Rad Protection Ch.09

What is a radiation dose-response curve?

A graph showing the relationship between radiation dose received and the biologic response

What is the displayed on the horizontal axis of the dose-response curve?

Radiation dose

What is displayed on the vertical axis of the dose-response curve?

Biologic effect or response

As radiation dose increases, what generally happens to biologic effects?

Biologic effects generally increase

What is a threshold dose?

The radiation dose at which a biologic response first occurs

What is a threshold dose-response relationship?

A relationship in which there is a radiation dose below which no biologic effect is observed.

What occurs below the threshold dose?

No biologic effect is expected to occur

What is a non-threshold dose-response relationship?

A relationship in which any amount of ionizing radiation has the potential to produce a biologic effect

Can any dose of ionizing-radiation be considered absolutely safe?

No

What is a linear dose-response curve?

A curve in which the biologic response increases proportionally as radiation dose increases

What is a sigmoidal dose-response curve?

A curve in which the biologic response eventually reaches a maximum and levels off.

What are the two major categories of radiation tissue reaction effects?

Stochastic effects and non-stochastic effects

What are stochastic effects?

Effects in which the probability of occurrence increases as radiation dose increases, but the severity does not.

Does the severity of stochastic effect increase with dose?

No

What is stochastic effects also called?

Probabilistic tissue reactions

What increases with radiation dose for stochastic effects?

The probability that the effect will occur

What are two major stochastic effects?

Cancer and hereditary (genetic) effects

What type of dose-response curve do stochastic effects follow?

Non-threshold dose-response curve

Why is radiation protection important for stochastic effects?

Because every dose has the potential to produce a biologic effect

What are non-stochastic tissue reaction effects?

Harmful biological changes that happen when a threshold dose of radiation is passed.

What are non-stochastic tissue reaction effects also called?

Deterministic tissue reactions

What type of dose-response curve do non-stochastic effects follow?

Threshold-dose response curve

What happens below the threshold dose for deterministic effects?

The effect is not expected to occur

What happens after the threshold dose is exceeded?

The severity of the effect increases as radiation dose increases

Do deterministic effects become more severe with increases dose?

Yes

Name four non-stochastic (deterministic) effects

Sterility, organ atrophy, skin erythema, and cataracts

Which type of radiation effect does NOT have a threshold?

Stochastic effects

At approximately what dose does skin erythema begin to occur?

2-5 Gy

Is skin erythema expected below 2 Gy? Yes or No?

No

What does BEIR stand for?

Biological Effects of Ionizing Radiation

According to the BEIR report, most stochastic effects from low-LET radiation follow what type of dose-response curve?

Linear-Quadratic Non-Threshold

What’s the most important concept of the LQNT model?

Every radiation dose has the potential to produce a biologic effect

Which three effects are exceptions that are considered Linear Non-Threshold rather than Linear-Quadratic Non-Threshold in the notes?

Leukemia, breast cancer, and hereditary (genetic) effe

Why is the Linear non-threshold model considered more conservative?

It assumes every dose carries some risk

What type of radiation is considered low-LET in diagnostic imaging?

X-rays

Which type of radiation effect has increasing probability but not increasing severity?

Stochastic effects

Which type of radiation effect has increasing severity as dose increases?

Non-stochastic effects

Which type of effects are generally NOT expected from diagnostic x-ray doses?

Non-stochastic effects

Which type of biologic effect includes cancer?

Stochastic effects

Which type of biologic effect includes hereditary mutations?

Stochastic effects

Which type of biologic effect includes organ atrophy?

Non-stochastic effects

What should Rad Techs assume about every radiation exposure?

Every radiation exposure has the potential to produce a stochastic effect

Can late effects be somatic or hereditary? Yes or No?

Yes

What are examples of late effects?

Cataracts, cancer, and genetic DNA mutations

Can late effects be stochastic or non-stochastic? Yes or No?

Yes

Can late effects result from whole-body or partial-body exposure?

Yes

Can late effects result from chronic low-level radiation exposure?

Yes

What is epidemiology?

The science that studies the incidence, distribution, and control of disease in a population

How did researchers learn about many long-term radiation effects?

By studying populations exposed to high doses of radiation

What is considered low-level radiation exposure?

An absorbed dose of 0.1 Sv or less delivered over a short period of time. Or 0.5 Sv delivered over 10 years

Why is cancer risk from low-level radiation difficult to measure?

