .
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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. > 5 mSv or within 2.5 km of the hypercentre)
Dose range Number of
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 %
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Fraction of cancers induced by radiation
0%
10%
20%
30%
40%
50%
0 500 1000 1500
mSv
%
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Fraction of cancers induced by radiation
0%
10%
20%
30%
40%
50%
0 500 1000 1500
mSv
%
Risk of inducing fatal cancer = 5 x 10-2 Sv-1
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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
Detriment per mSv
Exposed Population Fatal cancer Non-fatal cancer Severed hereditaryeffects
Total
Adult workers 4.0 x 10-5 0.8 x 10-5 0.8 x 10-5 5.6 x 10-5
Whole population 5.0 x 10-5 1.0 x 10-5 1.3 x 10-5 7.3 x 10-5
(fetus 3.0 x 10-5 3.0 x 10-5 6.0 x 10-5)
5.0 x 10-5 per mSv 1 in 20,000 chance .
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Pregnancy - Radiation Risks
Age Minimal dose (mGy) for:
(weeks) Lethality Gross malformation Mental retardation
0-1 No threshold at day 1? No threshold at day 1?
100 thereafter No effects observed to
2-5 250-500 200 about 8 weeks
5-7 500 500
7-21 > 500 Very few observed Weeks 8-15: nothreshold?
Weeks 16-25: thresholddose 600-700 Gy
To term > 1000 Very few observed Weeks 25-term: no effectsobserved
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Total risk of cancer up to age 15 years following in utero exposure (per mGy)
Cancer type Fatal Non-fatal Total
Leukaemia 1.25 10-5 1.25 10-5 2.5 10-5
Other 1.75 10-5 1.75 10-5 3.5 10-5
Total 3.0 10-5 3.0 10-5 6.0 10-5
at 8-15 weeks it is estimated that 30 IQ points are lost per 1000 mGy. Risk of heritable effects estimated at 2.4 10-5 per mGy
"Natural Risks"
Heritable disease 1 10-2 to 6 10-2
Fatal cancer to age 15 years 7.7 10-4
Lifetime cancer risk 20 10-2 to 25 10-2
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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 CardiologyTaken from “Real-time quantification and display of skin radiation during coronary angiography and intervention”, den Boer A, et al., Oct 2001
•332 patients
•25 - 99 Gy.cm2 dose-area product
•4 - 18 mGy effective dose
•1:5000 - 1:1100 risk of inducing fatal cancer .
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Dose Area Product
•Stochastic risks approx. proportional to DAP•Skin dose is DAP / area irradiated•1 Gy.cm2 3 mGy skin dose
•1 Gy.cm2 0.2 mSv effective dose .
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DAP meter reading(Gy.cm2)
Risk to patient
50 About 1 in 2000 risk of inducing fatal cancer
100 About 1 in 1000 risk of inducing fatal cancer
200 About 1 in 500 risk of inducing fatal cancer
400 About 1 in 250 risk of inducing fatal cancer
There is a risk of early transient erythema if the same area of skin isexposed (onset a few hours after exposure)
1100 About 1 in 91 risk of inducing fatal cancer
There is a risk of main erythema, if same area of the skin is exposed(onset about 10 days after exposure)
20/11/96
2 Gy erythema threshold 666 Gy.cm2 DAP (v. approx!!)
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“Small” risks so why worry?
• Average effective dose for angiography = 6 mSv
• Risk of fatal cancer from 6 mSv only 1 in 3,300
• But, large number of patients– 321,174 angiography procedures in 2000– Therefore, high probability that radiation from
angiography will kill some patients
• So– All exposures must be JUSTIFIED– Doses to patients, and staff, must be As Low As
Reasonably Achievable (ALARA principle) .
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Still to do
• Production and interaction of X-rays
• Image formation• Dose reduction – patients and staff• Legislation and guidelines• Equipment
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fin