Week 6 - Molecular & Cell Biology Flashcards
What is radiation biology?
A branch of science concerned with effects of ionizing radiation on living systems
What does radiation biology include?
- Sequence of events occurring after the absorption of energy from ionizing radiation
- Action of living systems to make up for the consequences of this energy assimilation
- Injury to the living system that may be produced
What are the information sources for Radiation biology?
- Animal and plant experiments
- Observation of humans who have been exposed to radiation under known circumstances
What are the effects of ionizing radiation?
Damages living systems by ionizing atoms comprising the molecular structure of these systems
What does biologic damage begin with?
The ionization produced by various types of radiation such as x-rays, gamma rays, alpha particles, beta particles and protons
What are 3 important concepts to help us understand the way ionizing radiation causes injury?
- Linear energy transfer (LET)
- Relative biologic effectiveness (RBE)
- Oxygen enhancement ratio (OER)
What is LET?
The average energy deposited per unit length of track by ionizing radiation as it passes through and interacts with a medium along its path
What is LET measured in?
keV/um
What is high LET?
More damaging and less penetrating
What are examples of High LET?
Alpha particles
What is low LET?
Less damaging but more penetrating
What are examples of low LET?
X-ray and gamma rays
What is RBE?
The relative capability of radiation with differing LETs to produce a particular reaction
What is the formula to calculate RBE?
RBE = Dose in Gyt from 250-kvp rays/Dose in Gyt of test radiation
What is the RBE of xray and gamma rays?
Approximately 1
What is the RBE for alpha radiation?
Approximately 3
What also affects RBE?
The manner in which the dose is delivered
What is the general rule for radiation delivered over a long period of time?
Radiation delivered over a long period of time will be less effective
What is the reason radiation delivered over long periods of time are less effective?
Some cell will recover from the damage as time passes
What are the two ways in which ionizing radiation can be stretched?
- Fractionation
- Protraction
What is Fractionation?
Radiation therapy where a total dose is divided into multiple sessions
What is protraction?
A continuous dose delivered at a low rate
What is OER?
The ratio of the radiation dose required to cause a particular biologic response of cell in an oxygen deprived environment to the radiation dose required to cause an identical response under normal oxygenated conditions
What is the OER of x-rays and gamma rays?
3.0 when radiation dose is high
When could OER be less?
When radiation dose is below 2 Gyt
What is the OER formula?
OER = Radiation dose without O2/Radiation dose with O2
At what 3 levels can biologic damage resulting from exposure be observed in?
- molecular
- cellular
- organic
Where do any visible radiation-induced injuries of living systems always begin?
At the molecular level
What does molecular damage result in?
The formation of structurally changed molecules that may impair cellular function
