Radiobiology - Exam 4

What is another term for Acute Radiation Syndrome?

Acute Radiation Sickness

Death occurring within a few weeks after a specific, high-exposure to radiation

Early radiation lethality

What dose the magnitude of dose decide?

* Survival time
* Mode of death

What is an “end-point” for scoring radiation death?

Lethal Dose (LD)

The whole body dose of radiation that will result in death of 50% of the exposed population in 60 days?

LD50/60

What is the LD50/60 dose with bone marrow transportation?

11 Gy

Radiation dose exceeding what are generally fatal?

12 Gy

No record of a human surviving above how many Gy?

10 Gy

When is ARS possible?

* Radiation dose is high
* The dose source is external
* Rad type is sufficiently penetrating
* A whole body dose was received
* Acute dose delivery occurs

What is the minimum dose required for ARS?

* Must be greater than 0.7 Gy
* Mild symptoms possible at 0.3 Gy

What type of ionizing radiation can cause ARS?

* X-rays
* Gamma
* Alpha
* Fast neutrons

What are the stages of ARS?

* Prodromal stage
* Latent period
* Manifest Illness stage
* Recovery or death

What is another term for prodromal stage?

Nausea-vomiting-diarrhea (NVD) stage

A period of early symptoms occurring immediately after radiation exposure?

Prodromal stage

What is the minimum dose that causes the prodromal stage?

1 Gy

What stage follows the prodromal stage?

Latent Period

How long can the latent period last?

Few hours to a few days

What are the 3 distinct syndromes of the manifest illness stage?

* Hematopoietic
* Gastrointestinal
* Cerebrovascular

What is another term for hematopoietic syndrome?

“Bone Marrow Syndrome”

At what dose does the hematopoietic syndrome occur?

0\.7-10 Gy

What happens to survival rate as the dose increases?

Decreases

How long is the latent period in hematopoietic syndrome?

Up to 4 weeks

Manifest illness of hematopoietic syndrome?

* Anorexia, fever, malaise
* Destruction of bone marrow, anemia, infection, hemorrhage

Recovery of hematopoietic syndrome?

Bone marrow regeneration

At what dose does the gastrointestinal syndrome occur?

Between 6-10 Gy

How long is the latent period in gastrointestinal syndrome?

Lasts less than 1 week

Recovery of gastrointestinal syndrome?

Death within 2 weeks due to infection, dehydration, and electrolyte imbalance

At what dose does the cerebrovascular syndrome occur?

Total body dose greater than 50 Gy

How long is the latent period in cerebrovascular syndrome?

Hours at most

Recovery of cerebrovascular syndrome?

Usually within 3 days of exposure

As dose increases, what happens to the latent period?

Decreases

What are different examples of somatic effects?

* Erythema
* Epilation
* Gonads
* Cataractogenesis

At what dose does erythema occur?

Possible at 2 Gy (within 24-48 hours)

Doses of 5 Gy or greater result in what?

Erythema followed by vasodilation and edema

High dose erythema is followed by?

* Desquamation
* Ulceration

Shedding of skin in sheets (AKA sloughing)?

Desquamation

Sore; open lesion (complete loss of epidermis)?

Ulceration

Short, thin hair because of radiation exposure?

Hair dysplasia

Loss of hair?

Epilation

When does epilation occur after exposure?

3 weeks after

When does hair regrowth occur after epilation?

1-3 months

Observed responses of the gonads are observed at what dose?

0\.1 Gy

Temporary sperm count reduction is possible at what dose?

0\.1 Gy

Temporary sperm sterility is possible at what dose?

0\.15 Gy

No measurable sperm in semen?

Azoospermia

At what dose does azoospermia occur?

2 Gy (permanent azoospermia occurs at 5-6 Gy)

At what dose can delayed or suppressed menstruation occur?

0\.1 Gy

Temporary sterility of oocytes is possible at what dose?

2 Gy (permanent sterility occurs at 5-6 Gy)

An opacification of the lens of the eye?

Cataract

How is cataractogenesis classified?

By degree of opacity

What type of radiation effect are cataracts?

A late, deterministic effect of radiation

What is the latent period of cataracts?

6 months-35 years

Induced by radiation exposure before or just after implantation of the embryo into the uterine wall (preimplantation)?

