Early Effects Of Radiation Flashcards by Gracie Costello

What are the classifications of biological effects due to ionizing radiation?

Somatic

Genetic (hereditary)

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Biological effects that appear in the exposed person
Two classifications:
-early - appear right away
-late - appear later in life

Somatic effects

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Biological effects that appear in future generations as a result of radiation damage to reproductive cells

Genetic (hereditary) effects

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T/F
Risks for genetic effects in humans are seen to be considerably smaller than the risks for somatic effects

True

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The science that deals with the incidence, distribution and control of disease in a population
-studies consist of observations and statistical analysis of data

Epidemiology

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Why are the studies of epidemiology important?

To make dose response estimates to predict the risk at low doses

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Somatic effects are effects that are cell-killing and directly related to the dose received
-have a dose threshold
-an increase in dose increases the severity

Deterministic
*non-stochastic

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What are some examples of deterministic (non stochastic) effects?

-radiation burns (erythema)

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Somatic effects that are mutational or randomly occurring biological somatic changes that occur independent of dose
-no dose threshold
-an increase in dose increases the probability, but not the effect or severity

Probabilistic (stochastic)

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What are examples of probabilistic (stochastic) effects?

-cancer
-genetic effects

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Plotted as curves and are a graphical representation between observed effects of radiation and amount of radiation received
-linear or non-linear
-threshold or non-threshold

Dose response relationships

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-a point or level at which a response or reaction to an increasing stimulation first occurs
-as one increases the other increases

Linear threshold dose response (LT DR)

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-curves are sigmoid and are predominantly applied to high dose effects observed in radiation therapy
-usually threshold
-non-linear relationship between dose and effect

Non-linear threshold dose response (NLT DR)

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-radiation absorbed dose of any magnitude has the capability of producing a biologic effect
-no radiation dose is “safe”
-severity of biological effects increase directly with the magnitude of the absorbed dose

Linear non-threshold dose response (LNT DR)

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-no threshold, symptoms can occur at any dose
-non-linear relationship
Ex. Leukemia, breast cancer, other genetic damage

Non-linear non-threshold dose response

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What type of effects are non-threshold?

Probabilistic

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What type of effects are threshold?

Deterministic

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T/F
Diagnostic imaging does not normally impose radiation doses sufficient to cause early tissue reactions

True
*except for some lengthy high dose rate fluoroscopic procedures

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T/F
For early tissue reactions, severity is dose related

True

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-also known as radiation sickness
-in humans, after whole body large doses of ionizing radiation over a short time

Acute radiation syndrome (ARS)
Studies from:
-Hiroshima
-Chernobyl
-radiation therapy patients
-…

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What are the four stages of acute radiation syndrome?
(ARS)

Prodromal
Latent period
Manifest illness
Recovery or death

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-initial stage
-occurs within hours of a whole body absorbed dose of 1Gy or more
-symptoms include nausea, vomiting, diarrhea, fatigue, leukopenia (decrease in white blood cells)
-severity is dose related
-stage can last for hours or days

ARS : prodromal stage

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-approx. 1 week of torment symptoms
-period where recovery or lethal effects begin

ARS : latent period

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-stage where symptoms become evident
-symptoms : dehydration, exhaustion, vomiting, severe diarrhea, infection….. see slide 24

ARS: manifesting illness

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-with doses between *2-3 Gy*, patients may pass through first 3 stages and show less severe symptoms than those exposed to lethal doses of *6-10Gy* -recovery may occur within 3 months -those who recover may show signs of radiation damage and experience late effects

ARS : recovery or death

What are the 3 dose related syndromes that occur as part of the total body syndrome?

-hematopietic -gastrointestinal -cerebrovascular

-also known as bone marrow syndrome -whole body dose of *1-10Gy* -decreased WBC (infection) -decreased RBC (carry oxygen) -decreased platelets

Hematopoietic syndrome

What system is the most radiosensitive vital organ in the human body?

