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Radiation Hazards and Dosimetry

Dr. Craig Moore Medical Physicist & Radiation Protection Adviser Radiation Physics Service CHH Oncology

In the beginning ...

• Wilhelm Roentgen discovered X-rays on 8 th November 1895, and published his findings, "

On A New Kind Of Rays

" (

Über eine neue Art von Strahlen

), 50 days later on 28 December 1895 • Henri Becquerel discovered radioactivity on 26 February 1896

(“On the invisible rays emitted by phosphorescent bodies”. Comptes Rendus 122, 501–503, 1896)

First Human Radiograph

• Frau Roentgen’s hand • Not medical - possibly to show off expensive gold ring??

First US medical radiograph

• 3 rd February 1896 by Edwin Frost an astronomer at Dartmouth College, New Hampshire. • A boy who had injured his wrist was seen by Dr. Gilman Duboi Frost, Edwin’s brother.

• Edwin was asked to make the radiograph and produced the first image of a Colles fracture.

(Remember, 3 months earlier no-one knew that X-rays even existed. Neither FDA nor NICE approval were required at the time.)

X-rays became all the rage

Assumed to be no more harmful than light

Unshielded Glass X-ray tube “Fluoroscope” fluorescent screen inside black card Dr Rome Wagner & glamorous assistant

Early occupational exposures

• • • Early X-ray tubes were gas filled and needed time to warm up after switching on The X-ray pioneers took repeated X-rays of their own hands to see if the tube was ready for patients X ray tubes might be used like light bulbs to “illuminate” the room with X-rays

First Reports of Injury

• (Nov 1985 Roentgen discovered X-rays) • March 1896 - The Lancet - L R L Bowen, in a talk to the London Camera Club, warned that x-rays might produce effects like sunburn • In April 1896 - BMJ - L G Stevens reported that people exposed to x-rays suffered sunburn and dermatitis

Early example

In the summer of 1896 Herbert Hawks was demonstrating x-rays in Bloomingdale Brothers' Store in New York. Hawks, an assistant to Dr. Pupin at Columbia University, experienced radiation burns and received an unusual diagnosis “Mr. Hawks, during the afternoon and evening of each day for four days, was working around his apparatus for from 2-3 hours at a time. At the end of the four days, he was compelled to cease active work, owing to the physical effects of the x-rays upon his body. The first thing Mr. Hawks noticed was a drying of the skin, to which he paid no attention, but after a while it became so painful it was necessary to stop all operations. The hands began to swell and assumed the appearance of a very deep sunburn. At the end of two weeks the skin all came off the hands. The knuckles were especially affected, they being the sorest part of the hand. Among other effects were the following: the growth of the fingernails was stopped and the hair on the skin that was exposed to the rays all dropped out, especially on the face and sides of the head. The chest was also burned through the clothing, the burn resembling sunburn. Mr. Hawks' disabilities were such that he was compelled to suspend work for two weeks. He consulted physicians, who treated the case as one of parboiling.”

Association or Effect?

• • Hawks thought his injuries probably due to electrical effects, not X-rays Others suggested that such effects came from 1. the electric sparks in the high-voltage generator, 2. from ultra-violet (uv) radiation, 3. from chemicals used in developing plates, 4. from ozone generation in the skin and 5. from faulty technique

Mounting evidence and early safety tip

November 1896

Elihu Thomson purposely exposed the little finger of his left hand for half an hour close to an x-ray tube. Over a period of a week or two the finger became swollen, sensitive and painful. He was convinced that the effects were caused by the “chemical activity” of the rays and issued a caution. (One of his recommendations was “

Do not expose more than one finger

”)

Opinion was still divided

• Boston Medical & Surgical Journal, 1901 vol 144 • page 173 - Rollins W.

X-light kills

. • page 197 - Codman EA.

No practical danger from the x-ray

William Rollins As early as 1902 Rollins wrote almost despairingly, that his warnings about the dangers involved in careless use of x-rays was not being heeded, either by industry or by his colleagues. By this time Rollins had proved that x-rays could kill experimental animals

(inside a Faraday cage to prove it was not an electrical effect)

, could cause a pregnant guinea pig to abort, and that they could kill a foetus. He also stressed that "animals vary in susceptibility to the external action of X light" and warned that these differences be considered when patients were treated by means of x-rays (Wikipedia)

First fatality from artificial radiation?

Clarence Dally (glassblower & assistant to Thomas Edison, 1865 –1904) By 1900, Clarence Dally was suffering radiation damage to his hands and face sufficient to require time off work. In 1902, one lesion on his left wrist was treated unsuccessfully with multiple skin grafts and eventually his left hand was amputated. An ulceration on his right hand necessitated the amputation of four fingers.

