Risks and hazards of ionizing radiation

Endre Szabó

Doses

• Absorbed dose: D=E/m (Joule/kg=gray=Gy)

• Effective dose: Heff= ΣHi * wi (Sievert=Sv)

– gonads – 0.20

– bone marrow, colon,lung, stomach – 0.12

– bladder, oesophagus, breast, thyroid, liver – 0.05

• DAP – dose area product,

• DLP – dose length product, CTDI CT dose index

Ways of cellular damage

• ionization in the chromosomes – direct damage in DNA

• ionization in the cytoplasm – free radicals causing indirect damage of proteins, RNA and DNA

Somatic radiation injury

• Diagnostic range

– threshold dose – deterministic

– stochastic – probability

– summation

– risk of malignancies – latency period

–ocular lens, thyroid gland

• Therapeutic range

– side effects, complications

• Nuclear accident

– acute/chronic radiation disease

Genetic radiation injury

• Manifests in descendants only

• No threshold dose – single photon!!!

• Possible outcomes: – ovum or sperm cell perishes

– ovum or sperm cell is not able to (be) fertilize(d)‏

– embedment is prevented

– abortion

– congenital malformation (dominant)‏

– malformation manifesting in later generations (recessive)‏

Facts&figures:

• Natural Deff=2.4 mSv/y (2/3 is internal)

• 3-4 x 1021 natural radioactive atoms in the body

• Potassium (40K)

• 8500 radioactive decay ≈ 190 µSv/y

• External radiation: 40% cosmic, 60% from Earth

Facts&figures:

• eating a banana – 0.1 µSv

• sleeping (not alone) – 0.5 µSv

• mammography – 3 mSv

• CT chest – 6-23 mSv

• background ≈ 0.1 µSv/h

• population limit – 1 mSv/y

• workers – 20 mSv/y (100 mSv/5y)

Radiation protection:

• indication !!! • pregnancy, 2-20 weeks – beware!

• young women in weeks after ovulation – beware!?

• technical protection – dose reduction

– lead covers

– scattered radiation filtering

– proper collimation

8/40

Risks of radiology

• radiation

• overuse (when? what? why?)

• false results (question? false –ve/+ve)

• unjustified reassurance (CXR vs CT)

Legal background

• EU Euratom 1996, 2012

• ICRP

– Justification – benefit

– Optimisation – ALARA

– Limitation – DRL (Diagnostic Reference Levels)

Do we really need this examination?

Do we really need this now?

Has it been performed recently?

Did I describe the problem well?

Is this the optimal test?

Study Effective dose (mSv) = CXR Background

Extremity 0,01 0,5 1,5 days

CXR 0,02 1 3 days

Skull 0,1 5 2 weeks

L spine 2,4 120 14 months

Hip 0,3 15 2 months

Pelvis 1,0 50 6 months

Abdomen 1,5 75 9 months

Ba-swallow 2,0 100 1 year

Stomach 5,0 250 2,5 years

Enterography 6,0 300 3 years

Ba enema 9,0 450 4,5 years

Urography 4,6 230 2,5 years

Skull CT 2,0 100 1 year

Thorax/abdo CT 8,0 400 4 years

Lung scintigraphy 1,0 50 6 months

Bone scintigraphy 5,0 250 2-5 years

Frequency and cumulative dose of some of the imaging studies

in the UK, 1995

frequency

dose

CT

L spine

Ba enema

GI

IVU

abdomen

pelvis

CXR

extremities

skull

spine

DENTAL

percent

Fetal dose

Examination Doseeff to mother (mSv)

Absorbed dose by fetus

CXR 0.02 <0.001

Abdominal AP 0.45 1

CT head 2 <0.001

CT chest 6 0.02

CT abdomen 10 20

Contrast materials

15/40

Absorption of x-ray is influenced by:

• atomic number4

• wavelength of radiation3

• density • thickness

Z ρ (g/cm3)

N2 7 0.0012

O2 8 0.0014

Air 7.2 0.0013

CO2 7.3 0.0019

I 53 4.9

Ba 56 3.5

soft tissue 7.4 ~ 1

bone ~ 10 ~ 1.5

Pb 82 11.3

Ca 20 1.5

• double contrast Ba swallow, stomach, enterography, enema

• hysterosalpingography

• myelography

• fistulography

• cholangiography (percutaneous or through Kehr-line)‏

• urography

• pneumocystography

• galactography

• pneumo-encephalography

• ventriculo-cysternography

• dacrio-cysternography

• pneumomediastinum, -(retro)peritoneum

• bronchography

• arthrography

• iv. or per os cholangiography

• deferentography

• cavernosography

X-ray/CT contrast materials

negative positive ‏

gas (x-ray, CT) barium iodine water (CT)

water-soluble fat soluble

gastrointestinal intravascular

hydrophilic lipophilic

ionic non- ionic

monomeric dimeric monomeric dimeric

X-ray/CT contrast materials

• bismuth 1896 • barium 1904 • gas - oxygen 1905 - air 1918 • iodinated poppy-seed oil 1921 • tetrabromophenolphtalein 1923 • strontium-bromide 1923 • sodium-iodide 1924 • biiodinated organic molecules 1928 • thorium-dioxide 1931 • triiodinated organic molecules 1950 • non-ionic triiodinated molecules 1985

Barium

Complication:

perforation: foreign body reaction

sterile inflammation

superinfection

aspiration: bronchitis

21/40

Iodine containing i.v. contrast materials

side effects • heat, pain, diuresis complications (minor, severe)‏ • allergic urticaria, Quincke-oedema, anaphylactic shock

• osmotic thrombophlebitis, vasculitis

• chemotoxic thyreotoxic crisis, bronchial spasm, arrhytmia, convulsion, heart arrest

• vasovagal nausea, vomiting, hypotension

22/40

Iodine containing i.v. contrast materials

Prevention of complications

• proper hydration • allergy in history - premedication • reaction in history - other CM • poor condition - non-ionic dimer • renal impairment - dialysis • insufficiency - dialysis already

Iodine containing i.v. contrast materials

Therapy of complications

• secure vein • management of symptoms • fluid administration • antiemetics • antihistamins • oxygen • bronchospasmolytics • steroids • epinephrine • reanimation/ALS

• stop drug

• maintain venous access

• 100% O2 + maintain airway

• lay patient flat with legs elevated

• get help

Primary management

MR contrast materials

• Paramagnetic: gadolinium

T1 signal increase

iv. administration

• Superparamagnetic (ferromagnetic): iron-oxid

T2 signal decrease

iv. or GI administration

• Organ-specific CM

• NSF – kidney function 26/40

US contrast materials

– non transpulmonary

– transpulmonary

– galactose based

– albumin based

– surface bound

– microbubble

gas bubbles high echogenicity

heart and vessels, vascularity, perfusion