Chapter 7 Molecular and Cellular Radiation Biology Flashcards
What is Radiation Biology?
branch of biology concerned with effects of ionizing radiations on living systems
What is ionizing Radiation?
knocking of electrons from atoms that make up molecular structures of systems
What are the the two types of ionizing radiation?
electromagnetic radiation - electric and magnetic fields that travel through space at the speed of light
particulate radiation - particles emitted from radioactive decay
What are the two types of electromagnetic radiation?
X-ray - 2nd most energetic type, weighting factor of 1
Gamma - most energetic type, weighting factor of 1
What are the two types of particulate radiation?
Beta - used in radiation therapy weighting factor of 1
Alpha - emitted from plutonium and uranium weighting factor of 20, greatest biologic effect internally
What is Linear Transfer Energy?
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 the unit of measurement for LET?
keV/micrometer
What are the low LET’s and high LETs
Low - Gamma and X-ray
High - alpha and beta
Why do high LET particles lose energy quickly?
more ionization per unit of distance traveled
Where are repair enzymes working at to repair radiation damage?
molecular level
What is Relative biological effectiveness?
capability of radiations with various LETs to produce a particular biologic reaction, various LETs do not render the same biologic effect
How is relative biologic effectiveness quantified
RBE = dose in Gy from 250-kVp X-rays/ dose in Gy of test radiation
What type of tissue is more radiosensitive?
oxygenated is more radiosensitive compared tohypoxic or anoxic
What is the oxygen enhancement ratio?
ratio of radiation dose required to cause particular biologic response in oxygen-deprived environment to the radiation dose required to cause identical response under normal oxygen conditions
What does high LET radiation cause?
biologic effect from direct action
What does low LET radiation cause?
OER about 3.0 with high dose 2 Gy or more, direction action creating free radicals cause more biologic damage with greater oxygenation
What are the three areas that repair can happen?
molecular, cellular, organic
What happens when tissue has a direct action with ionizing radiation?
usually with high LET radiation, when ionizing radiation interacts with DNA RNA proteins or enzymes
What is radiolysis of water?
radiation interacts with water molecules and free radials are produced
What happens with indirect action of ionizing radiation?
free radicals produced with radiolysis/hydrolysis
What are the different effects of ionizing radiation on DNA?
single string break
double strand break
chromosome effect after double strand break in same rung of DNA
mutation
covalent cross link
What are the effects of ionizing radiation on chromosomes?
radiation induced chromosome breaks
chromosomal fragments
chromosomal anomalies
What is the Target Theory?
concept of radiation damage resulting from discrete and random events, master or key molecule is necessary for the survival of the cell, used to explain cell death and nonfatal cell abnormalities caused by exposure to radiation
What are the effects of irradiation on the entire cell?
instant death - 1000 Gy in less than a few minutes
reproductive death - 1-10 Gy, cannot procreate
apoptosis - non mitotic cell death that occurs when cells die without attempting division in interphase, caused by a few hundred cGy
mitotic death - less dose than apoptosis, cell dies after one or more divisions
mitotic delay - 0.01 Gy can cause, may or may not resume normal function
What are the two types of cells?
mature and immature
What are mature cells?
more specialized in function, divide at a slower rate or do not divide at all, not as sensitive to radiation, highly differentiated
What are immature cells?
nonspecialized, undergo rapid cell division, more sensitive to radiation, undifferentiated, lymphocytes most sensitive
What are oxygen enhancement effects?
enhanced effects of ionizing radiation, increased radiosensitivity, more free radicals are formed, high is x-ray and gamma because they are indirect
What does radiation therapy have to do with oxygen enhancement effects?
high pressure O2 is used to increase radio sensitivity of some types of tumors
What is OER?
ratio of radiation dose required to cause a particular biologic response
What is the number of OER for x-ray and Gamma?
3
What is the Law of Bergonie and Tribondeau
radiosensitivity of cells are directly proportional to their reproductive activity and inversely proportional to their degree of differentiation, most radiosensitive cells are least specialized, least mature, have greatest reproductive capability, and longest mitotic phase, originally only applied to germ cells but now true for all cells of the body
How are blood cells effected from ionizing radiation?
lymphocytes most radiosensitive
How are epithelial tissues effected from ionizing radiation?
body constantly regenerates, very radiosensitive including lungs intestinal lining, blood and lymphatic vessel lining
How are muscle tissues effected from ionizing radiation?
highly specialized, radio resistant
How are nervous tissue effected from ionizing radiation?
highly specialized in adults, radioresistant, fetus 8-15 weeks most radiosensitive
How are reproductive cells effected from ionizing radiation?
germ cells are radiosensitive
How much Gy can cause temporary sterility?
2 Gy
How much Gy can cause permanent sterility?
5-6 Gy
