RAD PHYSICS CH 7 EXAM

LINEAR ENERGY TRANSFER (LET)

LET is the average energy deposited per unit length of track by ionizing radiation as it passes through and interacts with a medium along its path.

LET Units

LET is described in unites of keV per micron. 1 micron (um) = 10-6 m.

LET Value

The LET value of the radiation involved is a significant factor in assessing potential tissue and organ damage from exposure to that type of ionizing radiation.

Low-LET Radiation

Low LET radiation like x-rays and gamma rays, doses that are not excessive primarily cause indirect damage to biological tissues that usually can be reversed by repair enzymes.

High-LET Radiation

High LET radiation like alpha particles, ions of heavy nuclei, and low energy neutrons; can produce irreparable damage to DNA because of inducing multiple strand breaks that cannot be undone by repair enzymes.

RELATIVE BIOLOGICAL EFFECTIVENESS (RBE)

RBE of the type of radiation being used is the ratio of the dose of a reference radiation (conventionally 250 Kvp X-rays) to the dose of radiation of the type in question that is necessary to produce the same biological reaction in a given experiment. The response is what is provided by a dose of test radiation delivered under the same condition.

RBE Concept

The concept of RBE is not practical for specifying radiation protection dose levels in humans. Therefore, to overcome this limitation, a radiation weighting factor (WR) is used to calculate the equivalent dose (EqD) to determine the ability of a dose of any type of ionizing radiation to cause biological damage.

OXYGEN ENHANCEMENT RATIO (OER)

OER is a comparative measure used to obtain the amount of cellular injury for a species of ionizing radiation under poorly oxygenated conditions. Specifically, OER is the ratio of the radiation dose required to cause a particular biological response of cells or organisms in an oxygen deprived environment to the radiation dose required to generate an identical response under normal oxygenated conditions.

Radiation induced biological damage

Radiation induced biological damaged in living systems is observed on a molecular, cellular, and organic systems level.

Radiation Action

Radiation action on the cell is either direct or indirect, depending on the site of interaction.

Sufficient Quantities

If sufficient quantities of somatic cells are affected by exposure to ionizing radiation, entire body by processes can be disrupted. Conversely, if radiation damages the germ cell, the damage may be passed on to future generations in the form of genetic mutations.

Direct Action

Action is direct when biologic damage occurs as a result of the ionization of atoms on essential molecules ( e.g., DNA, RNA, proteins, enzymes) produced by straight interaction with incident radiation.

Indirect Action

Action is indirect when effects are produced are produced by free radicals created by the interaction of radiation with water molecules; these unstable, highly reactive chemical combinations can cause substantial disruption to vital macromolecules such as DNA and result in cell death.

Indirect Action and The Human Body

Because the human body is 80% water and less than 1% DNA, virtually all effects of low-LET irradiation in living cells result from indirect action.

Point Lesions

Point lesions commonly occur with low-LET radiation and are often reversible through the action of repair enzymes.

Double Strand Breaks

Double strand breaks of DNA happen more commonly with densely ionizing (high-LET) radiation and often are associated with the loss of one or more nitrogenous bases. The chance of repair from this type of damage is very low; the possibility of a lethal alteration of nitrogenous bases within the genetic sequence is far greater.

Muscle Tissue

Muscle tissue is relatively insensitive to radiation.

Epithelial Tissue

Because the body continually regenerates epithelial tissue, the cells compromising this tissue are highly radiosensitive.

Lymphocytes

Lymphocytes are the most radiosensitive blood cells, and when they are damaged the body loses its natural ability to combat infection and becomes more susceptible to bacterial and viral antigens.

Embryo-Fetus

The embryo-fetus is very susceptible to radiation damage, which can cause central nervous system (CNA) anomalies, microcephaly, and intellectual disability.

Law of Bergonie and Tribondeau

The Law of Bergonie and Tribondeau states that the most pronounced radiation effects occur in cells with the least maturity and specialization or differentiation, the greatest reproductive activity, and the longest mitosis phases.

Human Germ Cells

Human germ cells are relatively radiosensitive, although the exact responses of male and female germ cells to ionizing radiation differ because their courses of development from immature to mature status differ.

