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A deterministic effect - exposure of the skin to high doses of ionizing radiation leads to accumulation of lymphocytes in the layers of the skin caused by the effects of cell death and eventually to the development of erythematous skin changes

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Chernobyl, the nuclear power plant disaster that occurred in Ukraine in 1986, is one of the most well known examples of the effects of acute radiation syndrome. Many citizens of Ukraine exhibited characteristics of all three syndromes. Many people are still suffering the effects of this disaster and, to this day, many objects within the area are still contaminated with radioactivity.

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Dose

Primary source of background radiation is from radon

Radon is a naturally occurring gas in the atmosphere that can be trapped in homes

Often leads to lung cancer

Primary source of occupational dose to technologists is from scatter that is emitted from the patient

Best practice to reduce occupational dose is with time, distance, and shielding

Time: limiting the amount of time the radiographer is in the immediate vicinity of a live x-ray beam

Distance: maximizing the distance between the radiographer and x-ray beam whenever possible

Shielding: wear protective lead shielding when working within the vicinity of a live x-ray beam

Radiosensitivity

Deterministic effects have a proportional relationship with radiation; as dose increases, so do the severity of effects

Example: erythema

Stochastic effects are an all or nothing principle; as dose increases the probability that an effect will occur increases, however, the severity of the effect is unchanged

Example: cancer, you either get cancer or you don't

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https://www.nrc.gov/docs/ML1117/ML111711087.pdf

https://radiopaedia.org/articles/linear-energy-transfer?lang=us

https://radiopaedia.org/articles/acute-radiation-syndrome?lang=us#:~:text=In%20the%20hematopoietic%20syndrome%2C%20white,predisposes%20to%20bleeding%20and%20perforation.

https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/09.pdf

https://documents.manchester.ac.uk/display.aspx?DocID=26898#:~:text=Short%2Dterm%20somatic%20effects%20are,%2C%20i.e.%2C%20months%2Fyears.

https://radiopaedia.org/articles/radiation-induced-carcinogenesis?lang=us

https://ncrponline.org/wp-content/themes/ncrp/PDFs/Statement13.pdf

https://pubs.rsna.org/doi/10.1148/90.2.209

https://pubmed.ncbi.nlm.nih.gov/9525414/

https://pubmed.ncbi.nlm.nih.gov/11519304/#:~:text=The%20developing%20embryo%20and%20fetus,congenital%20malformations%20and%20mental%20retardation.

https://www.radiologyinfo.org/en/info/safety-xray

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Developing fetuses and embryo are extremely radiosensitive

Radiation to either can potentially cause:

growth impairment

prenatal or neonatal death

congenital malformations

intellectual disabilities

A dose of 0.1 Gy to the embryo and fetus is recommended as a threshold dose

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Four stages of ARS:

Prodromal period/syndrome:

Acute clinical symptoms within hours of exposure

Can last a few hours to days

Severity of symptoms depends on dose received

Latent Period:

Apparent well being after initial sickness of prodromal period

Can last hours to weeks

No signs of radiation sickness

Precursor to next phase

Manifest Illness:

Reappearance of symptoms

Symptoms include apathy, confusion, decreased number of WBC, RBC, and platelets, dehydration, epilation, exhaustion, diarrhea, fever, headache, infection, hemorrhage, cardiovascular collapse

Severity of symptoms depend on dose received

Recovery or Death

the exposed person(s) either begin to recover or decline until death

Hemopoietic Syndrome:

1-10 Gy whole body dose

Mild prodromal period (begins within hours and can last several days)

Latent period can last four weeks

General feeling of well being

Blood count drops

Manifest illness symptoms include vomiting, mild diarrhea, malaise, lethargy, and fever

Non-lethal dose, recovery begins within 2-4 weeks with full recovery in 6 months

Gastrointestinal (GI) Syndrome:

6-10 whole body dose

Prodromal period starts within hours, lasts up to 1 day; symptoms include vomiting and diarrhea

Latent period can last 3-5 days

Manifest illness is characterized by second wave of nausea and vomiting, diarrhea, loss of appetite, lethargy, fever, GI bleeding; diarrhea then worsens from loose to watery to bloody as symptoms progress

Death within 3-10 days post exposure

Radiation kills intestinal stem cells faster than they are able to renew

Central Nervous System (CNS) Syndrome:

50 Gy or more

Prodromal occurs within minutes with severe nausea and vomiting, nervousness, confusion, burning sensation on skin, loss of vision, loss of consciousness within an hour

Latent period can last up to 12 hours

Symptoms return with greater severity during manifest illness; additional symptoms include disorientation, loss of muscle coordination, difficulty breathing, seizures, loss of equilibrium, ataxia, lethargy, coma

Death occurs within hours to 3 days

No amount of medical intervention will save the exposed victim

Inflammation of cerebral blood vessels leads to fluid leakage into brain causing increased intracranial pressure and/or meningitis

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Short-term VS Long-term Effects

Short-term:  Expected effects after high acute radiation exposure

Effects are typically seen at the cellular level

Can either kill or damage the cell

Damage to the chromosomes of the cell can impair or destroy the cell's reproductive ability

Long-term: Damage to cells that are continually reproducing

Continually reproducing cells are the most sensitive to radiation because any changes made in the parent cell's chromosome structure will be transmitted to its daughters (Law of Bergonie and Tribondeau)

Result is an increasing number of cells that have no beneficial function to the body, yet are absorbing body nutrition at an increasing rate

Example: cancer and cataracts

Acute VS Chronic Effects

Acute: an exposure that is delivered in a short period of time (ex: within a day)

Chronic: an exposure that continues over long periods of time (ex: months or years)

Carcinogenesis: the initiation of cancer formation; a stochastic effect of ionizing radiation with a linear, non-threshold response.

