Biological effects of radiation Flashcards
3 types of interactions of electrons with matter
- Ionisation
- Excitation
- Heat production
Describe the folling interaction process of electron with matter:
IONISATION
- Electrons produced via PE, PP, compton
- Photoelectrons loose 34eV for each ionisation caused
- 100keV photoelectron = 3000 interactions
Describe the folling interaction process of electron with matter:
EXCITATION
- Incident electron raises orbital electron to higher energy orbit without ejection
- change in chemistry
- returns to original state with emission of low energy photon
Describe the folling interaction process of electron with matter:
HEAT PRODUCTION
- Incident electron gices energy to whole atom
- increase in KE -> heat
Describe electron range in air graph
Relatively constant ionisation until they reach their range and deposit all their energy in one go.
7 effects of radiation
give example for each
- Heating effects - Calorimetry
- Ionization - ion chambers
- Light production on irradiation - thermiluminescence
- Physico-chemical effects - photographic film
- Chemical changes - iron from 2+ to 3+ when UV hits
- Biochemical changes - Enzyme activation
- Biological changes - Kill cells/bacteria
Which cells are most suvvecptible to radiation damage?
Why?
Give examples
Cells that divide more rapidly have greater radiosensitivity
e.g. lymphoma cells, heampetic stem cells
Radiation damage mechanism:
Ionisation
- Ionised atom has net positive charge and is chemically reactive
- Ionisation of water is important
- Damage to DNA is most significant
Radiation damage mechanism:
Radiolysis of water
How does this provide evidence of DNA damage?
- Radiation + H20 = H20+ + e-
- H20+ = H+ + OH.
- e- + H20 = H20-
- H20- = H<strong>.</strong> + OH-
Two ways of making free radiacals. The Hydroxyl radical is highly reactive because of it’s unpaired electron. Can go on to make toxic Hydrogen peroxide. EVIDENCE that OH radical is involved in producing DNA single strand breaks, chromosome aberation, bacterial and mammalian cell killing.
Two types of action on DNA
Which is most likely at diagnostic energies?
- Direct - initial x-ray interactions
- Indirect - arising from free radiacal interactions
Indirect is more likely at diagnostic energies.
1Gy of x-ray radiation causes how many:
SSBs
DSBs
SSB - 1000
DSB - 100
What is Linear Energy Transfer?
unit?
How does LET depend on beam penetration power?
LET is a measure of the rate at which energy is transferred to the medium (i.e. ionization density along the track of the particle)
keV/um
More penetrating beam = lower LET
Describe the radiation effects following a large whole body dose (4.5Gy)
0-48 h
48h - 2weeks
3 weeks - 4 weeks
> 4 weeks
- 0-48 h
- What: Lause of appetite, nausea, sweating, fatigue
- Why: Tocic chemicals from free radicals
- 48h - 2weeks
- Apparent recovery
- Differentiated cells are relatively radioresistant
- 3 weeks - 4 weeks
- Loss of hair, infection, heamorrhage
- Replacement stem cells severly depleted
- > 4 weeks
- Gradual recover or death
Effects of
10 – 100 Gy
100 – 150 Gy
150 Gy
- 10 – 100 Gy
- Damage to intestinal stem cells, loss of water and body salts to gut. Death in 3-4 days
- 100 – 150 Gy
- CNS disturbances
- 150 Gy
- Loss of lung function
How dp you describe the biological effects of different ionizing radiations?
Relative Biological effectiveness (RBE)
RBE = dose of 200kVp x-rays / dose of other radiation to give same biological effect