These procedures failed to halt the progression of his carcinoma, and despite the amputation of his arms at the elbow and shoulder, he died from mediastinal cancer. Dally is thought to be the first American to die from the effects of experimentation with radiation. Following this, Thomas Edison abandoned his research on X rays. In 1903, a shaken Edison said “Don't talk to me about X-rays, I am afraid of them.

“ (Wikipedia) Glass X-ray tube in wooden box (to shield from high voltage electricity, not X-rays) “Fluoroscope” fluorescent screen inside black card (

The famous

) Thomas Edison

So, were the X-ray Pioneers idiots?

• We now know that a radiation dose of 4 Gray to the whole body will kill 50% of people within 30 days [ LD(50/30) = 4 Gy ], but – 4 Gray of energy is 4 Joules per kg – 4 Gy to whole body is enough to raise body temperature by only around 0.001

o C – i.e. less heating effect than a sip from a cup of hot tea • 19 th century scientists knew how much electrical energy they were using to make X-rays, so knew amount of energy was trivial • Cancer risk difficult to determine when “natural” incidence of cancer so high • Also, no knowledge of DNA and effect of ionisation on cell.

First Radiotherapy Treatment

Emil Herman Grubbé

• Not all bad news!

• 29 th January 1896 • Woman (50) with breast cancer • 18 daily 1-hour irradiation • Condition was relieved, although died shortly afterwards from metastases.

Aside

First Cardiac Catheterisation

• 1929 Werner Forßman – inserting cannula in vein in own arm, through which he passed a catheter for 65 cm – then walked to the X-ray department, where a photograph was taken of the catheter lying in his right – – auricle.

From Wikipedia -

In 1929, while working in Eberswalde, he performed the first human cardiac catheterisation. He ignored his department chief and persuaded the OR nurse in charge of the sterile supplies, Gerda Ditzen, to assist him. She agreed, but only on the promise that he would do it on her rather than on himself. However Forssmann tricked her by restraining her to the operating table and pretending to locally anaesthetise and cut her arm whilst actually doing it on himself. He anesthetized his own lower arm in the cubical region and inserted a uretic catheter into his antecubital vein, threading it partly along before releasing Ditzen (who at this point realised the catheter was not in her arm) and telling her to call the X-Ray department. They walked some distance to the X-ray department on the floor below where under the guidance of a fluoroscope he advanced the catheter the full 60 cm into his right ventricular cavity. This was then recorded on X-Ray film showing the catheter laying in his right atrium.

The head clinician at Eberswalde, although initially very annoyed, recognized Werner's discovery when shown the X-rays; he allowed Forssmann to carry out another catheterisation on a terminally ill woman whose condition improved after being given drugs in this way

Radiation Injury Recognised

• By 1910 most workers using X-rays and radioactive substances were taking some precautions such as – shielding the tube to produce a collimated beam – lead-rubber protective wear for operators – using a phantom hand to check tube rather than operator’s hand – filtering the beam to remove soft X-rays • Sadly too late for some. In 1936 a memorial stone was unveiled in Hamburg to 160 medical men, physicists, chemists, laboratory workers and nurses from 15 nations whose deaths were due to working with X-rays with the citation, “

They were heroic pioneers for a safe and successful application of x-rays to medicine. The fame of their deeds is immortal.”

• • • • • •

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 Roentgens per day) 1934 4th ICR adopts 0.2 Roentgens per day limit

Note,

• 0.2 Roentgens per day  500 millisieverts per year, which is the current legal skin dose limit.

• Risk of skin burns was well understood in early 20 th century • Whether radiation induced cancer was still a matter of debate

Radiation / Cancer link proven

Atomic Bombs

• Two A-bombs detonated above Hiroshima and Nagasaki, Japan in August 1945 • Within the first 4 months, the acute effects killed 90,000–166,000 people in Hiroshima and 60,000 –80,000 in Nagasaki, with roughly half of the deaths in each city occurring on the first day • Estimate of the total immediate and short term cause of death

Radiation Effects

• • Acute radiation syndrome Including vomiting, diarrhea, 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.

Ionising Radiation

• Ionising radiations – have the ability to separate electrons from atoms to produce “ions” +

-

Why is it dangerous?

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

Aside:

Quantifying Radiation, to quantifying the risk

Absorbed Dose (D)

• Amount of energy absorbed per unit mass [D=d  /dm] • 1 Gray (Gy) = 1 J/kg • Specific to the material, e.g.

– absorbed dose to water – absorbed dose to air – absorbed dose to bone • Can be relatively easily measured with a “dose meter”

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 m Gy entrance surface dose .

