Week 2 Radiobiology Flashcards
Radiobiology
the study of the action of ionizing radiation on living things
Bergonie and Tribondeau, 1906
any cells that are immature, undifferentiated and actively dividing (i.e., stomach mucosa, basal layer of skin, stem cells) are more radiosensitive
Cells that are mature, differentiated and not actively dividing (i.e., neurons) are more radioresistant
Types of ionizing radiation
Electromagnetic
X-rays
produced in an electrical device that accelerates electron to high energy and abruptly stops them in a target (tungsten or gold)
Gamma rays
Emitted by radioactive isotopes
Types of ionizing radiation
Particulate
Electrons Protons α-particles Neutrons Heavy charged particles
Absorption of x-rays
Directly Ionization
Disrupt the atomic structure, producing chemical and biologic changes
α particles, protons
electrons, β-, β+
High LET radiation
Absorption of x-rays
Indirect ionization
Give up energy to charged particles, which are able to produce damage.
Neutrons
EM Radiation
Interact with other atoms or molecules to produce free radicals
Mitosis
process of cell division that results in two genetically identical daughter cells developing from a single parent cell.
Cell cycle
There are 4 phases of mitosis:
M Phase, in which cells divide in 2
most radiosensitive
G1Phase (gap one), in which cells prepare for DNA replication
S Phase, in which DNA doubles by replication
G2Phase (gap two), in which cells prepare for mitosis
Undifferentiated cells
are precursor or stem cells and have less specialized functions. Their major role is to reproduce to replace themselves and to provide cells which mature into more differentiated cells.
Examples: bone marrow cells, intestinal crypt cells and basal cells of the skin
The more specialized a cells function is, the more differentiated it is
examples are the major organ cells, muscle and neurons
Highly differentiated cell usually have less reproductive activity than undifferentiated cells
radiosensitivity
The most radio-sensitive cells are those which: have a high division rate have a high metabolic rate are of a non-specialized type are well nourished
Single Target-Single Hit
Only one target in the cell associated with cell death and a singal hit on this target is adequate to inactivate the target (viruses and some bacteria)
Multiple-Target Single Hit
Multiple targets per cell, a single hit of any of these targets is required for cell death. Not all targets are hit, some of them are killed, while others are damaged by low doses (sublethal damage) Cells with SLD may repair themselves during interfractional periods
This is valid for mammalian cells
Linear energy transfer (LET)
LET → loss of energy per unit tract length
A function of the charge and velocity of the ionizing radiation
increases as the charge on the ionizing radiation increases and its velocity decreases
Relative biological effectiveness (RBE)
The RBE is the ratio of the 250 kV X-ray dose that produces a specific biological effect to the test dose of any radiation that produces the same effect. The RBE is related to the LET.
High LET (pariculate)
deposits more energy per unit length, more destructive
than same dose of external beam rad.
Alpha particles are slow and positively charged
Beta particle fast and negatively charged
LET alpha>LET beta
RBE-Radiobiologic Effect
RBE=250 kV x-ray dose required for a specific effect/Tested dose of any radiation required for a specific event
Cell survival curves
Relationship between dose and proportion of cells that survive
Linear Quadratic Model
Respones at low levels of radiation are linear, while higher doses are quadratic No threshold (although may be inaccurate at 7Gy+)
