Radiation Biology Flashcards
Discovery of X-ray Tube
Roentgen 1895
Discovery of Radioactivity
Becquerel 1896
Radiation LD-50
5,000 mSv
Hiroshima survivors
63%
Nagasaki survivors
73%
Risk of dying from cancer without added radiation exposure
27.1%
Radiation level at which Cell killing starts:
1,000 Sv
Photoelectric effect
up to 50 keV. photon knocks out photoelectron
Compton effect
60 keV to 2 MeV. photon hits electron, releases compton electron and scatter photon
Pair formation
5 MeV and higher. photon interacts with nucleus to produce electron and positron
eV to make an ion pair
34 eV per ion pair
Linear Energy Transfer
energy per unit path length
usually earliest cancer following high dose of radiation
leukemia
5 mSv equates to what excess lifetime cancer risk?
0.025%
20 mSv equates to what excess lifetime cancer risk?
0.100%
50 mSv equates to what excess lifetime cancer risk?
0.25%
500 mSv equates to what excess lifetime cancer risk?
2.5%
5,000 mSv equates to what excess lifetime cancer risk?
25%
Relative Biological Effectiveness (RBE)
Factor to compare radiation types.
RBE equation
Dose(reference)/Dose(test) - inverse ratio of absorbed radiation required to produce given effect to a standard
Direct effect of Ionizing Radiation
ionization, excitation
Indirect effects
free radical generation
Product of radiolysis of water
hydroxyl free radical
G-Value
# of molecules formed per 100 eV of radiation (efficiency of production of a particular product)
Oxygen effect
Cells in anoxic conditions are less sensitive to ionizing radiation. Free oxygen binds to ionized sites, “fixing” it so can not re-bind with hydrogen
Oxygen Enhancement Ratio (OER)
Radiation dose required to inactivate cell population in absence of oxygen vs with oxygen
Types of DNA damage
Base, Sugar, SS, DS, Base-free sites, Alkali-labile, DNA-protein cross link
Bragg peak
point of highest energy deposition. energy drops off immediately after
unstable chromosome abberations
dicentrics
rings
large deletions
stable (viable) chromosome abberations
balanced translocations
inversions
small deletions
Cerebrovascular syndrome
> 20 Gy, dead in 24-48 hours
Gastrointestinal Syndrome
5 - 20 Gy. Death in 5-10 days
Hematopoetic syndrome
2.5-5 Gy. Symptoms 3-4 weeks later.
Efficacy for Bone Marrow transplant
8-10 Gy only
Treatments to improve LD50
antibiotics
bone marrow transplant
platelet infusion
Dose to fetus (after >16 weeks) of no concern
0.05 Gy
pre-implantation time and effects
0-9 days; lethal effects
organogenesis time and effects
10 days - 6 weeks; malformations
fetal period time and effects
6 weeks to term; growth retardation
Report of Ionizing Exposure to population of the US
NCRP report 160
CT and Nuclear Medicine % increase to exposure
600% increase
absolute risk
disease incidence in a population
250 people / 100,000 population
relative risk
absolute risk in unexposed population relative to exposed population
250 cases/100,000 (exposed)
_______________________
50 cases/100,000(unexposed
odds ratio
odds of diseased person having been exposed relative to non-diseased person
Exposed and diseased/not exposed and diseased / exposed not-diseased/not exposed and non-diseased
type of study for odds ratio
case control study
Excess Relative Risk
Relative Risk - 1
When do you use Odds Ratios
- Cases are representative of all people with disease from the population
- controls are representative
- infrequent disease
Ecological Studies
People are studied as a group i.e. at population level
Ecological Fallacy
infer association b/w disease and exposure for individuals based on their group association