Because many other factors can also cause cancer- underlying disease, genetics, etc

What three major concerns remain for low-level radiation exoposure?

Cancer induction, fetal effects, and hereditary genetic effects

Can radiation exposure be fractionated?

Yes

What is fractionated radiation exposure?

Radiation received in separate exposures over time

Can radiation exposure be continuous?

Yes

What is an example of continuous radiation exposure?

Occupational exposure and natural background radiation

Why are radiologic technologists concerned about low-level radiation?

Because occupational exposure consists of repeated low-level doses.

Why do late effects occur?

Cells that survive radiation may retain damage that remains latent for years.

What is meant by latent damage?

Damage that remains inactive for years before becoming apparent.

Are non-stochastic (deterministic) effects likely from diagnostic x-ray exposure? yes or no?

No

Which late effects are considered possible from diagnostic x-rays?

Stochastic effects such as cancer and hereditary damage

Can cancer risk from diagnostic x-rays be measured directly?

No

Does increasing radiation dose increase the severity of cancer?

No

What does increasing radiation dose increase for cancer?

The probability of developing cancer.

What is relative risk?

A comparison of the number of effects in an exposed population to the number in an unexposed population

What does a relative risk of 1.0 indicate?

No increased radiation risk

What does a relative risk of 1.5 indicate?

A 50% higher response in the irradiated population

How does relative risk change as exposed populations age?

It increases because the latent period was passed

What is absolute risk?

The normal baseline risk of developing a disease

Does everyone already have some baseline risk of developing cancer? yes or no?

yes

What is excess risk?

Observed cases - expected cases

What are excess cases assumed to represent?

Radiation-induced cases

What is the threshold dose for radiation-induced cataracts according to our notes?

0.5 Gy

What dose may produce cataracts according to the textbook?

As low as 0.1 Gy

At what dose is there a high probability of cataracts?

Approximately 2 Gy

At what dose do nearly 100% of individuals develop cataracts?

10 Gy

Do cataracts follow a threshold or non-threshold relationship according to our notes?

Threshold

How does age affect lens radiosensitivity?

Radiosensitivity increases with age

How does age affect the latent period for cataracts?

The latent period becomes shorter

Which diagnostic imaging procedure delivers the greatest radiation dose to the eye?

CT

Should RTs wear leaded glasses?

yes

Has life span shortening been conclusively demonstrated in humans? yes or no?

no

has life span shortening been demonstated in animals studies?

yes

Is life span shortening still considered a possible radiation effect?

yes

What are teratogenic (antenatal) effects?

Radiation effects that occur to a developing fetus after conception

How radiosensitive is a fetus?

A fetus is always considered very radiosensitive, but becomes less radiosensitive as it develops

What are the three stages of gestation?

Preimplantation: 0-9 days after conception

Organogenesis: 10-12 weeks

Fetal Stage: 12 weeks- birth

Which trimester is the most radiosensitive?

The first trimester

Why is the first trimester highly radiosensitive?

Cells are immature stem cells that are rapidly dividing

What is the “Law of Bergonie and Tribondeau” as it applies to early pregnancy?

Rapidly dividing, immagure cells are the most sensitive to radiation.

What is the most likely effect of a high radiation dose during the first 2 weeks after fertilization ?

Prenatal Death (spontaneous abortion)

If a fetus survives high radiation dose during the first two weeks, what is most likely to happen?

It will likely develop normally without later radiation effects

What radiation dose during the preimplantation stage is most likely to cause fetal death?

0.05 - 0.2 Gy

After the preimplantation stage, what are radiation effects more likely to cause?

Developmental abnormalities rather than fetal death

What developmental abnormalities may result from fetal radiation exposure?

• Growth inhibition

• Mental retardation

• Microcephaly

• Genital deformities

  • Sense organ damage

During what weeks are skeletal deformities most likely to occur after radiation exposure?

3-20 weeks of gestation

What radiation effects are possible during the fetal stage (12 weeks to birth?

Childhood cancer and functional disorders

According to UNSCEAR, how much dose the risk of fetal abnormalities increase per rem of fetal dose?

0.3 % per rem

What’s the normal background risk of fetal abnormalities without radiation?

About 6%

Have low-level radiation doses been proven to increase fetal abnormalities above the normal risk?

No