Week 5: Biological effects of radiation (part 1) Flashcards
What are the two important molecular effects?
Direct damage to molecules.
Generation of high-active chemicals (free radicals) leading to additional biomolecular damage.
What are free radicals and what causes them?
Primary radiation causes the ionisation of simple molecules, creating free radicals.
Free radicals are neutral atoms or molecules with an unpaired electron.
Why are free radicals dangerous?
They are extremely chemically reactive, and can be electron acceptors (oxidisers) or donors (reducing agents).
Free radicals diffuse and induce chemical changes in critical biological structures, which is the main form of overall damage as a result of radiation exposure.
What is the definition of activity? What are its units?
The activity of a radioactive source is the rate at which its atoms decay.
It is measured in becquerels (Bq), which are defined as one disintegration per second.
What is linear energy transfer?
LET measures the energy deposited along the at travelled, typically expressed in the units keV um^-1.
It is very similar to the stopping power seen previously, but is used in the biological context.
What types of radiation have low LET?
Fast electrons.
Gamma rays.
X-rays.
What types of radiation have high LET?
Heavy charged particles.
Fast neutrons (due to scattering off nuclei).
What is the biological difference between high and low LET.
High LET radiation produces more irreparable damage than the same dose delivered by low LET radiation.
What is absorbed dose? How is it calculated? What is its unit?
Absorbed dose D measures the amount of radiation energy eT deposited in a mass mT of tissue or organ.
D = eT/mT
The unit of absorbed dose is the gray (Gy), which is equal to 1 Jkg^-1.
What is equivalent dose?
The equivalent dose H includes the relative radiation weighting factor wR for different types of radiation.
For a tissue or organ T, irradiated by radiation R to an absorbed dose D(TR), the equivalent dose is:
H(T) = w(R) D(TR)
The unit of equivalent dose is the Sievert (Sv).
List the typical radiation weighting factors for different radiation.
Photons - 1
Electrons and muons - 1
Protons and charged pions - 2
Alpha, fission fragments, heavy ions - 20
Neutrons - f(E)
How is the equivalent dose from a mixed radiation field calculated?
If different types of radiation are present, the equivalent dose is equal to the sum of the equivalent doses from the individual types of radiation.
(30)
What is the effective dose?
The effective dose E recognises that some organs are more radiosensitive than others.
To account for this, they are given a tissue weighting factor wT.
The effective dose is the sum of the equivalent doses to the organs, weighted by the appropriate factors.
(31)
What is the effective dose for a whole body?
The effective dose will be equal to the equivalent dose.
List the tissue weighting factors.
Bone-marrow (red), colon, lung, stomach, breast, remainder tissues:
wT = 0.12 sum(wT) = 0.72
Gonads:
wT = 0.08 sum(wT) = 0.08
Bladder, oesophagus, liver, thyroid:
wT = 0.04 sum(wT) = 0.16
Bone surface, brain, salivary glands, skin:
wT = 0.01 sum(wT0 = 0.04
Total sum(wT) = 1.00
Give four examples of possible biological consequences from exposure to radiation.
Cell death
Cancer
Genetic defects
Death
State the definition of linear energy transfer and give the typical units used for this value.
The energy deposited per unit length travelled.
kV um^-1
