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

Radiation Hazards and Dosimetry

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Radiation Hazards and Dosimetry. Dr. Craig Moore Medical Physicist & Radiation Protection Adviser Radiation Physics Service CHH Oncology. In the beginning. - PowerPoint PPT Presentation

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Page 1: Radiation Hazards and Dosimetry

Radiation Hazards and Dosimetry

Dr. Craig Moore

Medical Physicist & Radiation Protection Adviser

Radiation Physics Service

CHH Oncology

Page 2: Radiation Hazards and Dosimetry

In the beginning ...• Wilhelm Roentgen discovered X-rays

on 8th 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)

Page 3: Radiation Hazards and Dosimetry

First Human Radiograph

• Frau Roentgen’s hand

• Not medical - possibly to show off expensive gold ring??

Page 4: Radiation Hazards and Dosimetry

First US medical radiograph

• 3rd 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.)

Page 5: Radiation Hazards and Dosimetry

X-rays became all the rageAssumed to be no more harmful than light

Dr Rome Wagner & glamorous assistant

Unshielded Glass X-ray

tube

“Fluoroscope” - fluorescent screen inside black card

Page 6: Radiation Hazards and Dosimetry

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

Page 7: Radiation Hazards and Dosimetry

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

Page 8: Radiation Hazards and Dosimetry

Early exampleIn 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.”

Page 9: Radiation Hazards and Dosimetry

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

Page 10: Radiation Hazards and Dosimetry

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”)

Page 11: Radiation Hazards and Dosimetry

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 RollinsAs 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)

Page 12: Radiation Hazards and Dosimetry

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

Page 13: Radiation Hazards and Dosimetry

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 0.001oC– i.e. less heating effect than a sip from a cup of hot tea

• 19th 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.

Page 14: Radiation Hazards and Dosimetry

First Radiotherapy TreatmentEmil Herman Grubbé

• Not all bad news!

• 29th January 1896

• Woman (50) with breast cancer

• 18 daily 1-hour irradiation

• Condition was relieved, although died shortly afterwards from metastases.

Page 15: Radiation Hazards and Dosimetry

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

Aside

Page 16: Radiation Hazards and Dosimetry

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.”

Page 17: Radiation Hazards and Dosimetry

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 20th century

• Whether radiation induced cancer was still a matter of debate

Page 18: Radiation Hazards and Dosimetry

Radiation / Cancer link provenRadiation / Cancer link proven

Page 19: Radiation Hazards and Dosimetry

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

Page 20: Radiation Hazards and Dosimetry

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.

Page 21: Radiation Hazards and Dosimetry

Ionising Radiation

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

+

-

Page 22: Radiation Hazards and Dosimetry
Page 23: Radiation Hazards and Dosimetry

Why is it

dangerous?

Page 24: Radiation Hazards and Dosimetry

X-ray passes straight

through cell

No change to cell

Page 25: Radiation Hazards and Dosimetry

X-ray causes a

chemical reaction in cell, but no damage

done or damage repaired by cell

No change to cell

Page 26: Radiation Hazards and Dosimetry

DNA damaged in a“fatal” way”

Cell killed

Page 27: Radiation Hazards and Dosimetry

DNA damaged,causing cell to

reproduceuncontrollably

Cancer?

Page 28: Radiation Hazards and Dosimetry

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

Page 29: Radiation Hazards and Dosimetry

Quantifying Radiation, to quantifying the risk

Aside:

Page 30: Radiation Hazards and Dosimetry

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”

Page 31: Radiation Hazards and Dosimetry

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 Gy entrance surface dose .

Page 32: Radiation Hazards and Dosimetry

Different radiations, different risk

• Multiplying ABSORBED DOSE in Gy by a weighting factor (wR) for the relative damage cause by different radiations gives us EQUIVALENT DOSE

• 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

Page 33: Radiation Hazards and Dosimetry

Equivalent Dose (HT,R)

• Absorbed dose to tissue x radiation weighting factor

• In mathematical notation– HT,R = wR.DT,R

– or if exposed a mix of radiations HT = R wR.DT,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.

