Topic 6: ionizing radiation exposure effects Flashcards
How much does man-made exposure contribute to annual exposure?
14% from all sources
Describe exposure
- Traditional method of measuring amount of ionization in air
- Ratio of total charge produced in volume of air
- Unit Coulombs/kg OR Rontgen
- Only applies to X/gamma rays
Conversion between Rontgen and C/kg
1R = 2.58 × 10−4 C/kg
Describe absorbed dose
- Energy deposited by e- per unit mass
- Unit = Gray
- Microgray = μGy = 1 × 10−6
- Milligray = mGy = 1 × 10−3
- Absorption of 1J of energy in Kg of substance by ionizing radiation
Describe KERMA
- Photon beam + medium = release e- with Kinetic Energy Released into Medium = KERMA
- Unit = J/Kg = Gy
- KERMA dose +absorbed dose different at high energies BUT almost equal at low
What is the difference between KERMA + AD
- KERMA = energy released
- AD = energy absorbed
Describe equivalent dose
- Effect of radiation exposure on human tissue to be determined
- Relates absorbed dose > effective biological damage of radiation
- However not all radiation = biological effect for same AD
- Unit = Sievert
- MicroSievert = μSv = 1 × 10−6
- MilliSievert = mSv = 1 × 10−3
What is the formula for equivalent dose?
𝑯𝑻 = σ𝑹 𝒘𝑹𝑫𝑻,𝑹.
- HT = equivalent dose
- σ𝑹 = sum of all radiation
- wR = radiation weighting factor
- DTR = AD
Describe the WR
- Takes into account some radiations more dangerous than others to biological tissue
- Values change periodically
How to convert dose from Gy to Sv
Multiply by wR
Define dose rate
- Exposure as amount over specific time period
Describe the effective dose
- Probability of harmful effect from exposure depending on organ tissue exposed
- Relates equivalent dose > dose of that organ
- Unit = Sv
What is the formula for effective does?
E= ∑T wT HT
- E = effective dose
- ∑T = sum of all tissues
- wT = tissue weighting factor
- HT = equivalent dose
Describe the molecular effect of ionizing radiation
- Each ionization = cluster of ion pairs = 100 eV
- Even small exposure = millions of ion pairs in tissue
- Energy deposited = very high + localized + non-uniform
- Radiation produces = 70x more energy needed to break H-bonds in DNA
What % of ionizing events are potentially harmful?
1%
Why is only 1% of ionization events harmful?
- Most energy absorption events = not close to important cellular macromolecules
- H2O = most abundant cellular molecule + radiation absorbed ionizes H2O molecules in nanoseconds
- Radiolysis of H2O = OH+/H+ radicals = highly reactive = recombine H2O
What happens if the radicals reform with other biological macromolecules?
- Indirectly initiate subcellular events = produce temporary/permanent changes in cells
- Even small dose = delayed but increased risk of cancer OR genetic change in future generation
- High dose = kill cells + clinical signs of change in tissue function
Which free radical is the more damaging?
- OH+
- Initiates 2/3 of all effects to body of X/gamma rays
Give the effects of radiation exposure on DNA
1) Base modification/deletation
2) Bond breakage
3) Single strand breaks
4) Double strand breaks
5) Cross linkage
Describe base modification
- Causes = genetic defect + increased mutation in reproductive cells
- If not repaired/eliminated = risk of malignant trasformation
Describe bond breakage
- Loss of base +change in molecular shape/structure
Describe single strand breaks
- Occurs random in either strand along double helix
Describe double strand breaks
- Due to single or random 2 single events on complimentary DNA strands
- More probable = higher X-ray + dose rate
Describe cross linkage
- Inhibits replication of DNA
