Radiobiology 1 Flashcards
Where does most of the radiation we are affected by come from?
Natural sources (90%) e.g CMBR
What is internal exposure?
Mainly comes from inhalation and mainly radon.
Why weren’t harmful effects of radiation initially noticed?
The effects often take time - latent effects.
What was the first fractionation of raditotherapy?
18 x 1hr treatments to divide concentration of radiation
What is indirect action?
High energy electrons break chemical bonds to release highly reactive chemical agents
What is direct action?
The high energy electron causes damage directly to the cell - notably to the DNA double helix
What does LET stand for and what does it mean?
Linear Energy Transfer
The rate at which energy is deposited along a particle track per unit of distance.
Most of the energy is deposited at the end of the track - the bragg peak
Where does the damage occur following direct or indirect action?
Interactions break DNA strand. (Low LET likely to produce repairable breaks, high LET = multiple strand breaks)
Absorbed Dose is…
the Gy
What is equivalent dose?
This depends on the LET and therefore the type of radiation involved.
Uses a weighting factor which depends upon the quality of radiation.
Equivalent dose = sum of Wr (weighting factor) x D (absorbed dose).
Unit = Sv
What is effective dose?
different organs and tissues experience radiobiological damage differently ( as well as dependence on LET).
Tissue weighting factor is added. E= Wt x Ht
Unit is also Sv
What is a deterministic effect?
The severity of effect - depends on the amount of dose received.
Usually a threshold before an effect is apparent.
e.g erythema
What is a stochastic effect?
Probability of occurrence depends on the amount of dose - not guaranteed.
Never a probability of zero.
e.g cancer induction
What does a therapeutic ratio mean?
High probability of tumour control and tumour cell death while minimising risk to normal tissues.
How is a therapeutic ratio achieved?
Through fractionation.
Through conformation, geometrically and dosimetry, high dose to the target volume to minimise dose to surrounding tisues.