Page 34: Radiation Hazards and Dosimetry

Equivalent Dose (HT,R)

weighting factors, wR• HT,R = wR.DT,R

• wR = 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),

• wR = 5-20 for neutrons, (depending on energy)

• wR = 5 for protons (beginning to be used in radiotherapy),

• wR = 20 for alpha () particles (recently used for palliative nuclear

medicine therapy),

• e.g. for X-rays 1 Gy = 1 Sv, but for alpha particles 1 Gy = 20 Sv .

Page 35: Radiation Hazards and Dosimetry

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 cm2 of skin of radiation workers = 500 mSv equivalent

dose per calendar year

Page 36: Radiation Hazards and Dosimetry

Different organs or tissues, different risk

• 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

• 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

Page 37: Radiation Hazards and Dosimetry

Effective Dose (E)• Sum of equivalent doses to each

tissue/organ x organ weighting factors wT

• E = T wT.HT

• Units are Sieverts (Sv)

• You need to know the dose to each organ/tissue of interest.

Page 38: Radiation Hazards and Dosimetry

• wT = 12% for red bone marrow, breast, colon, lung, stomach,

• wT = 8% for gonads

• wT = 4% for liver, oesophagus, thyroid, bladder

• wT = 1% for skin, bone surfaces, brain, salivary glands

• wT = 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

ICRP Publication 103 (2007) tissue weighting factors

Page 39: Radiation Hazards and Dosimetry

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

Page 40: Radiation Hazards and Dosimetry

Tissue or Organ

Organ dose, HT (mSv)

Weighting Factor, wT HT x wT (mSv)

Ovaries 0.805 0.04 0.032

Testes 0.079 0.04 0.003

Lungs 0.037 0.12 0.004

Stomach 0.417 0.12 0.050

Colon 0.718 0.12 0.086

RBM 0.599 0.12 0.072

Thyroid 0.000 0.04 0.000

Breasts 0.007 0.12 0.001

Oesophagus 0.042 0.04 0.002

Liver 0.518 0.04 0.021

Urinary bladder 0.450 0.04 0.018

Skin 0.386 0.01 0.004

Total bone 0.697 0.01 0.007

Brain 0.000 0.01 0.000

Salivary glands 0.000 0.01 0.000

Average remainder 0.472 0.12 0.057

Effective dose = T wT.HT 0.36 mSv

Page 41: Radiation Hazards and Dosimetry

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.

Page 42: Radiation Hazards and Dosimetry

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

Page 43: Radiation Hazards and Dosimetry

Typical Values of E (X-ray examinations)

• Barium enema = 7 mSv• CT abdomen = 10 mSv• Conventional abdomen = 1.0 mSv• Chest PA = 20 Sv• Pulmonary angiography = 5.4 mSv

• Annual effective dose limit for radiation workers = 20 mSv

• Annual background dose = 2.5 mSv .

Page 44: Radiation Hazards and Dosimetry

How do we apply this to Nuclear Medicine?

Page 45: Radiation Hazards and Dosimetry

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 within the

body and its uptake in certain 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.

Page 46: Radiation Hazards and Dosimetry

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

Page 47: Radiation Hazards and Dosimetry

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 target organ – 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

Page 48: Radiation Hazards and Dosimetry
Page 49: Radiation Hazards and Dosimetry

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

Page 50: Radiation Hazards and Dosimetry

Absorbed Dose

• Energy absorbed in a material per unit mass

• Has unit of the gray (1 Gy = 1 J/kg)

Page 51: Radiation Hazards and Dosimetry

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

Page 52: Radiation Hazards and Dosimetry

Absorbed Fraction

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

Page 53: Radiation Hazards and Dosimetry

Absorbed Fraction

Target Target OrganOrgan

Source OrganSource Organ

• 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

Page 54: Radiation Hazards and Dosimetry

Examples of Absorbed FractionsNote: = 1 for charged particles

Page 55: Radiation Hazards and Dosimetry

Determination of the Absorbed Fraction

The only method available is

CALCULATION

using Monte Carlo modelling

Page 56: Radiation Hazards and Dosimetry

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!!!!!

