radiobiology Flashcards
STOCHASTIC EFFECT
A stochastic effect means at random.
Usually the effects can take a long time to appear (years to decades).
The probability of the effect occurring (rather than its severity), increases with dose.
Even minor exposures carry some risk as damage to even a single cell can theoretically result in the production of mutation or disease.
Assumption that there is no minimum safe threshold dose
LATENT PERIOD.
The delay in the effects of radiation
DETERMINISTIC EFFECT
Deterministic radiation responses usually follow high-dose exposures and generally appear in a short time period.
Not random. But are deliberate and known effects.
Deterministic effects are usually associated with high dose radiation levels of exposure resulting in cell mutation or death and/or degenerative changes in the tissues exposed
Interactions of Radiation with Tissue
DIRECT is the result of ionisation or excitation of DNA, RNA or Protein molecules.
DNA is referred to as the target molecule.
DNA is not abundant within the cell (less than 1% of the cell volume).
According to target theory, cell death will only occur if the target molecule is inactivated. i.e. DNA is damaged.
INDIRECT refers to effects as a result of interactions within the surrounding medium e.g. cytoplasm of the cell, which in turn interact with the target molecule (DNA).
The ionisation or excitation of water molecules leads to the creation of FREE RADICALS.
These free radicals are intermediaries which can migrate to the target molecule i.e. DNA and transfer their energy to the DNA resulting in damage.
Free radical induced damage to DNA is the primary cause of biologic damage in low LET radiation.
Because of the high water content of tissues (80%) and DNA being less than 1% of the cell volume, most interactions are INDIRECT.
radio-sensitive cells are
Have a high division rate
Have a high metabolic rate
Are of a non specialised type
Are well nourished
MAIN-CHAIN SCISSION
This is the breakage of the backbone of a molecule or DNA strand. In DNA it can sever one or both side rails of the strand.
CROSS LINKING
When the side rail on a DNA strand is broken, it may slip and cross link
POINT LESSION
A disruption of a single chemical bond which is not detectable but can cause malfunction within the cell.
The Five R’s
REPOPULATION RADIOSENSITIVITY REPAIR REDISTRIBUTION RE-OXYGENATION:
Low Doses
Low doses spread out over long periods of time do not cause an immediate problem to any body organ or the whole body.
High Doses
It is sometimes difficult to understand why some people die while others survive after being exposed to the same radiation dose
Acute Radiation Sickness
When the whole body is subjected to a high acute radiation dose, there are a series of clinical responses known collectively as acute radiation sickness.
ARS is a full body response rather than just an organ or cell response.
ARS is a group of sub-syndromes occurring at different stages over the period of hours to weeks, after exposure.
Manifestation of each of the sub-syndromes occur in a predictable sequence of events.
PRODROMAL
Dose dependent and can begin within minutes to hours after exposure.Symptoms: Anorexia, nausea, vomiting, diarrhoea, increased salivation, abdominal cramps and dehydration
LATENT or ASYMPTOMATIC
The prodromal symptoms subside. Like an incubation period during which the organ system damage is progressing. Stage which may last days to weeks.
MANIFEST ILLNESS
Abrupt onset of moderate to severe symptoms relevant to the underlying organ system damage.
