4.2 Fundamental Principles of Radiobiology Flashcards by Dana Athena Augusto

if the dose is delivered continuously but at a lower dose rate, it is
said to be _____
-When 6 Gyt is delivered at the rate of 10 mGyt/hr for a total time of 600
hours, the mouse will survive

protracted

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If the 6-Gyt dose is delivered at the same dose rate, but in 12 equal fractions
of 500 mGyt, all separated by 24 hours, the mouse will survive. In this
situation, the dose is said to be _____

fractionated

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Six gray (600 rad) delivered in 3 -minutes at a dose of 2 Gyt/min is \_\_\_\_ for
a mouse

lethal

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The response of biologic tissue to radiation is ____ when irradiated in the oxygenated, or aerobic, state than when irradiated in anoxic or hypoxic conditions.

greater

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OER (oxygen enhancement ratio)=

OER= dose necessary under anoxic conditions to produce a given effect / dose necessary under aerobic conditions to produce the same effect

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is defined as the
dose of radiation that produces a given biologic response under
anoxic conditions divided by the dose of radiation that produces the
same biologic response under aerobic conditions.

oxygen enhancement ratio (OER)

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It is theorized that
oxygen is needed in order for free radicals to form during ionization
of water. Without the free radicals, hydrogen peroxide is not formed,
and thus cell damage is _____

reduced

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OER depends on ____

LET

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The OER is most pronounced for ___

LET radiation, and is less effective with __ LET radiation

most - low,

less - high

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Because of the physical differences between high and low LET radiation, the quantity of damage done by high LET radiation would
be beyond repair. Thus, having oxygen present would not _____
the response to radiation to the same magnitude, as would be the case with low LET radiation

intensify

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Humans are most _____
before birth and are most
____ during
maturity

sensitive,

radioresistant

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With old age, humans again tend to become more _____

radiosensitive

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Tissue is more sensitive to radiation when irradiated in the oxygenated state than when irradiated under anoxic (without oxygen) or hypoxic (low-oxygen) conditions.
This characteristic of tissue radiation response is called
the _____ and is described numerically by the
_____

oxygen effect,

oxygen enhancement ratio (OER)

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without oxygen

anoxic

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low-oxygen

hypoxic

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high-pressure

Hyperbaric

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has been used in radiation oncology in an attempt to enhance the radiosensitivity of nodular, avascular tumors, which are less radiosensitive than tumors
with an adequate blood supply

Hyperbaric (high-pressure)

oxygen

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The OER is highest for low-LET radiation, with a maximum value of approximately __ that decreases to approximately __ for high-LET radiation

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a decrease in the size of a tissue or organ due

to cellular shrinkage

cell atrophy

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In vitro experiments show that if dose is not sufficient to induce interphase death, then cell will be able to _____

recover

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occurs when the cell dies before replicating

Interphase death

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At the whole-body

level, this recovery from radiation damage is assisted through _____ by surviving cells

repopulation

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If a tissue or organ receives a sufficient radiation
dose, it responds by shrinking. This is called ____, and it occurs because some cells die and disintegrate,
and are carried away as waste products

atrophy

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Recovery =

Recovery = Intracellular repair + Repopulation

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agents that enhance the effect of radiation

Radiosensitizers

halogenated pyrimidines, methotrexate, actinomycin D, hydroxyurea, and vitamin K

Radiosensitizers

become incorporated | into the DNA of the cell and amplify the effects of radiation on that molecule

halogenated pyrimidines

include molecules that | contain a sulfhydryl group (sulfur and hydrogen bound together), such as cysteine and cysteamine

Radioprotectors (Radioprotective compounds)

have not found human application because, to be effective, they must be administered at toxic levels. The protective agent can be worse than the radiation

Radioprotective agents

A separate and small body of radiobiologic evidence suggests that a little bit of radiation is good for you

Hormesis

Interactions with Radiation

- Radiolysis of Water - Irradiation of Macromolecules - Single-Hit Chromosome Aberrations - Multi-Hit Chromosome Aberrations - Reciprocal Translocations

When an atom of water is irradiated this ionizes the water, and produces a free radical

Radiolysis of Water

an uncharged molecule that contains a single unpaired | electron in its outermost or valence shell, which makes it chemically unstable and highly reactive

Free Radical

Reactions of water include:

