QUIZ 5 RADIATION PHYSICS
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Created by:
kj2013kj on September 25, 2012
Subjects:
FUNDAMENTAL PRINCIPLES OF RADIOBIOLOBY
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70 terms
Terms | Definitions |
|---|---|
 What is the fundamental principle of radiobiology | relates a dose of radiation to what happens in body |
| what is the law of Bergonie and Tribondeau | radiosensitivity of tissue varies with maturation and metabolism |
| when are cells the most radiosensitivie | in utero |
| which are the most radiosensitive cells | stem cells, young tissue, increased metabolic rate, increased proliferation and growth rate |
| which are the most radioresistant | mature cells, older tissue, decreased metabolic rate |
| what are the physical factors affecting radiosensitivity | LET, RBE, protraction and fractionation |
| what is LET | linear energy transfer |
| describe LET | rate at which energy is transferred to soft tissues per unit length (track length) |
| what is track length on LET | how far photon goes into tissue |
| what is measurement of LET | kiloelectronvolt / micrometer |
| what is diagnostic xray LET | 3 kiloelectron volt / micrometer |
| what is radiation therapy LET usually | 250 kiloelectron volt / micrometer |
| what is LET useful in describing | quality of radiation |
| how do you describe quality of radiation | LET |
| what is the quality of radiation | size + charge |
| what radiation is low LET | EMR which is X-ray and gamma rays |
| what type of radiation quality is low LET | high energy but small particles |
| how does low LET cause tissue damage | indirect action, tissue brakes photon with absorption and attenuation |
| ... | photon hits water then free radicals hit DNA |
| what type of DNA damage does low LET cause | causes single strand break of one base pair |
| what type of radiation is high LET | alpha particles, radiation that has substantial mass and charge |
| what type of track does high LET have | doesn't travel far due to mass, like a bowling ball |
| what type of track does high LET have | has dense ionization, energy is exhausted in a short length of track |
| what type of DNA damage does high LET cause | double strand break |
| what is RBE | relative biologic effectiveness |
| describe RBE | the capability of radiation with varying LET to produce a biologic response |
| how does LET affect RBE | as LET increases, RBE increases |
| what is RBE of diagnostic x-rays | 1 |
| how do you calculate RBE | dose of standard radiation to produce given effect Gamma divided by the dose or standard radiation to produce given effect Alpha |
| how do you calculate RBE | dose of standard radiation to produce effect of gamma divided by alpha |
| How is radiation therapy delivered | protraction and fractionation |
| why use protraction and fractionation in radiation therapy | to allow for intracellular repair, tissue recover and higher total doses |
| how is protracted treatment delivered | lower dose delivered continuously over long perior or time |
| how is fractionated treatment delivered | dose delivered in equal portions at regular intervals |
| how do biologic factors affect radiosensitivity | alters tissue response to radiation |
| what are the biologic factors affecting radiosensitivity | oxygen effect, age, recovery, chemical agent, hormesis |
| what is oxygen effect | tissues high in oxygen are more sensitive to radiation |
| what is oxygenation enhancement ratio OER | ratio of dose required to produce a particular biologic response in a hypoxic environment divided |
| what is oxygenation enhancement ratio OER | dose required to cause some response in oxygenated environment |
| what is OER of diagnostic x-rays | 3.0 |
| what is the biologic factor of age | humans are more radiosensitive in utero, decreasing with age until elderly |
| what is the recovery biologic factor | cells can recover from sublethal radiation damage |
| what is the recovery biologic factor | but if dose kills cell before next division, interphase death occurs |
| what is the recovery biologic factor | cells cannot recover from interphase death |
| what is recovery | intracellular repair + repopulation = recovery |
| how do chemical factors affect radiosensitivity | some chemicals can modify the radiation response |
| how do chemical factors affect radiosensitivity | radiosensitizers increase effects of raidation, called halogenated pyramidines |
| how do chemical factors affect radiosensitivity | radioprotectors decrease effects of radiation, call cysteine, but these are fatal |
| what is hormesis | possible beneficial effect of a small amount of radiation |
| how does hormesis work | stimulates hormonal and immune responses and extends life span |
| what is radiation dose-response relationship | relationship between radiation dose levels and the response observed |
| how are radiation dose-response relationships demonstrated | graphically through a line or curve |
| what types of graphs are there | linear, non linear, threshold, non threshold |
| what is linear radiation dose response relationship | response is directly proportional to dose in straight line |
| what is non threshold radiation dose relationship | regardless of size of dose it is expected to produce a response |
| what are dose limits based on | linear non threshold relationships |
| what type radiation dose relationship is radiation induced genetic damage and late effects | linear non threshold |
| how are low dose results obtained from high dose results | extrapolated |
| varied doses produce varied responses and are called | non linear |
| what is threshold radiation dose relationship | dose is larger than 0, the level below which there is no response |
| what can have a sigmoid curve and a sigmoid curve can only occur in | non linear threshold response |
| when would you see sigmoid curve | radiation therapy to show high dose cellular response |
| what is Gray | amount of radiation required to deposit one joule of energy in 1 kg of any kind of matter |
| what is dose to patient measured in | Rad or Gray, 1 Gray = 100 rads |
| what is Gyf | absorbed dose to patient |
| what is radiation dose to tech measured in | Rem or Sievert. 1 sievert = 100 rem |
| describe Sievert | the dose to tech of a given type of radiation in Gray that has same effect on human as 1 Gray of X-ray or gamma radiation |
| How is radiation in air meaused | Roentgen, or coulombs per kg or air kerma, or gray in air, 1 gray in air = 100 roentgens |
| what is the relationship between OER and LET | The relationship between the oxygen enhancement ration (O.E.R.) and the linear energy transfer (L.E.T.) is that the OER is LET-dependent. The O.E.R. is highest for low-L.E.T. radiation and decreases in value as the L.E.T. increases |
| Radiation Weighting Factor | Radiation Weighting Factor a) The radiation weighting (Wt) factor is the factor by which the absorbed dose (rad or gray) must be multiplied to obtain a quantity that expresses, on a common scale for all ionizing radiation, the biological damage (rem or Sievert) to the exposed tissue. It is used because some types of radiation, such as alpha particles, are more biologically damaging to live tissue than other types of radiation when the absorbed dose from both is equal. This replaces the term quality factor in the latest system of recommendations for radiation protection. For example, the gonads have a Wt of 0.20; whereas the skin has a Wt of 0.01 as the gonads are more sensitive to radiation than the skin. |
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