Sterilization in Humans

For both males and females, temporary sterilization occurs at 2 Gyt, and permanent sterilization occurs at 5-6 Gyt.

Developing Nerve Cells

Developing nerve cells in the embryo-fetus are more radiosensitive than are the mature nerve cells of the adult. Studies indicate that the eighth to the fifteenth week after gestation is the time frame for maximal radiosensitivity. A lower but still significant level of risk remains until the 25th week after gestation.

Nerve Cells

Nerve cells in the adult are highly specialized. If the cell of the nucleus has been damaged but not destroyed by exposure to radiation, the damaged nerve cell may still be able to function but in an impaired fashion. Radiation can cause temporary or permanent damage to a nerve’s processes, thus disrupting communication with and control of some body functions.

Cell Survival Curve

The cell survival curve is used to display the radiosensitivity of a particular type of cell, which helps determine the types of cancer cells that will respond to radiation therapy.

Cell Nucleus Damage

When a cell nucleus is significantly damaged by exposure to ionizing radiation, the cell can die or experience reproductive death, apoptosis, mitotic death, mitotic delay, or interference with function.

Target Theory

The target theory states that when a vital macromolecule or target such as cell DNA is directly or indirectly inactivated by exposure to radiation, the cell will die.

Consequences to the Cell

Consequences to the cell from structural changes within the nucleus can result in restitution, deletion, broken-end arrangement with or without visible damage to the chromatids.

Chromosome Abberations

Chromosome abberations and chromatid abberations are two types of chromosome anomalies that have been observed at metaphase.

Genetic Information to Future Generations and Mutation

Because of the genetic information to be passed on to future generations is contained in the strict sequence of nitrogenous bases, the loss or change of a base in the DNA chain represents a mutation.

Interaction on same DNA Rung

When two interactions, one on each of the two sugar phosphate chains, occur within the same rung of the DNA ladder like configuration, the result is a cleaved or broken chromosome, with each new portion containing an unequal amount of genetic material.

Damaged Chromosome Division

When a damaged chromosome divides, each new daughter cell will receive an incorrect amount of genetic material, resulting in either death or impaired functioning of the new daughter cell.

In human beings, how many genes are contained in all 46 chromosomes?

Approximately 30,000

Interphase consists of which of the following phases?

G1, S, and G2

To carry genetic information from the cell nucleus to ribosomes located in the cytoplasm, DNA regulates cellular activity indirectly by reproducing itself in the form of:

mRNA

Which of the following is a process of reduction cell division?

Meiosis

Cytosine bonds only with which of the following nitrogenous organic bases?

Guanine

The process of locating and identifying the genes in the human genome is called:

Mapping

The S phase of mitosis is the:

Actual DNA synthesis period

When a cell divides, the genetic-containing material contracts into tiny rod-shaped bodies called:

Chromosomes

Nitrogenous base pairs form the:

Steps, or rungs, of the DNA ladderlike structure

When somatic cells divide, they undergo:

Mitosis

(T/F) A normal human being has 46 different chromosomes (23 pairs) in each somatic cell.

True

(T/F) Genes control the formation of proteins in every cell through the intricate process of genetic coding.

True

(T/F) Messenger RNA (mRNA) transfers its genetic code to another kind of RNA molecule, called transfer RNA (tRNA).

True

(T/F) Radiation induced damage to chromosomes may be evaluated during telophase.

False

(T/F) Cells are the basic units of all living matter, but they are not essential for life.

False

(T/F) Proper cell function enable the body to maintain homeostasis.

True

Human Genome

The total amount of genetic material (DNA) contained within the chromosomes of a human being.

Cytosine and Thymine

Compounds called pyrimidines

Cell Division

Multiplication process whereby one cell divides to form two or more cells.

Anaphase

The phase of mitosis during which two chromatids repel each other and migrate along the mitotic spindle to opposite sides of the cell.

Genes

Segments of DNA that serve as the basic units of heredity.

Adenine and Guanine

Compounds called purines

Deoxyribose

A 5-carbon sugar molecule

Interphase

The period of cell growth that occurs before actual cell division.

Nucleic Acid

Large, complex macromolecules made up of nucleotides.