1. H2O + radiation = HOH+ + e- 2. H2O + e- = HOH– 3. HOH+ = H+ + OH* 4. HOH- = OH- + H* 5. OH* + OH* = H2O2 6. H* + O2 → HO*2 7. HO*2 + HO*2 → H2O2 + O2

occurs when an atom has an extra electron, or has had an electron removed

Ionization

If an ion has more electrons than it does protons, it is designated with a _____ sign. If an ion has more protons than electrons, it is designated with a ____ sign

negative, | positive

The occurrence of molecular derangements or lesions may be classified as either effects on _____ or effects on _____

macromolecules, | water

If macromolecules are exposed to ionizing radiation ___, a significant dose of radiation is needed to produce a measurable effect

in vitro

Irradiating macromolecules ___ shows that when cells | are in their natural conditions, they are much more radiosensitive

in vivo

The three primary effects of irradiating macromolecules in vitro include

main-chain scission, cross-linking, and point lesions

occurs when the thread | or backbone of the long-chain molecule is broken

Main-Chain Scission

This results in the long-chain molecule being reduced to numerous smaller molecules, which can still be macromolecular in nature. Not only is the size of the macromolecule reduced, but its viscosity is also reduced

Main-Chain Scission

Some macromolecules have small, spur-like side structures that extend off the main chain. Others produce these spurs as a consequence of irradiation

Cross Linking

Others develop these spurs after being irradiated. After being irradiated, these spurs can act as if they had sticky material on their ends. These spurs can attach to neighboring macromolecules or to another segment of the same molecule. This stickiness causes the macromolecule to connect to another macromolecule, or to another section of the same molecule

Cross Linking

is increased by | radiation-produced molecular cross-linking

Viscosity

Radiation interaction with macromolecules also can result in disruption of single chemical bonds, producing ____

Point Lesions

may cause slight molecular changes, | which in turn cause the cell to function incorrectly

Point Lesions

At low doses of radiation, _____ are regarded to be the cellular radiation damage that is responsible for the late radiation effects, which are observed at the whole-body level

Point Lesions

are not detectable, but they can cause a minor modification of the molecule, which in turn can cause it to malfunction within the cell.

Point Lesions

its radiosensitivity is midway between that of DNA and protein macromolecules

RNA

These molecular genetic mutations are termed _____, and are common with low LET radiations

Point mutations

may be either of minor or major significance to the cell. A very major effect of these point mutations would be the genetic code being incorrectly transferred to daughter cells.

Point mutations

When chromosomes are irradiated, the interaction can be either direct or indirect. The result of either interaction is called a __

hit

Chromosome hits cause a ____ chromosome change. Such a hit would mean that numerous molecular bonds had been interfered with, and that several chains of DNA had been severed

visible

breakage of a chromatid

chromatid deletion

can occur in G1 phase and G2 phase of cell cycle

Single-Hit Chromosome Aberrations

During the S-phase of the cell cycle, the deletion and the remaining chromosome are replicated. The chromosome abnormality that is seen during metaphase is a normal-appearing chromosome with material missing from the ends of two sister chromatids and two acentric fragments. Such fragments are called _____

isochromatids

There is a ___ probability that ionizing radiation will pass through sister chromatids to produce isochromatids

low

A single chromosome can sustain more than one hit

Multi-Hit Chromosome | Aberrations

are not uncommon,

Multi-Hit Chromosome | Aberrations

During the G1 phase of the cell cycle, if two hits occur on one chromosome, _____ are produced

ring chromosomes

When neighboring chromosomes each suffer one hit and then recombine, this produces ____

dicentrics

a chromosome with two centers or two centromeres

dicentric

The quality of the _____ present at the severed chromosome is the determining factor for the joining of the chromatid

stickiness

During the __ phase of the cell cycle, similar chromosomal abnormalities can occur. These types of aberrations are rare, as they require that the same chromosome is hit two or more times, or that neighboring chromosomes are hit and join together

are representative of major | cell damage

Multi-Hit Chromosome | Aberrations

are multi-hit chromosomal aberrations

Reciprocal translocations

If chromosomes experience this type of alteration, they do not lose any genetic material, but instead the genes become rearranged. This results in all genetic codes being available, but sequenced incorrectly

Reciprocal translocations

At the doses received in diagnostic radiology, only _____ types of chromosomal aberrations are seen

single-hit

If the radiation dose is not known, the approximate chromosomal aberration frequency will be:

-two single-hit aberrations/rad/1,000 cells, -one multi-hit aberration/ 10 rad/1,000 cells