Different radiations, different risk

• 1 Gy of alpha particle radiation produced more tissue damage than • 1 Gy of neutron radiation, which produces more tissue damage than • 1 Gy of X-rays • Multiplying ABSORBED DOSE in Gy by a weighting factor (w R ) for the relative damage cause by different radiations gives us

EQUIVALENT DOSE

Equivalent Dose (H

T,R

)

• Absorbed dose to tissue x radiation weighting factor • • In mathematical notation – H T,R = w R .D

T,R – or if exposed a mix of radiations H T =  R w R .D

T,R (T = which tissue or organ you are considering; R = which type pf radiation) • Units are Sieverts (Sv)

Professor Rolf Sievert

(1896 – 1966) was a medical physicist whose major contribution was in the study of the biological effects of radiation.

Equivalent Dose (H T,R ) • H T,R

weighting factors, w

= w R .D

T,R • w R = 1 for – all photons (e.g. X-rays and gamma rays used in nuclear medicine), – electrons (e.g. beta particles used for nuclear medicine therapy and electron beams used in radiotherapy) and – muons (not used in medicine), • w R = 5-20 for neutrons,

(depending on energy)

• w R = 5 for protons (beginning to be used in radiotherapy) , • w R = 20 for alpha (  ) particles nuclear medicine therapy) , (recently used for palliative • e.g. for X-rays 1 Gy = 1 Sv, but for alpha particles 1 Gy = 20 Sv .

Equivalent Dose example of use

• Legal dose limits for skin or lens of eye exposure are expressed as EQUIVALENT DOSE – lens of eye limit for radiation workers = 150 mSv equivalent dose per calendar year – Limit for any 1 cm 2 of skin of radiation workers = 500 mSv equivalent dose per calendar year

Different organs or tissues, different risk

• 1 Sv equivalent dose to the lung is more likely to induce cancer than • 1 Sv equivalent dose to the thyroid, which is more likely to induce cancer than • 1 Sv equivalent dose to the brain • Also, 1 Sv to whole body is more likely to induce cancer than 1 Sv just to the head, etc.

• We need a quantity which is proportional to the overall risk of inducing cancer -

EFFECTIVE DOSE

Effective Dose (E)

• Sum of equivalent doses to each tissue/organ x organ weighting factors w T • E =  T w T .H

T • Units are Sieverts (Sv) • You need to know the dose to each organ/tissue of interest.

ICRP Publication 103 (2007)

tissue weighting factors

• w T = 12% for red bone marrow, breast, colon, lung, stomach, • w T = 8% for gonads • w T = 4% for liver, oesophagus, thyroid, bladder • w T = 1% for skin, bone surfaces, brain, salivary glands • w T = 12% for average dose to remainder tissues adrenals, extrathoracic region, gall bladder,

heart

, kidneys, lymphatic nodes, muscle, oral mucosa, pancrease, prostate, small intestine, spleen, thymus, uterus/cervix

Example of effective dose

• Abdomen PA radiograph • 80 kVp • 2.5 mm Al filtration • 75 cm FSD • 35 x 43 cm film • 5.4 mGy entrance skin dose •From this data computational models can be used to calculate the organ doses for an average man/woman •Weighting factors can be applied •The results added together give us

EFFECTIVE DOSE

Tissue or Organ

Ovaries Testes Lungs Stomach Colon RBM Thyroid Breasts Oesophagus Liver Urinary bladder Skin Total bone Brain Salivary glands Average remainder Organ dose, H T (mSv) 0.805

0.079

Weighting Factor, w T 0.04

0.04

0.037

0.417

0.718

0.599

0.000

0.007

0.042

0.518

0.450

0.386

0.697

0.000

0.472

0.12

0.04

0.12

0.04

0.01

0.12

Effective dose =  T w T .H

T H T x w T (mSv) 0.032

0.003

0.004

0.050

0.086

0.072

0.000

0.001

0.002

0.021

0.018

0.004

0.007

0.000

0.057

0.36 mSv

What’s effective dose for?

• Organ doses ranged – from 0.00 mSv (brain, thyroid) – to 2.97 mSv (kidneys) • Effective dose was 0.36 mSv • Risk of inducing cancer  risk of 0.36 mSv to all organs/tissues .

Effective dose example • Effective dose calculated for abdomen PA radiograph = 0.36 mSv • Therefore, risk of cancer from abdomen PA is the same as an equivalent dose of 0.36 mSv to the whole body

Typical Values of E (X-ray examinations)

• Barium enema = 7 mSv • CT abdomen = 10 mSv • Conventional abdomen = 1.0 mSv • Chest PA = 20 m Sv • Pulmonary angiography = 5.4 mSv • Annual effective dose limit for radiation workers = 20 mSv • Annual background dose = 2.5 mSv .

How do we apply this to Nuclear Medicine?