Hematopoietic system

-death may occur in 6-8 weeks, usually due to infection and hemorrhage due to the effect on the blood cells -if radiation exposure is not lethal, bone marrow cells will repopulate

Hematopoietic syndrome

What increases the survival probability of hematopoietic syndrome?

Intensive medical support -bone marrow transplant

-threshold dose of *6-10Gy* -results in death 3-10 days after exposure without medical intervention -repair of epithelial cells is possible, but if regeneration is not accomplished death occurs

Gastrointestinal syndrome -prodromal - few hours after dose -latent - up to 5 days -manifest period follows

What is most affected in gastrointestinal syndrome?

Small intestine

T/F Death usually occurs in 3-5 days with gastrointestinal syndrome due to the catastrophic damage of epithelial cells that line the GI tract

True -hematopoietic syndrome also occurs

-results when the central nervous system and cardiovascular system receive doses of *50 Gy* or more -death occurs within a few hours to 3 days after -prodromal stage after irradiation

Cerebrovascular system

T/F With cerebrovascular syndrome, hematopoietic and gastrointestinal syndrome also occur but death occurs before symptoms are seen

True

Signifies whole body dose that can be lethal to 50% of the exposed population in 30 days

Lethal dose

What is the estimated lethal dose in adults without medical support

3-4 Gy *for xray this is equivalent an equivalent dose of 3-4Sv

Without medical support what is the whole body dose that will cause death to the entire population in 30 days?

6 Gy

T/F With medical support, some humans have survived doses as high as 8.5 Gy

True

Regardless of treatment, what is considered fatal

Over 12 Gy is considered fatal

What does the cells contain that can save and repair a cell and allow it to recover?

Repair enzymes

What occurs to tissue when the recovery after exposure fails?

Necrosis of the structure

What tissue is most radiosensitive? *local tissue damage

Skin, bone marrow

What are the 3 layers of skin?

-epidermis -dermis -hypodermis

What contributes to the relative radio-sensitivity of skin?

High proliferation rate (2% of skin cells are replaced daily by stem cells - this accounts for its sensitivity)

What can be caused due to radiation of the hair follicles which are growing tissue?

Epilation or alopecia

Doses as low as ______ can affect the reproductive system

0.1 Gy (10rad)

What is more radiosensitive, sperm or ova?

Ova

T/F Tested contain both mature and immature spermatogonia

True *constantly reproducing and developing into mature sperm (3-5weeks)

What will result from a reduction in the number of mature sperm?

Maturation depletion

What dose may result in male temporary sterility for as long as 12 months?

Dose of 2 Gy

What dose may result in permanent sterility in males?

Dose of 5-6 Gy *can also result in atrophy

What stages of life are ovaries very radiosensitive because they contain a large number of stem cells (oogonia) and immature cells (oocytes)

Fetal and early childhood stages

After puberty, how many mature ova will be produced?

400-500

For females, what dose may delay or suppress menstruation

0.1 Gy

What age does the radiosensitvity of the ovaries decline?

20-30

T/F Radiosensitivity increases again after approx. 30 years of age because new ova are not replenished after they have been lost

True

For females, what exposure will result in temporary sterility?

2 Gy

For females, what dose will result in permanent sterility?

5-6 Gy *genetic mutation is possible

Doses as low as _____ may cause fertility issues, and chromosomal damage and mutations passed to future generations may occur

0.25 Gy

What whole body dose would produce a measurable hematologist depression causing a decrease in lymphocytes creating a greater chance for infection

As little as 0.25 Gy

T/F Blood counts were once routinely used to determine any degree of occupational radiation exposure

True

What are the most evident hematologic effects of radiation exposure?

Found in the decrease of cells in the peripheral circulation (indicative of effects of rad in bone marrow) -anemia

Mapping of chromosomes

Karyotyping -done during metaphase