CHAPTER 32 - CELLULAR RADIOLOGY

cellular transformation or cell death

The response of the cell is either _______ or _______.

cellular transformation

______ can result in a late stochastic effect at the human level.

deterministic effect

Cell death can result in an early __________ at the human level.

recovery and repair metabolic processe

Most effects on cells result in no response because of _________ and ________.

Radiation damage

___________ to such a molecule could affect the cell severely because no similar molecules would be available as substitutes.

target theory

Radiation damage to such a molecule could affect the cell severely because no similar molecules would be available as substitutes. This concept of a sensitive key molecule serves as the basis for the _________. According to the _________, for a cell to die after radiation exposure, its target molecule must be inactivated

DNA

______ is the target molecule.

Cell Lethality

Originally, the target theory was used to represent _________.

Target Theory

It can be used equally well, however, to describe nonlethal radiation-induced cell abnormalities

target

In the target theory the ______ is considered to be an area of the cell occupied by the target molecule or by a sensitive site on the target molecule.

Target

This area changes position with time because of intracellular molecular movement.

randomly

The interaction between radiation and cellular components is _______; therefore, when an interaction does occur with a target, it occurs ________.

hit

When radiation does interact with the target, a ______ is said to have occurred.

hit

Radiation interaction with molecules other than the target molecule also can result in a _____

not possible

It is _________ to distinguish between a direct and an indirect hit.

Hits

______ occur through both direct and indirect effects

indirect effect

When a hit occurs through ________, the size of the target appears considerably larger because of the mobility of the free radicals.

indirect effect of radiation.

When a hit occurs through indirect effect, the size of the target appears considerably larger because of the mobility of the free radicals. This increased target size contributes to the importance of the__________

low

With low-LET radiation, in the absence of oxygen, the probability of a hit on the target molecule is ______ because of the relatively large distances between ionizing events.

free radicals

If oxygen is present, _______ are formed and the volume of effectiveness surrounding each ionization is enlarged. Consequently, the probability of a hit is increased

high

When high-LET radiation is used, the distance between ionizations is so close that the probability of a hit by direct effect is ______.

does not result in additional hits

When oxygen is added to the system and high-LET radiation is used, the added sphere of influence for each ionizing event, although somewhat larger, _________.

bacteria

Early radiation experiments at the cell level were conducted with simple cells, such as ________.

cell cloning

If normal cells are planted individually in a Petri dish and are incubated for 10 to 14 days, they divide many times and produce a visible colony that consists of many cells. This is ____________.

fewer colonies

A higher radiation dose leads to the formation of ____________.

cell survival

The lethal effects of radiation are determined by observing __________, not cell death.

two models

When a mathematical extension of target theory is used, ________ of cell survival result.

single-target, single-hit model

The _________ applies to biologic targets, such as enzymes, viruses, and simple cells such as bacteria.

multi-target, single-hit model

The _________ applies to more complicated biologic systems such as human cells.

Radiation

_______ interacts randomly with matter.

wasted radiation dose

Just as with the wet squares, however, as the dose increases, some cells will sustain two or more hits. All hits per target in excess of one represent _______ because the bacteria had been killed already by the first hit.

inactivates

A hit is not simply an ionizing event but rather an ionization that ______ the target molecule.

D37

______ is a measure of the radiosensitivity of the cell.

low D37

A ______ indicates a highly radiosensitive cel

high D37

a _______ reveals radioresistance.

100%

If there were uniform irradiation (no wasted radiation), D37 would be sufficient to kill ______ of

the cells.

N0

_____ is the initial number of cells,

D37

_______ is a constant dose related to cell radiosensitivity.

more than a single critical target

Complex biologic specimens such as human cells are thought to have __________

inactivated

Suppose that the human cell has two targets, each of which has to be _____ for the cell to die.