Page 57: Radiation Hazards and Dosimetry

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

Page 58: Radiation Hazards and Dosimetry

MIRD Pamphlet MIRD Pamphlet No. 5 Revised.No. 5 Revised.

J Nucl MedJ Nucl Med Jan Jan 19781978

The MIRD Standard Man

Page 59: Radiation Hazards and Dosimetry

MIRD Pamphlet MIRD Pamphlet No. 5 Revised.No. 5 Revised.

J Nucl MedJ Nucl Med Jan Jan 19781978

The MIRD Standard

Man

Page 60: Radiation Hazards and Dosimetry

Derivation of the General MIRD Equation

• If A is the activity of the source, the cumulated activity à 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

Page 61: Radiation Hazards and Dosimetry

Derivation of the General MIRD Equation

• ÃnE is the energy absorbed in the target organ during the time interval of interest ( is the absorbed fraction)

• D = ÃnE/m is the absorbed dose in the target organ, where m is the mass of the target organ

Page 62: Radiation Hazards and Dosimetry

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

Page 63: Radiation Hazards and Dosimetry

Derivation of the General MIRD Equation

Generally each radionuclide will emit more than one type of “particle”

D = Ã Si where Si is the S factor of the ith particle

Page 64: Radiation Hazards and Dosimetry

Derivation of the General MIRD Equation

Generally there will be many source organs rh contributing to the target organ rk, and all these contributions must be added to give the total dose to the target organ.

D(rk) = D(rk <- rh)

Page 65: Radiation Hazards and Dosimetry

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 in a source organ

= Ãh / A0 = F x t1/2 / ln(2)

where A0 is the administered activity at zero time, F is the fraction of administered activity that arrives in the source organ and t1/2 is the effective half life

Page 66: Radiation Hazards and Dosimetry

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

Page 67: Radiation Hazards and Dosimetry

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

– tliver = 0.65 x 21,672/ln(2) = 20 x 103 s

– tspleen = 0.15 x 21,672/ln(2) = 4.69 x 103 s

– tmarrow = 0.20 x 21,672/ln(2) = 6.25 x 103 s

Page 68: Radiation Hazards and Dosimetry

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 103) + (0.08 x 10-8 x 4.69 x 103) + (9.16 x 10-8 x

6.25 x 103) = 0.85 x 10-3 mGy/MBq

– This is repeated for all target organs in the body

Page 69: Radiation Hazards and Dosimetry

Worked Example

• We then calculate the equivalent dose to each target organ– Multiply absorbed dose by radiation weighting

factor Wr

– For radiations emitted by Tc99m (gamma), Wr = 1

– So absorbed dose is numerically equal to equivalent dose

Page 70: Radiation Hazards and Dosimetry

Worked Example

• We now need to calculate the effective dose– Multiply the equivalent dose by the tissue weighting

factor Wt

– For the bladder, Wt = 0.04– So we get:

• 0.85 x 10-3 x 0.04 = 3.4 x 10-5 mSv/MBq• JUST FOR THE BLADDER

– WE NEED TO REPEAT THIS FOR EACH TARGET ORGAN

– ADD THEM ALL TOGETHER– THIS GIVES US THE EFFECTIVE DOSE

Page 71: Radiation Hazards and Dosimetry

Effective Dose = 4.1 mSv

Page 72: Radiation Hazards and Dosimetry

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.