Concept of Absorbed Dose in Nuclear Medicine

The calculation of the absorbed dose - a tricky problem, because of several factors: – 1. the distribution of the radionuclide body and its uptake in certain within the critical organs – 2. inhomogeneous distribution of the nuclide even within the critical organ – 3. the biological half-life of the nuclide, which may vary with patients' ages and may be modified by disease or pathological conditions.

Absorbed dose to an organ is determined by:

•Radionuclide •Activity administered •Activity in the organ •Size and shape of the organ •Activity in other organs •Kinetics of radiopharmaceutical •Quality of radiopharmaceutical

• • • • •

The MIRD System of Internal Absorbed Dose Calculation

MIRD - Medical Internal Radiation Dosimetry developed by the Society of Nuclear Medicine The organ containing the radionuclide is called the source organ – this accumulates the activity We wish to calculate the absorbed dose to the organ – target this is irradiated by activity in the source organ The source and target organs may be the same The amount of radiation from the source reaching the target must be known

Derivation of the General MIRD Equation

• Let E be the mean energy per particle (photon or electron) • If n is the number of particles emitted per disintegration • then nE is the mean energy emitted per disintegration

Absorbed Dose

• Energy absorbed in a material per unit mass • Has unit of the gray (1 Gy = 1 J/kg)

Absorbed Dose in the Target Organ

The absorbed dose will be equal to the total amount of energy that is emitted by the source organ

the fraction of that energy that is absorbed in the target organ divided by the mass of the target organ

Absorbed Fraction

• The absorbed fraction, Φ, is the fraction of the energy emitted by the source organ that is absorbed in the target

Target Organ Source Organ

Absorbed Fraction

• Depends on – – – – the size of the source organ the size of the target organ the relative positions in the body of these organs the energy of the photons – the attenuation properties of the tissues between the source and target organs

Examples of Absorbed Fractions

Note:

= 1 for charged particles

Determination of the Absorbed Fraction

The only method available is CALCULATION using Monte Carlo modelling

What is Monte Carlo Modelling?

• Essentially a ray tracing method, in which the fates of individual particles are determined • The method is based on randomly sampling a probability distribution for each successive interaction • Typically, the history of 10 million photons will be modeled • All done on a computer!!!!! 

Determination of the Absorbed Fraction

• • • • Radiation will be emitted randomly by the source in all directions Some photons will escape from the body without interaction Some photons will deposit their energy by photo electric interactions Some photons will undergo Compton scattering

The MIRD Standard Man MIRD Pamphlet No. 5 Revised.

J Nucl Med 1978 Jan

The MIRD Standard Man MIRD Pamphlet No. 5 Revised.

J Nucl Med Jan 1978

Derivation of the General MIRD Equation

• If A is the activity of the source, the

cumulated activity

Ã is the sum, or accumulation, of all the nuclear transitions occurring in the source over a period of time • Ã = ∫A(t) • then ÃnE is the total radiation energy emitted by the source

Derivation of the General MIRD Equation

• ÃnE f is the energy absorbed in the target organ during the time interval of interest ( f is the absorbed fraction) • D = ÃnE f /m is the absorbed dose in the target organ, where m is the mass of the target organ

Derivation of the General MIRD Equation

D = ÃS (S = nE

/m)

S is dependent on the radionuclide and the geometry. S-values for different radionuclides and source/target organs can be found in MIRD publications

Derivation of the General MIRD Equation

Generally each radionuclide will emit more than one type of

“

particle

”

D = Ã  S i factor of the i th where S i particle is the S

Derivation of the General MIRD Equation

Generally there will be many source organs r h contributing to the target organ r organ.

k , and all these contributions must be added to give the total dose to the target D(r k ) =  D(r k <- r h )

The Residence Time

Residence time is the ratio of cumulative activity to initial activity (in effect how long the radionuclide stays active in the source organ) The ratio t in a source organ t = Ã h / A 0 = F x t 1/2 / ln(2) where A 0 is the administered activity at zero time , F is the fraction of administered activity that arrives in the source organ and t 1/2 is the effective half life

Worked Example

• Male adult, 400 MBq of Tc99m for bone marrow imaging • Fractional uptake of 65% in the liver, 15% in spleen and 20% in red marrow • Uptake is immediate, and there is no biological elimination • Activity in all other tissues is negligible

Worked Example

• Residence time of each organ: – As there is no biological elimination, effective half life = physical half life – Tc99m = 6.02 h = 21,672 s – t liver = 0.65 x 21,672/ln(2) = 20 x 10 – t spleen 3 s = 0.15 x 21,672/ln(2) = 4.69 x 10 3 – t marrow = 0.20 x 21,672/ln(2) = 6.25 x 10 3 s s

