ch 35 unit 3 Deterministic Effects of Radiation: Effects, Syndromes, and Tissue Damage

What are deterministic radiation effects?

Radiation effects that have a threshold and increase in severity as radiation dose increases; they follow a nonlinear dose-response curve.

When do early deterministic effects occur?

Relatively soon after exposure - within minutes, hours, days, or weeks - after substantially high doses.

What are two deterministic effects that may be relevant to diagnostic imaging?

Lymphocytic depression and skin responses.

What are examples of early deterministic somatic effects?

Nausea, fatigue, erythema, epilation, blood disorders, intestinal disorders, fever, desquamation, depressed sperm count, sterility, and CNS injury at extremely high doses.

What is epilation?

Loss of hair.

What is desquamation?

Shedding of the skin; it may be dry or moist.

What is Acute Radiation Syndrome (ARS)?

Radiation sickness caused by a large whole-body radiation dose received in a short period of time.

Are diagnostic x-rays whole-body exposures?

No. Diagnostic x-rays are always partial-body exposures.

What are the three dose-related syndromes of ARS?

Hematologic (bone marrow) syndrome, gastrointestinal syndrome, and central nervous system syndrome.

What are the four major response stages of ARS?

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

How is the severity of ARS related to dose?

Severity is dose related; increasing dose produces more severe effects.

What is the prodromal period?

The near-immediate stage after more than 1 Gy total-body exposure, with symptoms appearing within minutes to hours.

What are common symptoms of the prodromal period?

Nausea, vomiting, diarrhea, and leukopenia.

How long does the prodromal period last?

Hours to days.

What happens to prodromal symptoms above 10 Gy?

Symptoms become violent, and at even higher doses the person progresses to manifest illness.

What is the latent period?

The stage after the prodromal period when no symptoms are evident and the person may appear well.

How does dose affect the length of the latent period?

At 1-5 Gy it can last for weeks; above 50 Gy it may last only hours or less.

What total-body dose is associated with hematologic syndrome?

About 2-10 Gy.

What happens to blood counts during hematologic syndrome?

Red blood cells, white blood cells, and platelets decrease because bone marrow cells are destroyed.

What major risks result from hematologic syndrome?

Decreased ability to fight infection and increased risk of hemorrhage.

How long can recovery from a nonlethal hematologic dose take?

Recovery may begin in 2-4 weeks and can take up to 6 months.

What treatment may help in hematologic syndrome?

A bone marrow transplant may help.

How does increasing dose affect survival time in hematologic syndrome?

As dose increases, survival time decreases.

What total-body dose is associated with gastrointestinal syndrome?

About 10-50 Gy.

What are manifestations of gastrointestinal syndrome?

Nausea, vomiting, diarrhea, fever, fatigue, anemia, infection, and hemorrhage.

What causes death in gastrointestinal syndrome?

Catastrophic damage to GI epithelial cells causes infection, fluid loss, and electrolyte imbalance; intestinal crypt stem cells die and cannot regenerate the lining.

What is the typical survival time for gastrointestinal syndrome without medical care?

About 4-10 days.

Is survival time in gastrointestinal syndrome affected by dose?

No. The chapter states that survival time is not affected by dose.

What total-body dose is associated with central nervous system syndrome?

50 Gy or more.

What are prodromal symptoms of CNS syndrome?

Excessive nervousness, confusion, nausea/vomiting, diarrhea, loss of vision, burning sensation on the skin, and loss of consciousness.

How long is the latent period in CNS syndrome?

About 12 hours.

What occurs during manifest illness in CNS syndrome?

Prodromal symptoms become more severe, with seizures, coma, meningitis, and prostration.

What is the cause of death in CNS syndrome?

Damaged blood vessels in the brain increase intracranial pressure.

How quickly can death occur with CNS syndrome?

Within a few hours to 2 or 3 days.

Why do hematologic and GI syndromes not occur in severe CNS syndrome?

Death occurs too quickly for those syndromes to develop.

What happens to mean survival time as total-body radiation dose increases?

The average time between exposure and death decreases.

What does LD50/60 mean?

The whole-body radiation dose that can be lethal to 50% of an exposed population within 60 days.

What is the estimated LD50/60 for adult humans?

About 3.0-4.0 Gy, with 3.5 Gy given as the approximate value.

What could a 6 Gy whole-body dose cause?

LD100/30, although medical intervention could help.

What is local tissue damage?

A response in an organ or tissue caused by partial-body exposure.

Does local tissue damage generally require a higher or lower dose than whole-body effects?

A higher dose than a whole-body exposure.

How does local tissue damage progress?

Cell death can lead to tissue or organ atrophy and then either total loss of function or recovery.

What are examples of tissues affected by local radiation damage?

Skin, gonads, and bone marrow.

What type of dose-response relationship does local tissue damage have?

A nonlinear, threshold dose-response relationship; severity increases as dose increases.

What was the first radiation unit used for skin effects?

Skin Erythema Dose (SED).

What is SED50?

The skin erythema dose required to affect 50% of those irradiated; the chapter gives about 5 Gy.

Why is the skin susceptible to radiation injury?

The skin is a continuing cell-renewal system, and its basal cells are stem cells that can be injured by radiation.

What is erythema?

Sunburn-like reddening of the skin.

When can early and main-wave erythema appear?

Early erythema can appear within the first day; the main or second wave can appear within 10-14 days.

What can erythema progress into at higher doses?

Desquamation, including moist and dry desquamation.

Why is high-dose fluoroscopy a concern?

Because of its potential to produce skin effects.

Which female germ-cell stage is most radiosensitive?

The oocyte in the mature follicle, while preparing to resume meiosis.

Which male germ cells are most radiosensitive?

Spermatogonia, because they are undifferentiated and mitotically active.

What gonadal effects may occur around 100 mGy?

Menstruation may be delayed or suppressed, and spermatozoa may be reduced.

What gonadal effect is associated with about 2 Gy?

Temporary infertility.

What gonadal effect is associated with about 5 Gy?

Permanent sterility.

Is sterility a major concern in diagnostic imaging?

The chapter states that sterility is essentially not a concern in imaging, although chromosomal aberrations may be possible.

Where do radiation-induced cataracts form?

On the posterior pole of the lens.

How does age affect lens radiosensitivity according to the chapter?

The greater the age, the greater the effect, and the latent period is shorter.

What latent period is given for radiation-induced cataracts?

About 5-30 years, with an average of 15 years.

What threshold is given for acute radiation-induced cataracts?

About 2 Gy, or up to 10 Gy if the dose is fractionated.

What is the minimum whole-body dose for hematologic depression?

250 mGy.

What structures make up the hematopoietic system?

Bone marrow, circulating blood, and lymphoid organs such as the lymph nodes, spleen, and thymus gland.

From what type of cell do hematopoietic cells develop?

A single precursor called a pluripotential stem cell.

Where are most circulating blood cells manufactured?

In the bone marrow.

What is the principal hematologic response to radiation?

A decrease in the number of a blood cell.

Which blood cells are the most radiosensitive?

Lymphocytes; their numbers decrease quickly after exposure.