Chapter 7 Flashcards
Molecular & Cellular Radiation Biology
What are four things that may occur if a cell is damaged by radiation?
-Cell may repair itself completely
-Cell may partially repair itself but not able to function correctly
-Cell may continue to function but will pass on incorrect genetic information
-Cell may die
What is chromosome aberration(or mutation)?
Any permanent damage to chromosomes
If somatic cells are involved in chromosome aberration, what will it result in?
-Loss of function, malignancy (cancer), or even death
-Affects only the person irradiated
If gonadal cells are involved in chromosome aberration, what will it result in?
-Mutations in future generations
-Affects future generations
What is radiation biology?
Branch of biology concerned with the effects of ionizing radiation on living systems
What is ionizing radiation?
Damages living systems by ionizing the atoms comprising the molecular structure of these systems
What does biologic damage begin with?
The ionization produced by various types of radiation
What are examples of radiation that produces ionization?
-X-rays
-Gamma Rays
-Alpha Particles
-Beta Particles
-Protons
Ionized atom will or will not bond properly in molecules?
Will not
What are determinants of radiation energy transfer?
-Charge, mass, and energy vary among the different types of radiation
These attributes determine the extent to
which different radiation modalities transfer
energy into biologic tissue
What are three important concepts to help us understand the way ionizing radiation causes injury and how the effects may vary in biologic tissue?
-Linear energy transfer
-Relative biologic effectiveness
-Oxygen enhancement ratio
What is LET (Linear energy transfer)?
A measure of the rate at which energy is transferred from a beam of ionizing radiation to the tissue through which it is traveling
How is LET measured?
Measured in kiloelectron volts (keV) of energy transferred per micrometer of tissue
What is LET very important factor for?
Assessing potential tissue and organ damage from exposure to ionizing radiation
What is the LET for diagnostic x-rays?
About 3keV/micrometer
As LET increases, what happens to biological damage and radiation damage?
They both increase
What happens to LET if there is an increase in the ability to penetrate?
Decreases
What are the two radiation categories according to LET?
-Low-linear energy transfer radiation
-High-linear energy transfer radiation
What are Low-LET radiation?
-Gamma rays
-X-rays
What are High-LET radiation?
-Alpha particles
-Ions of heavy nuclei
-Charged particles released from interactions between neutrons and atoms
-Low-energy neutrons
What is relative biologic effectiveness (RBE)?
Takes into consideration the amount of damage caused by different types of radiation
Radiation with higher LET will cause _____ biological damage.
more
An increase in LET will cause RBE to?
Increase
LET & RBE are proportional
What RBE does x-rays have?
1
What is oxygen enhancement ratio (OER)?
The ratio of the radiation dose required to cause a particular biologic response of cells or organisms in any oxygen-deprived environment to the radiation dose required to cause an identical response under normal oxygenated conditions
X-rays and gamma rays have an OER of?
About 3.0 when radiation does is high
Biologic tissue is _______ radiosensitive when it is well oxygenated, than when it is poorly oxygenated (hypoxic).
MORE
What are the three levels biologic damage stemming from exposure to ionizing radiation may be observed?
-Molecular
-Cellular
-Organic systems
If there is any visible radiation-induced injuries of living systems at the cellular or organic level, it began with?
With damage at the molecular level
What does molecular damage result in?
The formation of structurally changed molecules that may impair cellular functioning
What are the effects of irradiation on cells?
it may disturb the cell’s chemical balance and ultimately the way it operates. The affected cell can then no longer perform its normal task.
What happens if a sufficient quantity of somatic cells are affected by irradiation?
The entire body processes may be disrupted
What happens if radiation damages the genetic cells?
The damage may be passed on to future generations in the form of genetic mutations
What are the two classifications of ionizing radiation interaction on a cell?
-Direct Effect (e.g., in DNA)
-Indirect Effect (e.g., in H2O)
What classification of ionizing radiation interaction do essentially all effects of low-LET irradiation in a living cell result from?