100%

At very low radiation doses, cell survival is nearly ______.

both target molecules

At very low radiation doses, cell survival is nearly 100%. As the radiation dose increases, fewer cells survive because more sustain a hit in ________

single-target, single-hit model

At a high radiation dose, all cells that survive have one target hit. Therefore, at still higher doses, the dose-response relationship would appear as the __________

D0

The ____ is called the mean lethal dose

D0

_______ is a constant related to the radiosensitivity of the cell. It is equal to D37 in the linear portion of the graph and therefore represents the dose that would result in one hit per target in the straight-line portion of the graph if no radiation were wasted.

large D0

A ______ indicates radioresistant cells.

small D0

A _____ is characteristic of radiosensitive cells.

target number

The extrapolation number is also called the _______.

2

The extrapolation number is also called the target number. When this type of experiment was first conducted with human cells, the observed extrapolation number was _____.

DQ

The ______ is called the threshold dose.

D_Q

It is a measure of the width of the shoulder of the multi-target, singlehit model and is related to the capacity of the cell to recover from sublethal damage

D_Q

large

A ______ DQ indicates that the cell can recover readily from sublethal radiation damage.

multi-target, single-hit model

The shoulder of the graph of the __________ shows that for mammalian cells, some damage must be accumulated before the cell dies

sublethal damage

The shoulder of the graph of the multi-target, single-hit model shows that for mammalian cells, some damage must be accumulated before the cell dies. This accumulated damage is called ________.

more sublethal damage

The wider the shoulder, the _______ that can be sustained and the higher the value of DQ.

D_Q

_______ is a measure of the capacity to accumulate sublethal damage and the ability to recover from sublethal damage.

cell-cycle time

When human cells replicate by mitosis, the average time from one mitosis to another is called the __________.

24 hours

Most human cells that are in a state of normal proliferation have cell-cycle times of approximately _______

G1 phase

Longer cell-cycle times primarily result from lengthening of the ______ of the cell cycle.

G1

______ is the most time variable of cell phases.

synchronized

A randomly growing population of cells that are uniformly distributed in position throughout the cell cycle can be ________ in various ways.

M phase

Human cells are most radiosensitive in _____ and most radioresistant in late S.

late S phase

Human cells are most radiosensitive in M phase and most radioresistant in _______.

mitosis

Cells in ______ are always most sensitive.

mitosis

The fraction of surviving cells is lowest in this phase.

G1–S transition

The next most sensitive phase of the cell cycle occurs at the _______.

late S phase

The most resistant portion of the cell cycle is the ________.

oxygen

Mammalian cell survival experiments have been used extensively to measure the effects of various types of radiation and to determine the magnitude of various dose-modifying factors, such as ______

effectiveness of the dose modifier

D0, is related to radiosensitivity, the ratio of D0 for one condition of irradiation compared with another is a measure of the ___________, whether it is physical or biologic.

single-target, single-hit model

At very high LET (as with alpha particles and neutrons), cell-survival kinetics follow the ____________.

multi-target, single-hit model

With low-LET radiation (x-rays), the_______________ applies.

single-target, single-hit model

Irradiation of mammalian cells with high-LET radiation follows the ____________.

greater than

The mean lethal dose after low-LET irradiation is always _________ that after high-LET irradiation.

oxygen

The most completely studied dose modifier is __________.

oxygen

The presence of ________ maximizes the effect of low LET radiation

anoxic

When _______ cells are exposed, a considerably higher dose is required to produce a given effect.

high-LET radiation

With __________, little difference is noted between the response of oxygenated cells and that of anoxic cells.

target theory

The concept of a sensitive key molecule within a cell serves as the basis for the _____________.

DNA

For a cell to die after radiation exposure, the target molecule, ______, must be inactivated.

bacteria

The single-target, single-hit model applies to simple cells such as ________.

dose threshold

The multi-target, single-hit model implies a ________.

single-hit, single target model

at higher doses, the relationship becomes a _____________.

sublethal radiation damage

Experiments in cell recovery show that cells can recover from _______________.