Page 73: Radiation Hazards and Dosimetry

Typical Effective Doses for Cardiac ImagingRadionuclide Investigation DRL (MBq) Effective

Dose (mSv)Uterine Dose (mGy)

Tc99m First pass blood flow imaging

800 10 6

Tc99m (Human Albumin)

Cardiac blood pool imaging

800 5 4

Tc99m (normal erythrocytes)

Cardiac blood pool imaging

800 6 3

Tc99m (sestamibi) Myocardial imaging 300

800 (SPECT)

3

8

2

6

Tc99m (tetrofosmin)

Myocardial imaging 300

800 (SPECT)

2

6

2

6

Tl201 Myocardial imaging 80 14 4

Tl201 Myocardial imaging (re-injection technique)

120 21 6

Page 74: Radiation Hazards and Dosimetry

Assumptions in Standard MIRD Dosimetry

• Entire organs taken as sources and targets

• Homogeneous absorbing material

• Uniform activity distribution

• Constant mass

• Edge effects are negligible

Page 75: Radiation Hazards and Dosimetry

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 wR for neutrons)

• Effective dose equivalent (Sv) - superseded by effective dose in 1990 (slightly different values of wT)

• Ambient dose equivalent (Sv) - dose a particular depth (often used for personal dosimeter results, e.g. Hp,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

Page 76: Radiation Hazards and Dosimetry

Back to the radiation effects

Page 77: Radiation Hazards and Dosimetry

•Stochastic effect (“chance effects”)•somatic (effects the exposed individual)

77

Two Types of Radiation Effect

•Tissue reactions •deterministic effects/ non-stochastic effects

• hereditary (effects the progeny of the exposed individual)

Page 78: Radiation Hazards and Dosimetry

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 .

Page 79: Radiation Hazards and Dosimetry

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

Threshold levels of absorbed dose(minimum for 1% incidence)

Page 80: Radiation Hazards and Dosimetry

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

The higher the dose above the threshold, the worse the injury

Page 81: Radiation Hazards and Dosimetry

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 .

Page 82: Radiation Hazards and Dosimetry

Fig. A6-8 weeks after multiple coronary angiography and angioplasty procedures

Page 83: Radiation Hazards and Dosimetry

Fig. B16 to 21 weeks after procedure, with small ulcerated area present

Page 84: Radiation Hazards and Dosimetry

Fig. C18-21 months after procedure, evidencing tissue necrosis

Page 85: Radiation Hazards and Dosimetry

Fig. DClose up of lession in Fig. C

From injury, dose probably in excess of 20 Gy .

Page 86: Radiation Hazards and Dosimetry

Fig. EAppearance after skin grafting procedure .

Page 87: Radiation Hazards and Dosimetry

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)

Page 88: Radiation Hazards and Dosimetry

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

Page 89: Radiation Hazards and Dosimetry

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

Page 90: Radiation Hazards and Dosimetry

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

Page 91: Radiation Hazards and Dosimetry

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

Page 92: Radiation Hazards and Dosimetry

To prevent deterministic effects

• Keep skin dose below 2 Gy

• Keep eye dose below 500 mGy .

Page 93: Radiation Hazards and Dosimetry

2011 draft ICRP recommendationsEarly 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).

Page 94: Radiation Hazards and Dosimetry

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?.

Page 95: Radiation Hazards and Dosimetry

Evidence for stochastic effect

2 Atomic bombs dropped 1945

6th Aug Hiroshima: 90,000–166,000 died in 4 months from acute affects

9th 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)

Page 96: Radiation Hazards and Dosimetry

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.

Page 97: Radiation Hazards and Dosimetry

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

Page 98: Radiation Hazards and Dosimetry

Atomic Bomb Survivors 1990 (45 years after exposure)

49,000 30,000

7570430

Still alive in 1990

Non-cancer death

"Natural" cancer death

Radiation induced cancer death

Page 99: Radiation Hazards and Dosimetry

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

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Dose received / Sieverts

Fata

l can

cer r

isk

LSS

ICRP60

←1 in 20 risk

↑ 1 Sv (=1000

mSv)

- - - - - - - - - - - -→

Linear Non-Threshold (LNT) model

Page 100: Radiation Hazards and Dosimetry

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

Page 101: Radiation Hazards and Dosimetry

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.