Indirect
- Because the human body is 80% water and less than 1% DNA
What is direct effect?
a photon form the primary beam of radiation ionizes a molecule critical to the cell (ex. DNA)
What is indirect effect?
After an initial ionizing event, there will be an ejected electron and either a secondary or scattered photon that may ionize another atom or molecule (H2O)
Does Direct or Indirect cause the most radiation damage?
Indirect
What happens to water when it is irradiated?
It easily breaks down into molecular products
When water breaks into molecular products, these molecules can break down into?
Ions of hydrogen(H), hydroxyl molecules(OH), & a free electron
What can the ions of hydrogen, hydroxyl molecules and a free electron recombine as?
Harmless-
H20 (water) or H30 (heavy water)
Harmful (Toxic in large enough quantities can kill the cell-
H202 (hydrogen peroxide)
A cell can absorb radiation damage and continue to function unless what is damaged?
a key or target molecule(DNA)
What happens if the target molecule is damaged?
the cell will die
What is necessary for the survival of the cell?
Master, or key molecule
What can target theory be used to explain?
Cell death and nonfatal call abnormalities caused by exposure to radiation
What percentage of mutations are harmful?
99.9%
What are the 6 ways damage to the cell’s nucleus reveals itself?
-Instant death
-Reproductive death
-Apoptosis, or programmed cell death (interphase death)
-Mitotic, or genetic, death
-Mitotic delay
-Interference with function
When does instant death in large numbers of cells occur?
When a volume is irradiated with an x-ray or gamma ray dose approx. 1000gy
What is gross distribution caused by?
The cell form and structure
Is the radiation dose high enough to cause instant death used in diagnostic exams or therapeutic treatments?
No
Do reproductive cells die?
No, they permanently lose its ability to procreate
When does reproductive death result?
From exposure of cells to doses of ionizing radiation in the range of 1-10Gy
What is apoptosis?
Non-mitotic, or non-division form of cell death that occurs when cells die without attempting division during the interphase portion of the cell cycle
What is another name for apoptosis?
Programmed cell death
What is an example of apoptosis?
Human skin cells die, are replenished, and maintain a protective outer coating known as skin
What is mitotic death?
-Occurs when a cell dies after one or more divisions
-Small doses of radiation have the ability to cause this type of cell death
What is mitotic delay?
-Exposing a cell just before it begins to divide
-Failure of the cell to start dividing on time
-After this delay normal mitotic functions can resume
What are radioinsensitive cells?
-Brain cells
-Muscle cells
-Nerve cells
What are radiosensitive cells?
-Basal cells of the skin
-Blood cells such as lymphocytes and erythrocytes
-Intestinal crypt cells
-Reproductive (germ) cells
What enhances the effects of ionizing radiation on biologic tissue by increasing tissue radiosensitivity?
Oxygen
During diagnostic imaging procedures, what human tissues are exposed to x-radiation or gamma radiation?
fully oxygenated
What is the LET for diagnostic exams?
low, very few cells are killed because low doses of radiation are given
What is used sometimes in conjunction with radiation to treat certain types of cancerous tumors?
High-pressure (hyperbaric) oxygen
What does using high-pressure (hyperbaric) oxygen with radiation do?
It increases tumor radiosensitivity
What does the Law of Bergoine and Tribondeau state?
-Immature cells are more radiosensitive than mature ones
-Young tissue and organs are more radiosensitive than older ones
-The higher the metabolism of given cell, the more radiosensitive it will be
-rapidly dividing cells are more sensitive
Why are rapidly dividing cells more radiosensitive?
They are more sensitive because they are more sensitive during mitosis/meiosis
Why is an embryo/fetus more susceptible to radiation damage than a child or adult?
They contain a large number of immature cells
Why do nerve, brain, and muscle cells have a reduced radiosensitivity?
Because people are born with nearly all of these cells; they are nearly immature nor rapidly dividing
What cells are the MOST radiosensitive?
cells undergoing mitosis, blood cells, and gonadal cells
The most mature and specialized in performing functions a cell is, the ______ sensitive it is to radiation.
less
What is hematologic depression?
decreasing number of active cells
