C. biological effects of radiation part 2 Flashcards
Dose-response relationships are represented by a
graph
Dose- response graphs show information on the cells response to radiation and cell survival in the
presence of radiation
Dose- response graphs are either
linear or nonlinear
___ graphs represent a response that is not proportional to the dose recieved
non- linear
____ graphs represents a response that is directly proportional to the dose recieved
linear
________ on a Dose-response graph represents a dose after which only 37 percent of the cell population will survive
Do or D37
Cells that are _____ have a low Do because it takes a lower dose to kill all but 37 percent of cell the cell population
radiosensitive
Cells that are ______ have a high Do because it takes a higher dose to kill all but 37 percent of the cell population
radioresistant
_______ is the number of cells or the target on dose response graph
extrapolation number (n)
The extrapolation number (n) is usually about
2-10
___ is the quasi-threshold dose, which represents the cells capability to repair
Dq
Dq is also known as the
shoulder region
Graphs with multipl Dq/ shoulder regions represent
multiple factors
_____ is the most sensitive part of the cell
DNA
where is DNA located
nucleus
When radiation interacts with the target it is called a
direct hit
Law of _________: explains the effect of radiation is greater for cells that divide rapidly, cells that are immature with long mitotic future, and undifferentiated
Bergonie and Tribondeau
Stem cells are ______ than mature cells
more radiosensitive
Blood forming cells are _____ because of their rapid division rate
more radiosensitive
_______ = the extent of radiation damage can change depending on the cells external factor before, during, or after delivery of radiation
Ancel and Vitemberger
________ is the rate that energy is deposited through matter as it travels through it
Linear energy transfer (LET)
LET is another expression of
radiation quality
X rays and gamma rays have ___ LET
low - goes farther
Protons and alpha particles have ___ LET
high - goes shorter distances
On a dose- response relationship graph, high LET is represented by a steeper curve and shoulder is either smaller than normal or nonexistent because more cells are
killed faster do not have a chance of repair
_________ = the ability for the type of radiation to produce biological damage
Relative biological effectiveness (RBE)
Higher LET= ___ RBE
higher
Lower LET = __ RBE
lower
let equations ??
Examples of radiation types with low RBE are
diagnostic x-rays, gamma rays, MV x-rays, electrons, etc.
Examples of radiation types with higher RBE are
heavy nuclei, alpha particles, fast neutron, etc.
Therapeutic ratio equation is
normally tissue tolerance dose / tumor lethal dose
On the linear accelerator, lower dose rates cause less damage than
higher dose rates
ideally, tumor lethal dose should be less than the normal tissue dose to avoid
damage to healthy tissue
High dose rates cause more
side effects more rapidly
TBI uses ___ dose rates
high
___ is the radiation dose than would cause 50% of population to die in 30 days
LD 50/30
LD 50/30= ___ SV
4-5
The presence of oxygen during a radiation treatment will greatly increase the
radiosensitivity of the cell
Tissues are more radiosensitive when in an
oxygenated, or aerobic, state
Typically, cells within a tumor are in an ___ state
Anoxic - no oxygen
_____ for xrays is 2.5-3.0 in human cells
Oxygen enhancement ratio (OER)
OER is higher for ___ LET radiation
Low
- due to high LET radiation already being very damaging
OER is lower for ___ LET radiation
high
A ______ effect is when radiation hits the target (DNA)
direct
A ____ effect is when radiation first hits water within the cell, which then damages DNA
indirect
Indirect effect lead to
radiolysis and free radicals in the cell
WHat is a common free radical in the cell
hydrogen peroxide ( H2O2)
Free radicals can lead to damage of
DNA
Chromosome damage can be
single or double strand breaks
_______ breaks can lead to dicentric fragments, acentric fragments, translocation and/or ring formation
single strands
_____ breaks can lead to deletions and inversion
double - stand
A cell response to radiation is cell death, which is known as
aptosis
The most radiosensitive cell cycle is th
M phase (also end of G2)
The most radioresistant cell cycle is the
S phase