Page 102: Radiation Hazards and Dosimetry

ICRP Publication 103 (2007) risk factors

5.6 x 10-5 per mSv 1 in 18,000 detriment

P(n 1) = 1 - e-(E x risk factor)

If E x risk << 1 then P(n 1) E x

risk

(Previous ICRP60 gave risk of fatal cancer5.0 x 10-5 per mSv 1 in 20,000 chance)

Page 103: Radiation Hazards and Dosimetry

1 in 20,000 risk

Risk of fatal cancer from 1

mSv

Risk of fatal car accident in UK in 1

year

Page 104: Radiation Hazards and Dosimetry

• 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).

Hereditary Effects

Page 105: Radiation Hazards and Dosimetry

0

10

20

30

40

50

0 10 20 30 40 50 60 70 80 90

Age

Ris

kProbability of fatal cancer

(Atom bomb “survivors”)

• i.e. children risk 3 x adult risk

Risk per million per mGy

Page 106: Radiation Hazards and Dosimetry

Risk by age for coronary angioFor coronary angiography examinations (HPA-CRCE-028 table 20)

0

100

200

300

400

500

0 10 20 30 40 50 60 70 80 90 100

Age at exposure

Can

cer

risk

per

mil

lio

n

male female

Page 107: Radiation Hazards and Dosimetry

lung and oesophageal risk and age

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

Page 108: Radiation Hazards and Dosimetry

Pregnancy - Radiation RisksAge 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

Page 109: Radiation Hazards and Dosimetry

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

= 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 1 10-2 to 6 10-2 = 170 to 1020 in 17,000

Fatal cancer to age 15 years 7.7 10-4 = 13 in 17,000

Lifetime cancer risk 20 10-2 to 25 10-2 = 3400 to 4200 in 17,000

Page 110: Radiation Hazards and Dosimetry

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

Page 111: Radiation Hazards and Dosimetry

“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

• So– All exposures must be JUSTIFIED– Doses to patients, and staff, must be As Low As

Reasonably Achievable (ALARA principle) .

Page 112: Radiation Hazards and Dosimetry

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.

Page 113: Radiation Hazards and Dosimetry

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)

Page 114: Radiation Hazards and Dosimetry

Optimisation• ARSAC have recommended Diagnostic Reference Levels (DRLs)

for standard procedures

Page 115: Radiation Hazards and Dosimetry

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

Page 116: Radiation Hazards and Dosimetry

Optimisation – Staff Safety

InternalIngested and/or inhaledradionuclides

ExternalVials, syringes, patients.

Page 117: Radiation Hazards and Dosimetry

Unpacking radioactive materialActivity measurementsStorage of sourcesInternal transports of sourcesPreparation of radiopharmaceuticalsAdministrationExamination of the patientCare of the radioactive patientHandling of radioactive wasteAccidents

Exposure of the worker

Page 118: Radiation Hazards and Dosimetry

Dose to Workers from Patients

Page 119: Radiation Hazards and Dosimetry

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

Contamination of the worker

Page 120: Radiation Hazards and Dosimetry

The activity on the hands after elution, preparation andadministration 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 Dose ratemSv*cm2/MBq*h

Co-57 78Ga-67 324Tc-99m 243In-111 376I-123 365I-125 417I-131 1694Tl-201 343

Contamination

Page 121: Radiation Hazards and Dosimetry

Radiation Protection Measures

•Time•Distance•Shielding•Prevention of contamination

Page 122: Radiation Hazards and Dosimetry

TimeDose is proportional to

the time exposed

Dose = Dose-rate x Time

Page 123: Radiation Hazards and Dosimetry

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

Page 124: Radiation Hazards and Dosimetry

Distance

distance

do

se-r

ate Dose-rate 1/(distance)2

Inverse square law (ISL):