Worked example

• Absorbed Dose (per MBq) in each target organ: – For a particular target organ, need to multiply source organ residence time by S value for each source organ and add them together to give absorbed dose from its exposure to that source organ – Let’s concentrate on absorbed dose to the bladder: – S values of source organs: • Liver: 1.16 x 10 -8 mGy/MBq/s • Spleen: 0.08 x 10 -8 mGy/MBq/s • Red marrow: 9.16 x 10 -8 mGy/MBq/s – So absorbed dose (per MBq) to the bladder: • (1.16 x 10 -8 x 20 x 10 3 ) + (0.08 x 10 -8 x 4.69 x 10 3 ) + (9.16 x 10 -8 6.25 x 10 3 ) =

0.85 x 10 -3 mGy/MBq

– This is repeated for all target organs in the body x

Worked Example

• We then calculate the equivalent dose to each target organ – Multiply absorbed dose by radiation weighting factor W r – For radiations emitted by Tc99m (gamma), W r = 1 – So absorbed dose is numerically equal to equivalent dose

Worked Example

• We now need to calculate the effective dose – Multiply the equivalent dose by the tissue weighting factor W t – For the bladder, W t = 0.04

– So we get: • • 0.85 x 10 -3 x 0.04 =

3.4 x 10 JUST FOR THE BLADDER -5 mSv/MBq

–

WE NEED TO REPEAT THIS FOR EACH TARGET ORGAN

– –

ADD THEM ALL TOGETHER THIS GIVES US THE EFFECTIVE DOSE

Effective Dose = 4.1 mSv

ICRP ICRP publications 53, 62 & 80 give the absorbed dose per unit activity administered (mGy/MBq) for different radiopharmaceuticals and different organs as well as the effective dose.

Typical Effective Doses for Cardiac Imaging Radionuclide Investigation Tc99m DRL (MBq) Effective Dose (mSv) 10 Uterine Dose (mGy) 6 Tc99m (Human Albumin) Tc99m (normal erythrocytes) First pass blood flow imaging 800 Cardiac blood pool imaging 800 Cardiac blood pool imaging 800 5 6 4 3 Tc99m (sestamibi) Myocardial imaging 300 800 (SPECT) Tc99m (tetrofosmin) Tl201 Myocardial imaging 300 800 (SPECT) Myocardial imaging 80 3 8 2 6 14 2 6 2 6 4 Tl201 Myocardial imaging (re-injection technique) 120 21 6

•

Assumptions in Standard MIRD Dosimetry

Entire organs taken as sources and targets • Homogeneous absorbing material • Uniform activity distribution • Constant mass • Edge effects are negligible

Other radiation exposure/dose metrics

• Air kerma (Gy) - energy released in 1 kg of air

(dose meters usually read in air kerma)

• Dose equivalent (Sv) - superseded by equivalent dose in 1990 (

slightly different values of w R for neutrons)

• Effective dose equivalent (Sv) - superseded by effective dose in 1990 (

slightly different values of w T )

• Ambient dose equivalent (Sv) - dose a particular depth

(often used for personal dosimeter results, e.g. H p,10 is dose at 10 mm deep in tissue)

• Committed effective dose (Sv) – from ingested radionuclides over 50 y .

Take home message:

If in doubt ask a physicist

Back to the radiation effects

Two Types of Radiation Effect

•Tissue reactions

•

deterministic effects/ non-stochastic effects

•Stochastic effect (“chance effects”) •

somatic

(effects the exposed individual)

•

hereditary

(effects the progeny of the exposed individual)

Deterministic Effects (tissue reactions)

• 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

6000 5000 Threshold levels of absorbed dose 5000 (minimum for 1% incidence) 4000 3500 3000 3000 2500 2000 2000 1000 500 500 500 150 50 0

From FDA, Sept 1994, “Avoidance of serious x-ray induced skin injuries to patients during fluoroscopically guided procedures” Effect Early transient erythema Temporary epilation Main erythema Permanent epilation Dry desquamation Invasive fibrosis Dermal atrophy Telangiectasis Moist desquamation Late erythema Dermal necrosis Secondary ulseration Threshold Dose 2 Gy 3 Gy 6 Gy 7 Gy 10 Gy 10 Gy 11 Gy 12 Gy 15 Gy 15 Gy 18 Gy 20 Gy Fluoroscopy time to reach threshold Typical fluoro. dose rate of 20 mGy/min 1 hr 42 min 2½ hr 5 hr 6 hr 8 hr 8 hr 9 hr 10 hr 12½ hr 12½ hr 15 hr 17 hr High-level dose rate of 200 Gy/min 10 min 15 min 30 min 35 min 50 min 50 min 55 min 1 hr 1 hr 15 min 1 hr 15 min 1 hr 30 min 1 hr 40 min Time to onset of effect hours 3 weeks 10 days 3 weeks 4 weeks > 14 wks > 52 wks 4 weeks 6-10 wks > 10 wks > 6 wks The higher the dose above the threshold, the worse the injury