Organ & Tissue Response

The Law of Bergonie & Tribondeau: a theory proposed in 1906 stating that cell/tissue radiosensitivity is dependent on four characteristics

1. Age: younger cells are more radiosensitive than older ones

2. Differentiation: simple cells without specific functions are more sensitive than complex, high functioning cells

3. Metabolic rate: cells that use energy more rapidly are more sensitive

4. Mitotic rate: cells that divide and multiply rapidly are more sensitive

Example: Lymphocytes are very radiosensitive because they are young cells, have simple functions, use more energy and regenerate quickly; neurons, however, are highly radioresistant because they are older cells, have high complex functions, have lower metabolic rates, and do not reproduce

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absorbed dose: the measure of energy that is deposited into a medium by ionizing radiation

Unit of measure is the Gray (Gy)

dose equivalent: the absorbed dose of tissue multiplied by its radiation weighting factor

Expressed as EqD = D x WR

where D = absorbed dose

Unit of measure is the Sievert (Sv)

exposure: the amount of ionizing radiation in air

Unit of measure is Coulombs/kilogram

effective dose: the sum of the weighted equivalent doses for all irradiated tissues or organs.

Expressed as EfD = D x (WR) x (WT)

where D = absorbed dose

Unit of measure is the Sievert (Sv)

air kerma: the concentration of radiation exposure at the surface of the body

Acronym: Kinetic Energy Released in Matter

Unit of measure is (Joules/kilogram)^2 (same as Gray)

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Dose-response Relationships

Non-linear, threshold

there is no bodily response to radiation until a certain dose level is reached

beyond that level, the response becomes more effective until it reaches the inflection point

the inflection point demonstrates at what dose cells/tissues/organs alter their response; this causes the curve to take on a non-linear shape

Non-linear, non-threshold

a bodily response can be elicited at any amount of radiation

the elicited response becomes more effective until the inflection point, the point at which cells/tissues/organs alter their response to the radiation causing the curve to take on a non-linear shape

example: when cells start dying off, the maximum damage is done so the response curve decreases

Linear, threshold

there is no bodily response to radiation until a certain dose level is reached

beyond that level, the response becomes more effective until it reaches the inflection point

as dose increases, biologic response increases

characterized by deterministic effects (health effects, the severity of which varies with the dose and for which a threshold is believed to exist. The severity of these effects, rather than probability, increases with dose)

Linear, non-threshold

a bodily response can be elicited at any amount of radiation

as dose increases, biologic response increases

characterized by stochastic effects (health effects that occur randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose without threshold)

Relative Tissue Radiosensitivities

Linear Energy Transfer (LET): is the average (radiation) energy deposited per unit path length along the track of an

High LET: more likely to produce biological damage in a given volume of tissue due to its direct effect/hits

Does not travel far in tissue

Particulate radiation (alpha particles, low energy neutrons)

Low LET: less likely to produce tissue damage in the same volume of tissue by creating free radicals through indirect effect/hits

Travels far in tissue and is highly penetrating

More damaging in highly oxygenated tissues

EM radiation (x-ray and gamma rays)

Relative Biologic Effectiveness (RBE): the principle that biologic damage increases with increasing LET

Identical doses of both high LET and low LET will not produce the same biologic effect

Cell Survival and Recovery (LD50)

Lethal dose (LD) 50/30 is a whole body dose that is lethal to 50% of the exposed population within 30 days

<3-4 Gy = human survival

>6 Gy = 100% death rate without medical intervention

>10 Gy = 100% death rate no matter what medical intervention

LD 50/60 (whole body dose that is lethal to 50% of the exposed population within 60 days) is considered to be more accurate

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Genetically Significant Dose

a way of comparing and evaluating the genetic impact of various sources of radiation and its effects

It combines the frequency of radiological examinations obtained during the country-wide survey and estimates of gonadal doses for different examination types, together with population and child expectancy data

Gonadal Shielding

The National Council on Radiation Protection (NCRP) has concluded that in most circumstances gonadal shielding use does not contribute significantly to reducing risks from exposure and may have the unintended consequences of increased exposure and loss of valuable diagnostic information, and therefore is not justified as a routine part of radiological protection. The NCRP now recommends that gonadal shielding not be used routinely during abdominal and pelvic radiography, and that federal, state, and local regulations and guidance should be revised to remove any actual or implied requirement for routine gonadal shielding.