Page 125: Radiation Hazards and Dosimetry

Patient with iodine-131

1000 MBqI-131

0 0.5 1 2 m

0.5 0.1 0.06 0.03 mSv/h

Page 126: Radiation Hazards and Dosimetry

Consequence

• Distance is very efficient for radiation protection

• Examples:– long tweezers for handling of sources– big rooms for imaging equipment

Page 127: Radiation Hazards and Dosimetry

Shielding

incident radiation transmitted

radiation

Barrier thickness

Page 128: Radiation Hazards and Dosimetry

Shielding

Bench top shieldVial shieldsSyringe shields

Page 129: Radiation Hazards and Dosimetry

SHIELDING OF SOURCES

Factors affecting the design:

•radionuclide•activity•shielding material

Page 130: Radiation Hazards and Dosimetry

•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. ”

PERSONAL PROTECTIVE EQUIPMENT - PPE

Page 131: Radiation Hazards and Dosimetry

PROTECTIVE CLOTHING

Appropriate clothing should as a minimum includelab coat and gloves.

Page 132: Radiation Hazards and Dosimetry

Safety equipment needed depends on the type of work

Safety equipment:•protective clothing•contamination monitor•shields•forceps, tongs

Example unpacking:•check for damage•check for contamination•check the content•check the activity

Page 133: Radiation Hazards and Dosimetry

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

SAFETY EQUIPMENTPREPARATION OF

RADIOPHARMACEUTICALS

Page 134: Radiation Hazards and Dosimetry

ADMINISTRATION

Syringe shieldGloves

Lead apron?Absorbing pads

Page 135: Radiation Hazards and Dosimetry

Syringe shield

400 MBq Tc-99m in 1 ml

No shield

0.4 mSv/h

0.8 mSv/h

4.2 mSv/h

22 mSv/h

Shielded (2mm W)

0.004 mSv/h

0.01 mSv/h

0.04 mSv/h

0.16 mSv/h

Page 136: Radiation Hazards and Dosimetry

Vial Shield

560 mGy/h

1 mGy/h

Tc-99m10 GBq10 ml

2 mm lead

Page 137: Radiation Hazards and Dosimetry

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.

Page 138: Radiation Hazards and Dosimetry

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

Page 139: Radiation Hazards and Dosimetry

CONTAMINATION

Page 140: Radiation Hazards and Dosimetry

To minimize contamination risks

- adopt clean operating conditions - adopt good laboratory practices

- do not eat, smoke etc… - use protective gloves and clothing

Page 141: Radiation Hazards and Dosimetry

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.

Page 142: Radiation Hazards and Dosimetry

0

20

40

60

80

100

120

0 1 2 3 4 5 6

Remaining activity (%)

Number of washings

Tc99m pertechnetate

Decontamination

Page 143: Radiation Hazards and Dosimetry

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.

Page 144: Radiation Hazards and Dosimetry

DECONTAMINATION OF SKIN

Remaining activity (%) Method

Substance 1 2 3 4---------------------------------------------------------------------------Tc99m-DTPA 1 0 1 1Tc99m-MDP 7 1 3 5Pertechnetate 5 7 5 7Tc99m-colloid <1 <1 <1 <1I131-hippuran <1 <1 <1 <1I131-iodide 8 5 <1 2Ga67-citrate 3 1 4 1In111-DTPA <1 <1 <1 <1----------------------------------------------------------------------------1: 90 s in water, 2: 90 s in soap and water, 3: skin lotionand 90 s in soap and water, 4: commercial decontaminationsubstance

Page 145: Radiation Hazards and Dosimetry

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.

Page 146: Radiation Hazards and Dosimetry

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

Page 147: Radiation Hazards and Dosimetry

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.

Page 148: Radiation Hazards and Dosimetry

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

Page 149: Radiation Hazards and Dosimetry

End of lecture