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

Fig. A

6-8 weeks after multiple coronary angiography and angioplasty procedures

Fig. B

16 to 21 weeks after procedure, with small ulcerated area present

Fig. C

18-21 months after procedure, evidencing tissue necrosis

Fig. D

Close up of lession in Fig. C From injury, dose probably in excess of 20 Gy

Fig. E

Appearance after skin grafting procedure

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)

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

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

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

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

To prevent deterministic effects

• Keep skin dose below 2 Gy • Keep eye dose below 500 mGy

2011

draft

ICRP recommendations Early and late effects of radiation in normal 16 tissues and organs: threshold doses for tissue reactions and other non-cancer effects of 18 radiation in a radiation protection context • Mostly no significant change to previous threshold doses, but • Some evidence for a threshold acute dose of about

0.5 Gy

(or 500 mSv) to the

heart

and cerebrovascular system for both cardiovascular disease and cerebrovascular disease (1% incidence) • For

cataracts

in the eye lens induced by acute exposures, recent long term studies, indicate threshold around

0.5 Gy

(

previously 5 Gy

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?.

Evidence for stochastic effect

2 Atomic bombs dropped 1945

6 th Aug Hiroshima: 90,000 –166,000 died in 4 months from acute affects 9 th Aug Nagasaki: 60,000 –80,000 died in 4 months from acute affects 15-20% of acute deaths from radiation sickness (i.e. deterministic effects)

Radiation Effects

•

Life Span Study

• Followed 94,000 bomb survivors and 27,000 unexposed people from Hiroshima & Nagasaki from 1950 to present. • • 42% still alive on 1/1/2004 • • By 1998 about 8,000 cancer deaths  940 of these attributable to radiation

(Note – a radiation induced cancer is indistinguishable from a “natural” cancer)

• 21 out of 800 in utero with dose > 10 mSv severely mentally retarded individuals have been identified • No increase in hereditary disease seen http://www.rerf.or.jp/eigo/glossary/lsspopul.htm

Atomic Bomb Survivors 1990

(45 years after exposure) 49,000 430 7570 Still alive in 1990 Non-cancer death "Natural" cancer death Radiation induced cancer death 30,000

Atom Bomb Survivors (LSS) results & ICRP recommended risk factor 0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0 0 ←1 in 20 risk - - - - - - - - - - - → 0.2

↑ 1 Sv mSv) 0.4

0.6

0.8

Dose received / Sieverts

(=1000 1.2

1.4

LSS ICRP60

Linear Non-Threshold

(LNT)

model

ICRP risk factors

(International Commission on Radiological Protection, ICRP Publication 103, 2007)

ICRP definition of "detriment"

The total harm to health experienced by an exposed group and its descendants as a result of the group’s exposure to a radiation source. Detriment is a multidimensional concept. Its principal components are the stochastic quantities: – probability of attributable fatal cancer, – weighted probability of attributable non-fatal cancer, – weighted probability of severe heritable effects, and – length of life lost if the harm occurs.

ICRP Publication 103 (2007) risk factors P(n  1) = 1 - e -(E x risk factor) If E x risk << 1 then P(n  1)  E x risk 5.6 x 10 -5 per mSv  1 in 18,000 detriment (Previous ICRP60 gave risk of fatal cancer 5.0 x 10 -5 per mSv  1 in 20,000 chance)

Risk of fatal cancer from 1 mSv

1 in 20,000 risk

 Risk of fatal car accident in UK in 1 year

Hereditary Effects

• Observed in animal experiments • Not observed in A-bomb victims • ICRP 103 Detriment for severe hereditary disease = 0.2 x 10 -5 per mSv

(i.e. 2 in a million chance per mSv, < 3% of total detriment).

Probability of fatal cancer

(Atom bomb “survivors”) 50 40 30 20 Risk per million per mGy 10 0 0 10 20 30 40 50 60 70 80

Age

• i.e. children risk  3 x adult risk 90

300 200 100 0 0 500

For coronary angiography examinations

Risk by age for coronary angio

male female 400 10 20 30 40 50

Age at exposure

60 70 80 90 100

lung and oesophageal risk and age

http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1317131197532

Pregnancy - Radiation Risks

Age (weeks)

0-1 2-5 5-7 7-21

Lethality

No threshold at day 1?

100 thereafter 250-500 500 > 500 To term > 1000

Minimal dose (mGy) for: Gross malformation Mental retardation

No threshold at day 1?

