Radiation Biology Flashcards
This occurs when an X-ray photon ionizes water which results in the production of hydrogen and hydroxyl free radicals
Free radical formation
Uncharted atom or molecule that exists with a single , unpaired electron in its outermost shell ( highly reactive and unstable)
Free radical
To achieve stability , the free radicals may :
> recombine with other free radicals without causing changes in the molecule
combine with other free radicals and cause changes
combine with ordinary molecules to form a toxin (hydrogen peroxide) capable of producing widespread cellular changes
2 theories of radiation injury
Draft theory and indirect theory
Theory where cell damage results when ionizing radiation directly hits critical areas, or targets within the cell
Direct theory
Theory where X-ray photon are absorbed within the cell and cause formation of toxins which in turn damage the cell
Indirect theory
2 classification of biological effects of radiation
Stochastic and deterministic effects
The probability of occurrence increases with the increasing absorbed dose ( cancer and genetic mutation)
Stochastic effects
The severity of the response is proportional to the dose (loss of hair, cataract formation, acute radiation syndrome)
Deterministic effects
2 radiation effects
Somatic and genetic effects
Effects that are seen within minutes, days or weeks after exposure (acute radiation syndrome)
Short term effects
Effects that appear after years, decades or generations (cancers, birth abnormalities)
Long term effects
Effects on radiation seen on the person irradiated (cancer, cataracts)
Somatic effect
Effects not seen on the person irradiated but are passed on to future generations (genetic mutations)
Genetic effects
TRUE or FALSE
Nucleus is more radio sensitive than cytoplasm
True (sensitive site is the DNA within the chromosomes)
TRUE or FALSE
The type of damage depends on the stage of cell in the cell cycle at time of irradiation
True
TRUE or FALSE
Younger the tissue and organ, the more radio resistant
False (radio sensitive )
TRUE or FALSE
When level of metabolic activity increases, the radiosensitivity decreases
False ( also increases)
TRUE or FALSE
As the rate for cells and the growth rate for tissue increases, the radiosensitivity increases
True
TRUE or FALSE
Mature cell is more resistant to radiation
True
Radiation effects on cell kinetics
Mitosis delay, cell death and recovery
Characteristics of most radiosensitive cells
> have high mitotic rate
undergo many future mitoses
most primitive in differentiation
5 categories of radiosensitivity
> vegetative inter mitotic cells - basal cells
differentiating intermitotic cells - spermatocytes
multi potential CT cells - fibroblast
reverting postmitotic cells- parenchymal cells of the liver
fixed postmitotic cells- neurons
Severity of damage depends on the amount of radiation received
Dose
Rate of exposure
Dose rate
Rate of loss of energy from a particle as it moves along its track
Linear energy transfer (LET)
TRUE or FALSE
Greater cell damage occurs in the presence of oxygen
True
2 system used to define radiation measurement
> traditional system ( R, rem, rad)
> systeme Internationale unit (Kerma, sv, gy)
Measurement of ionization in air produced by X-rays
Exposure
Quantity of x- radiation or gamma radiation that produces and electrical charge of 2.58 x 10-4 coulombs in a kilogram of air at standard temperature and pressure conditions
Roentgen
Unit that Measures the kinetic energy from photons to electrons
Kerma
What are the HIGH radiosensitive organs
Lymphoid organ, testis, intestine, mucous membrane, bone marrow
What are the intermediate radiosensitive organs
Growing cartilage and bones, fine vasculature, liver, lungs, kidney and salivary glands
What are the low radiosensitive organs
Optic lens, mature erythrocytes, muscle cells, neurons
Amount of energy absorbed by a tissue
Dose
This is used to compare the biological effects of 2 different types of radiation to a tissue or organ
Dose equivalent measurement
A special unit of dose that is equal to the deposition of 100 ergs if energy per gram of tissues (100 ergs/gm)
Radiation absorbed dose
Sum of the products of absorbed dose average over a tissue or organ and a quality factor (QF) or radiation weighting factor (WR) specific for a type of radiation
Rem
Dimensionless multiplier used to place the exposure effects of different types of radiation on a common scale
Quality factor
This is used to estimate the risk in humans (WT xHT “equivalent dose to each organ or tissue)
Effective dose
Critical organs during dental radiograph exposure
Skin, thyroid glands, eyes, bone marrow
Study of the effects of ionizing radiation on living systems
Radiation biology
