Fundamental Principles of Radiology

According to the Law of Bergonie and Tribondeau, stem cells are radiosensitive

True

According to the Law of Bergonie and Tribondeua, tissues with high metabolic activity are ______

Radiosensitive

Physical factors affecting radiosensitivity include:

• Linear Energy Transfer

• Relative Biologic Effectiveness

• Protraction

• Fractionation

Linear Energy Transfer

A measure of the rate at which energy is transferred from ionizing radiation to soft tissue

Linear Energy Transfer is expressed in

Kiloelectron volts per micrometer

LET is another method of expressing radiation quality

True

The LET of diagnostic x-ray is approximately _____ Kev per micrometer

3

The _____ of LET radiation, the greater the chance for a biological interaction/effect

Higher

Relative Biologic Effectiveness (RBE)

Measures the biological effectiveness of radiation having different LET’s

As the LET of radiation increases, so do the RBE

True

Diagnostic x-rays have an RBE of approximately

1

If a dose is delivered continuously, but at a lower rate, it is said to be ______

Protracted

Tissues are more radiosensitive when ______ is present

Oxygen

OER is LET dependent

True

OER is the greatest for _____-LET radiation

Low

Humans are most sensitive to radiation before birth

True

In old age, humans again become somewhat more radiosensitive

True

Human cells can recover from radiation damage if _____ death has not occurred

Interphase

Intracellular repair + repopulation =

Recovery

When a tissue or an organ receives a sufficient dose of radiation, it responds by shrinking. This is known as _____

Atrophy

Vitamin K is an example of a?

Radiosensitizer

The theory that suggest that a little bit of radiation is good for you is known as?

Hormesis

Stochastic response to radiation includes?

• low radiation exposure

• no threshold

______ dose-response curves suggest that the response to radiation exposure is directly proportional to the dose

Linear

_______ dose-response curves suggest that any dose, regardless of its size, is expected to produce a response

Nonthreshold

Radiation-induced malignancies, such as cancer and leukemia, and genetic effects follow a linear, nonthreshold dose-response curve

True

Nonlinear, threshold dose-response curves are also known as the :

Sigmoid dose-response curve

Radiosensitizers

Chemical agents that enhance the effects of radiation

Radioprotectors

Chemical agents that resist the effects of radiation, iodine pills

According the the Law of Bergonie and Tribondeau what is the most sensitive to radiation?

• immature, stem (precursor) cells

• undifferentiated cells

• rapidly dividing cells (high proliferation rate)

• younger tissues and organs

• tissues with high growth rate

• tissues with high metabolic activity

According to the Law of Bergonie and Tribondeau what is the most resistant to radiation?

• mature cells

• high differentiated (specialized) cells

Linear energy transfer (LET) is a measure of the _____ at which energy is transferred (deposited) from ionizing radiation to soft tissue

Rate

Linear energy transfer (LET) is a method of expressing radiation _____ and is used to determine the radiation weighing factor (Wr)

Quality

Linear energy transfer (LET) is measured in units of _____

keV/um

When LET is high, ionizations occur _____ increasing the probability of interactions with the target molecule

Frequently

Diagnostic x-ray has an LET of ____ keV/um and an RBE of ____

3, 1

Relative Biologic Effectiveness (RBE) is the degree of ____ or amount of biological change one can expect of the irradiated material

Response

Relative Biologic Effectiveness (RBE) is the amount of biological effect or _______

Biologic damage

What is the relationship between LET and RBE?

Direct

Dose protraction and fractionation cause _____ effect because time is allowed for intracellular repair and tissue recovery

Less

If the dose is delivered _____, but at a ____ dose rate, it is said to be protracted

Continuously, lower

If the dose is delivered at the same dose rate, but in equal fractions (separated by 24 hours), the dose is said to be _______

Fractionated

Dose fractionation is commonly used in __________

Radiation oncology

Tissue is most radiosensitive when oxygen is present

True

OER is ____ dependent and is ______for low-LET radiation

LET, highest

Biologic material is least sensitive to irradiation during _____ conditions

Anoxic

A human cell can recover from radiation damage is interphase death has occurred

False (has not occurred)

Includes stochastic effects such as radiation-induced cancer, leukemia, and genetic effects

Linear, nonthreshold

Any dose, regardless of its size is capable of producing a response and that response is not proportional to the dose

Nonlinear, nonthreshold

There is a minimum amount of radiation necessary before an effect will occur and if the dose doubles the response also doubles

Linear, threshold

ALARA guidelines are based off this dose-response relationship

Linear, nonthreshold

Is characteristic of a deterministic response and includes skin effects from high-dose fluoroscopy

Sigmoid (nonlinear, threshold)

There is no safe dose and that the dose is directly proportional to the response

Linear, nonthreshold

Which of the following line best represents the type of dose-response relationship that we are most concerned with in radiology? It represents stochastic effects such as leukemia, malignancies and genetic effects as well as ALARA and radiation safety practices

A

What type of dise-resposnse relationship is depicted by letter C?

Nonlinear-threshold

Which line best represents deterministic/early effects of radiation exposure?

C

Describe the linear, nonthreshold

• Most stochastic (late) effects

• ALARA

• Radiation-induced malignancies (most cancers and leukemia)

• Life-span shortening

• Genetic effects

• Effects in utero

• Some somatic effects

Describe nonlinear, threshold

• Most deterministic (early) effects

• Local tissue effects: skin, gonads, bone marrow

• Early skin effects from high-dose fluoroscopy (sigmoid type)

• Hematologic depression

• Radiation-induced cataracts (late effect)

• Acute radiation lethality

• Most somatic effects

What effects do protraction and fractionation have on irradiation?

• Allows more time for intracellular repair

• Allows more time for tissue recovery

OER is highest for _______-LET radiation

Low

Which of the following would have the highest LET, thus more frequent ionizations?

5 MeV Alpha Particle

How would you describe the relationship between LET and RBE?

Direct

Human cells can recover from radiation damage as long as interphase death has not occurred

True

Laws of Bergonie and Tribondeau

Younger tissues and organs are radiosensitive

Under what condition is biological tissue the most radio resistant to radiation exposure?

Anoxic

What has an RBE of 1?

Diagnostic x-rays

A radiation dose-reponse relationship is a mathematical relationship between various radiation dose levels and magnitude of the observed response

True

Current radiation protection guidelines and ALARA are based off this type of dose-response relationship

Linear, nonthreshold

Stochastic or late effects such as radiation induced malignancies, leukemia, and genetic effects follow this type of dose-response relationship

Linear, nonthreshold

Diagnostic radiology is primarily concerned with this type of dose-response relationship

Linear, nonthreshold