Biological Effects of Ionising Radiation & Risk Assessment Flashcards
Why does radiation cause biological effects ?
Ionises atoms when passing through tissues.
Define direct effect of ionising radiation.
Interaction with DNA directly or important structures of the cell.
Define indirect effect of ionising radiation.
Interaction with water in cell producing free radicals - unstable, highly reactive molecules.
What are the 4 factors which extent of biological effect of ionising radiation depends upon ?
Type of radiation, dosage, dosage rate, cell type irradiated.
What types of cells are most sensitive to ionising radiation ?
Highly mitotic cells i.e. stem cells.
What types of cells are least sensitive to ionising radiation ?
Differentiated cells - show no mitotic behaviour.
Name 3 types of tissues which have high sensitivity to ionising radiation.
Bone marrow, lymphoid, gonads, gastrointestinal, embryonic, thyroid.
Name 3 types of tissues which have moderate sensitivity to ionising radiation.
Skin, lens of eye, vascular endothelium.
Name 3 types of tissues which have low sensitivity to ionising radiation.
CNS, connective tissues, bone and cartilage.
Define dose.
Measure of amount of energy transferred and deposited in medium.
Define absorbed dose. What is it measured in ?
Energy deposited by radiation - measured in Grays.
Define equivalent dose. What is it measured in ?
Absorbed dose x weighting factor - measured in Sv.
What is the weighting factor for beta, gamma and x-rays ?
1
What is the weighting factor for alpha EM radiation ?
20
What is the linear threshold model ?
Estimate of long term biological damage from EM radiation with damage being directly proportional (linear) to dose.
Define response linearity.
Several small exposures = effects as 1 large exposure.
Meaning effective dose is directly proportional to cancer risk.
What is the probability of cancer after intra-oral radiation ?
< 1: 10 million.
What are the two radiation effects.
Deterministic and Stochastic.
When do deterministic effects occur following radiation exposure ?
Within days.
Will only occur above threshold dose.
What are examples of deterministic effects ?
Cataracts and bone marrow RB depletion - 0.3Sv.
Sterility and hair loss - 0.5Sv.
Fatal - >6Sv to whole body.
Define Stochastic effect.
No known threshold dose.
Unpredictable severity.
When will Stochastic effects occur following radiation exposure ?
Years after.
What are the two subdivisions of Stochastic effect ?
Somatic and genetic.
Over what dosage will radiation to abdomen likely void pregnancy ?
> 100mGy.
Over what dosage will radiation to abdomen likely cause growth defects during 2-8 weeks.
> 250mGy.
Can pregnant women receive intra-oral radiation ?
Yes. Risk is negligible as long as X-ray tube is not pointed towards their abdomen.
What distance should controlled area be from xray tube ?
1.5m
What are the 4 practices which can be implemented to enhance optimisation and dose limitation in protection of patients during radiation exposure ?
Use of collimator (rectangular).
60-70kV dose.
E-speed film used as less photons required.
>2000cm focus to skin distance.
What is a diagnostic reference level ?
Give an indication of the expected radiation dose received by an average-sized patient undergoing a given imaging procedure.
