(3) Radiation Health Physics Early Effects of Radiation

Biological effects that appear within hours, days, or a few weeks after radiation exposure are considered ___ effects of radiation?

early

Biological effects that appear months or years after radiation exposure are considered ___ effects of radiation

late

Early radiation effects are classified as?

Somatic & Deterministic

Most late radiation effects are classified as?

 Stochastic & deterministic 

Do early radiation effects generally have a threshold?

Yes

Acute radiation syndrome, local tissue damage, decreased blood cell counts, and cytogenetic effects are examples of what kind of effects?

Early radiation effects

Radiation dermatitis, cataracts, fetal effects are what kind of effects?

 Late deterministic effects

Carcingoeneiss & genetic effects are what kind of effects

Late stochastic effects

The study of the distribution & cause of disease in the human population is termed?

Epidemiology

Why is epidemiology difficult for studying late radiation effects?

Radiation doses are unknown, frequency of response is very low. 

As radiation dose decreases, what happens to the required sample size?

 It increases.

How many people does your lecture estimate are needed to study effects at 5 rad (0.05 Gy)?

6 million

How many people are needed at 50 rad (0.5 Gy)?

100,000

What type of risk is the most common means of stating a risk?

Absolute Risk

What type of risk has a number of excess cases observed over what would be expected naturally in a population?

Excess Risk

What type of risk is used when the dose to which a population has been exposed is not precisely known?

Relative Risk

What type of dose-response relationship does acute radiation lethality follow?

Nonlinear threshold (sigmoidal)

What does LD50/30 mean?

 The whole-body radiation dose that causes death in 50% of exposed individuals within 30 days.

What does the 50 represent in LD50/30?

50% mortality

What does the 30 represent in LD50/30?

30 days after exposure

What is the human LD50/30 according to your lecture?

 3.5–4 Gy

What is the mouse LD50/30 according to your lecture?

 9 Gy

What does ARS stand for?

Acute Radiation Syndrome

What is ARS?

A series of symptoms and stages that can occur after high-dose whole-body radiation exposure (deterministic -cell death occurs)

What type of radiation effect is the most notable in ARS?

Deterministic effect

At what dose can ARS begin?

 Above approximately 1 Gy

What does N-V-D syndrome stand for?

Nausea, vomiting, and diarrhea

At what dose can N-V-D symptoms occur?

 0.5–1 Gy

What determines the severity of ARS?

 Total dose, dose rate, and distribution of radiation throughout the body.

What are the three acute radiation syndromes?

 Hematologic death, gastrointestinal (GI) death, and central nervous system (CNS) death.

 The initial ARS period when acute clinical symptoms appear after radiation exposure is called?

Prodromal period

 Nausea, vomiting, diarrhea, and leukopenia are symptoms of what ARS period?

Prodromal period

When do prodromal symptoms typically appear?

 Within hours after exposure.

How long can the prodromal period last?

A few hours to a few days.

What is the lowest dose at which prodromal symptoms can occur?

 1 Gy

How quickly can prodromal symptoms appear at doses greater than 10 Gy?

 Within minutes.

The ARS period following the prodromal stage when the individual appears free of symptoms.

Latent period

In which ARS period appears when the individual appears free of symptoms.

Latent period

What happens to symptoms during the latent period?

They temporarily disappear or decrease.

Does the latent period mean the individual has recovered?

No, the feeling of well-being may be mistaken for early recovery.

How long does the latent period last at high doses greater than 50 Gy?

 A few hours and can exist for a few days

How long does the latent period last at lower doses of 1–5 Gy?

 A few weeks

What is another name for hematologic syndrome?

Bone marrow or hematopoietic syndrome

At what whole-body dose does hematologic syndrome occur?

 Greater than 1 Gy

Why does hematologic syndrome occur at lower doses than GI and CNS syndromes?

Blood-forming stem cells in the bone marrow are highly radiosensitive.

When do prodromal effects occur in hematologic syndrome?

Within hours after overexposure

How long can the latent period last in hematologic syndrome?

Up to 4 weeks

What happens to peripheral blood cells during the latent period in hematologic syndrome?

 Their numbers decrease even though there are no obvious signs of illness.

What are the symptoms during manifest illness in hematologic syndrome?