Lethal Effects

Common when dose occurs during period of fetal organogenesis?

Malformations

Common when dose occurs later in pregnancy (fetal period)?

Growth Disturbances

Which trimester is the most radiosensitive?

1st Trimester

Which trimester is the key stage of organogenesis?

1st Trimester

When is the greatest risk of radiation-induced death?

3-6 weeks

What dose is considered therapeutic abortion?

0\.1 Gy during the 1st trimester

Irradiation at 4-11 weeks of gestation will cause what?

Severe abnormalities of the organs

Irradiation at 11-16 weeks will cause what?

Abnormally affect the developing eyes, skeleton, and genital organs

Irradiation at 16-25 weeks will cause what?

May lead to minor microcephaly, mental retardation, and stunted growth

Irradiation at 30 weeks will cause what?

May cause functional disabilities (physiological and cognitive)

Exposures less than what are considered safe for embryo’s in utero?

0\.05 Gy

Graphically illustrates the relationship between the observed effects of radiation exposure and the dose recieved?

Dose-Response Curves

What are the 2 classification of curves?

* Linear or non-linear
* Threshold or non-threshold

What is the relation between biologic response with stochastic effects?

Proportional to the dose

No known level of dose at which 0 response occurs?

No threshold

Which relationship curve demonstrates most cancers and is the basis of the ALARA principle?

Linear Non-Threshold Dose - Response Relationship (LNT Model)

Which relationship curve illustrates the relationship between exposure to low levels of radiation?

Linear-Quadratic Non-Threshold Dose - Response

What do use the Linear-Quadratic Non-Threshold Dose model to show?

* Some cancer
* Genetic disease

If you increase dose in the Linear-Quadratic Non-Threshold Dose relationship, what happens to the probability of response?

Increases

What does Non-Threshold mean?

No “safe dose”

What is another term for tissue reaction?

* Deterministic
* Non-stochastic

Some level of dose below which a response does not occur

Threshold

Biologic response is observed with increasing severity as dose increases?

Beyond Threshold Dose

Skin damage, cataracts, infertility, and hematologic effects are all what kind of effects?

Somatic

When the curve starts to level off, what does this mean?

The biological response cannot become any more severe

Which relationship curve demonstrates tissue reactions?

Non-Linear Threshold Dose - Response Relationship

This relative risk model illustrates dose risk relationships for individuals who are hypersensitive to radiation based on predisposing (genetic) factors?

Supra-Linearity

This relative risk model uses the LNT model relative to natural cancer risk (most cancers)?

Linear

This relative risk model uses the non-linear relative to natural risk (leukemia, breast cancer, genetic effects)?

Linear-Quadratic

This relative risk model demonstrates low dose radiation as a means of stimulating natural repair mechanisms that protect against disease (cancer)?

Hormesis

This accounts for the natural occurrence of cancer, unrelated to radiation exposure and illustrate how dose adds additional risk (disease incidence)?

Relative Risk Models

The most severe consequence of cell exposure to radiation?

Lethal damage

At what type of doses of radiation can biological damage be reversed?

Low to medium

The increase in cell survival that is observed if a given radiation dose is split into 2 fractions, separated by a time interval

Sublethal damage (SLD)

Dividing a total dose into a number of fraction administered over time, allowing for the repair of sublethal damage?

Fractionation

Dose delivered continuously over a long period of time (occupational radiation exposure)?

Protraction

When does repair happen in SLD?

Usually within hours

The post-exposure environment must be manipulated to offer hope of survival?

Potentially lethal damage (PLD)

Who said “Ionizing radiation may be essential for life”?

T.D. Luckey (1950)

Exposure at or just above the normal background rate may be beneficial?

Hormesis Theory

What are the 4 classifications of biological effects?

1. Somatic
2. Genetic
3. Stochastic
4. Tissue Reactions

Biologic damage to the exposed individual?

Somatic effects

What are short-term somatic effects?

* Nausea
* Erythema
* Epilation

What are long-term somatic effects?

* Cancer
* Cataracts
* Embryologic (birth defects)

Biologic damage expressed in the future generation(s) or offspring of the exposed?

Genetic effects

Biologic damage that is random in nature?

Stochastic effects

In stochastic effects, the chance of occurence is proportional to what?

The dose of radiation (not the severity)