200 No effects observed to about 8 weeks 500 Very few observed Very few observed Weeks 8-15: no threshold?

Weeks 16-25: threshold dose 600-700 Gy Weeks 25-term: no effects observed

Total risk of cancer up to age 15 years following in utero exposure ( per mGy )

Cancer type Leukaemia Other Total Fatal 1.25  10 -5 1.75  10 -5 3.0  10 -5 Non-fatal 1.25  10 -5 1.75  10 -5 3.0  10 -5 Total 2.5  10 -5 3.5  10 -5 6.0  10 -5 =

1 in 17,000

 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 Fatal cancer to age 15 years Lifetime cancer risk 1  10 -2 to 6  10 -2 7.7  10 -4 20  10 -2 to 25  10 -2 = 170 to 1020 in 17,000 = 13 in 17,000 = 3400 to 4200 in 17,000

For diagnostic procedures

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

Useful References

•HPA 2009 “Protection of Pregnant Patients During Diagnostic Medical Exposures to Ionising Radiation” http://www.hpa.org.uk/webc/HPAwebFile/HPAweb_C/1238230848746 •BIR 2009 “Pregnancy and Work in Diagnostic Imaging Departments” http://www.rcr.ac.uk/docs/radiology/pdf/Pregnancy_Work_Diagnostic_Imaging_2nd.pdf

“Small” individual risks, but big numbers

• 473,715 procedures giving 2,700 mSv • so, about 5.7mSv per procedure • if 1 in 20,000 risk of fatal cancer per millisievert • so 1 in 3,500 risk of fatal cancer to 470,000 people •

– All exposures must be

JUSTIFIED

– Doses to patients, and staff, must be

easonably

chievable (

ALARA principle

)

Justification

• Every medical exposure must be clinically justified by a qualified practitioner – In NM this is always the ARSAC certificate holder, and is called the ‘IRMER Practitioner’ • Sufficient information must be provided by the referring clinician (the ‘IRMER Referrer’) • Expected clinical benefit associated with each type of procedure should have been demonstrated to be sufficient to offset the radiation detriment – Will the exposure to ionising radiation influence the subsequent patient management?

• Part of the justification process is to consider whether there are alternative methods which either do not give radiation exposure to the patient, or lower dose.

Optimisation

• All doses must be as low as reasonably achievable (ALARA) • It is necessary to consider whether it is clinically acceptable to use an alternative radiopharmaceutical which results in reduced dose • And whether the administered activity is ALARP (as low as reasonably practicable) • Optimisation depends on: – the systems available (e.g. single or multi headed gamma camera) and, – the type of data required (e.g. dynamic studies, SPECT etc)

Optimisation

• ARSAC have recommended Diagnostic Reference Levels (DRLs) for standard procedures

Optimisation

• However, clinical conditions may justify an increase (or decrease!) in these activities on an individual basis – Obese patients – Extreme pain and cannot keep still • ARSAC certificate holder must justify!!!

• Doses to other organs should be minimised if possible – Thyroid blocking agents when using radio-iodine-labelled compounds – Encouraging the patient to drink plenty of fluids and to empty their bladder frequently after the procedure to haste excretion

Optimisation – Staff Safety

Internal

Ingested and/or inhaled radionuclides

External

Vials, syringes, patients.

Exposure of the worker

Unpacking radioactive material Activity measurements Storage of sources Internal transports of sources Preparation of radiopharmaceuticals Administration Examination of the patient Care of the radioactive patient Handling of radioactive waste Accidents

Dose to Workers from Patients

Contamination of the worker

•spills •improper administration •emergency surgery of a therapy patient •autopsy of a therapy patient

Contamination

The activity on the hands after elution, preparation and administration of Tc99m-radiopharmaceuticals has been measured to 0.02-200 kBq, which results in a skin dose of 0.005 to 50 mSv/h

Radionuclide

Co-57 Ga-67 Tc-99m In-111 I-123 I-125 I-131 Tl-201

Dose rate mSv*cm2/MBq*h

78 324 243 376 365 417 1694 343

Radiation Protection Measures

•

Time

•

Distance

•

Shielding

•

Prevention of contamination

the time exposed Dose = Dose-rate x Time

Consequence

• Reduce time in contact with radiation sources as much as compatible with the task • Training of a particular task using non radioactive dummy sources helps

Distance

Inverse square law (ISL): Dose-rate



1/(distance) 2 distance

Patient with iodine-131

0.5 0.1 0.06 0.03 mSv/h 1000 MBq I-131 0 0.5 1 2 m

Consequence

• Distance is very efficient for radiation protection • Examples: – long tweezers for handling of sources – big rooms for imaging equipment

incident radiation

Shielding

Barrier thickness transmitted radiation

Shielding

Bench top shield Vial shields Syringe shields

SHIELDING OF SOURCES

Factors affecting the design: •radionuclide •activity •shielding material

PERSONAL PROTECTIVE EQUIPMENT - PPE

•appropriate personal protective equipment be maintained for use in the event of intervention; and •the use of personal protective equipment is considered for any given task, account be taken of any additional exposure that could result owing to the additional time or inconvenience, and of any additional non-radiological risks that might be associated with performing the task while using protective equipment. ”

PROTECTIVE CLOTHING

Appropriate clothing should as a minimum include lab coat and gloves.