Vomiting, mild diarrhea, malaise, anemia, fever, and infection.

What can cause death in hematologic syndrome?

 Generalized infection, dehydration, and electrolyte imbalance.

When does recovery begin if the dose is not lethal in hematologic syndrome?

2-4 weeks can take up to 6 months for full recovery

What is the only syndrome that can be rescued?

 hematologic syndrome

What whole-body dose range causes GI syndrome?

6–50 Gy

When do prodromal effects occur in GI syndrome?

Within hours

How long can prodromal effects last in GI syndrome?

 Several hours to one day

How long does the latent period last in GI syndrome?

 3–5 days

What is the most radiosensitive GI organ in GI syndrome?

Small intestine

What cells are responsible for producing the intestinal lining in GI syndrome?

Crypt cells

What happens when crypt cells are destroyed in GI syndrome?

The intestinal lining is lost, allowing blood plasma and electrolytes to enter the GI tract and intestinal bacteria to enter the bloodstream.

What are the symptoms during manifest illness in GI syndrome?

Nausea, vomiting, diarrhea, loss of appetite, and watery or bloody stools.

At doses below 10 Gy, how long does it take crypt cells to recover in GI syndrome?

About 1 week

When can death occur from GI syndrome?

4–10 days after exposure

At what whole-body dose does CNS syndrome occur?

Around 50 Gy

How quickly do initial symptoms appear in CNS Syndrome?

Within minutes

What are the initial symptoms of CNS Syndrome?

 Nausea, vomiting, nervousness, confusion, vision loss, and possible loss of consciousness.

How long is the latent period for CNS Syndrome?

6-12 hours

What are the symptoms during manifest illness for CNS Syndrome?

Disorientation, loss of muscle coordination, difficulty breathing, convulsive seizures, loss of equilibrium, ataxia, lethargy, and coma.

What is the ultimate cause of death in CNS syndrome?

Elevated fluid content of the brain.

How long can full recovery take for CNS Syndome?

Up to 6 months

What syndrome is the most radiosensitive?

CNS

What is the threshold dose for hematologic (bone marrow) syndrome?

1 Gy

What is the threshold dose for gastrointestinal (GI) syndrome?

 6 Gy

What is the threshold dose for central nervous system (CNS) syndrome?

50 Gy

What are the four stages of acute radiation syndrome?

Prodromal, latent, manifest illness, and recovery or death.

Which syndrome occurs at the lowest dose?

Hematologic

Which syndrome occurs at the highest dose?

CNS

What happens when only part of the body is irradiated?

A higher dose is required to produce an effect.

What tissues can be immediately affected by local radiation exposure?

Skin, gonads, and bone marrow.

What is erythema?

 Reddening of the skin.

What dose can cause initial mild erythema?

2 Gy

When can initial mild erythema appear?

Within the first or second day after exposure.

When does the second wave of erythema reach maximum intensity?

About 2 weeks after exposure.

What occurs at higher doses in local tissue damage?

Moist desquamation followed by dry desquamation, as described in the lecture.

What type of dose-response relationship do skin effects follow?

Nonlinear threshold

What is epilation?

 Loss of hair.

What is the threshold dose for epilation?

3 Gy

Are the testes and ovaries radiosensitive?

Yes

What dose can produce minimal detectable gonadal effects?

 100 mGy

What are examples of minimal gonadal effects?

Reduction in spermatozoa or suppression of menstruation.

What dose is associated with temporary sterility?

 Around 2 Gy

When can temporary sterility occur in males?

About 2 months after radiation exposure.

Is there temporary sterility in women?

No

Permanent sterility comes from what dose?

5 to 6 Gy

What does the hemopoietic system consist of?

Bone marrow, circulating blood, and lymphoid tissue.

What is the principal effect of radiation on the hemopoietic system?

Depression of the number of blood cells in the peripheral circulation.

What type of stem cell do all blood cells develop and mature from?

Pluripotential stem cell

Which blood cells are considered the most radiosensitive?

 Lymphocytes (white blood cells)

Why are lymphocytes considered the most radiosensitive blood cells?

 Possibly due to their large nucleus.

Which blood cells are the least radiosensitive?

Red blood cells