Safety equipment needed depends on the type of work

Example unpacking: •check for damage •check for contamination •check the content •check the activity Safety equipment: •protective clothing •contamination monitor •shields •forceps, tongs

SAFETY EQUIPMENT

PREPARATION OF RADIOPHARMACEUTICALS •Shields •Protective clothing •Tools for remote handling of radioactive material •Containers for radioactive waste •Contamination monitor •Decontamination kit •Signs, labels and records

ADMINISTRATION

Syringe shield Gloves Lead apron?

Absorbing pads

Syringe shield

No shield Shielded (2mm W)

0.4 mSv/h 0.004 mSv/h 0.8 mSv/h 4.2 mSv/h 22 mSv/h 0.01 mSv/h 0.04 mSv/h 0.16 mSv/h 400 MBq Tc-99m in 1 ml

Vial Shield

Tc-99m 10 GBq 10 ml 560 mGy/h 1 mGy/h 2 mm lead

Time to receive …

1 GBq Tc-99m gives 17 uSv/h @ 1 metre

• Annual finger dose constraint 150mGy • @ 1 m = 1 year • @ 10 cm = 3.6 days • @ 1 cm = 53 minutes • Annual effective dose constraint 6 mSv • • • @ 1 m = 15 days

@ 10 cm = 3.5 hours @ 1 cm = 2.1 minutes

Do we need lead aprons in NM?

• 141 keV Tc-99m gamma rays – 1 mm Pb = 10% transmission • 364 keV I-131 gamma rays – 11 mm Pb = 10% transmission • 511 keV F-18 gamma rays – 13.5 mm Pb = 10% transmission

CONTAMINATION

To minimize contamination risks

- adopt clean operating conditions - adopt good laboratory practices do not eat, smoke etc… - use protective gloves and clothing

DECONTAMINATION PROCEDURES

• Use adsorbent paper on wet spill or wet absorbent paper on dry spill • Repetitively swab the area inwards towards the center of the spill • Place contaminated paper in a plastic bag or container • Monitor the area • Repeat the procedure until the exposure rate is below given limits • If the decontamination is not successful, mark the contaminated area and classify the room as a controlled area If not already done) until the contamination is completely removed.

Decontamination

120

Remaining activity (%)

100 80 60 40 20 0

Tc99m pertechnetate

0 1 2 3 4

Number of washings

5 6

Decontamination of skin

If contamination of the skin occurs, immediately the area should be thoroughly washed using mild soap and tepid (not hot) water. Particular care should be paid to cleaning under the fingernails. If this does not bring the contamination to an acceptably low level the procedure should be repeated using a decontaminating detergent. Scrub with a nail brush but take care not to break the skin.

DECONTAMINATION OF SKIN

Substance Pertechnetate Tc99m-colloid Remaining activity (%) 1 5 <1 2 Method 7 <1 3 4 -------------------------------------------------------------------------- Tc99m-DTPA 1 0 1 1 Tc99m-MDP 7 1 3 5 5 7 <1 <1 I131-hippuran I131-iodide Ga67-citrate <1 8 3 <1 5 1 <1 <1 <1 4 2 1 In111-DTPA <1 <1 <1 <1 ----------------------------------------------------------------------------

: 90 s in water,

: 90 s in soap and water,

: skin lotion and 90 s in soap and water,

: commercial decontamination substance

Internal Hazard

• Technetium-99m • 6 hour half life • 0.017mSv/h @1m from 1GBq • • ALI = 690 MBq

(Annual Limit of Intake is activity to give you 6 mSv if inhaled or ingested)

• Iodine-131 • 8 day half life • 0.057mSv/h @1m from 1GBq • ALI = 1.8 MBq

Basic Principles

• Any exposure must be justified – JUSTIFICATION • All exposures must be As Low As Reasonably Achievable (ALARA) – OPTIMISATION • Dose limits must never be exceeded

–

LIMITATION

External Hazard

• Minimise time exposed • Maximise distance from sources – Syringes – Vials – Patients – Use handling devises • Use available shielding – Lead shields – Lead glass/acrylic – Syringe shield – Lead pots

Internal Hazards

• Remember that anything contaminated can then contaminate everything that it touches.

• Monitor – when leaving a controlled area – Regularly all areas which may become contaminated