Biological Effects of Ionising Radiation

Question 1

What can ionizing radiation be divided into

Answer 1

bi products of radioactive decay

artificially produced electromagnetic radiation

Question 2

What are byproducts of radioactive decay split into

Answer 2

§ Alpha particle
§ Beta particle
§ Gamma rays (ER) (identical to x rays but source is diff)

Question 3

What is the result of ionization

Answer 3

Result of ionisation is a free electron and a positively charged atom

Question 4

What is the effect of ionizing radiation on the body

Answer 4

• Ionising radiation can disrupt structural organic molecules and cells of building elements of our body and the DNA in the cell nucleus

Question 5

Where can evidence of DNA damage be seen

Answer 5

in faulty repair of chromosome breaks leading to development of abnormal cell populations and the development of cancer

Question 6

What is seen in individuals exposed to large doses of radiation

Answer 6

• Faulty repair of breaks is seen in individuals who are exposed to large radiation doses
  
  • Majority of damage is easily repaired depending on category of damage

Question 7

What is the direct effect of radiation

Answer 7

○ Direct effect - radiation interacts directly with the atoms of a DNA molecules or another important part of a cell

Question 8

What is the indirect effect of radiation

Answer 8

○ indirect effect - radiation interacts with water in the cell. When water molecules becomes ionised a highly reactive free radical ion is formed, two of these can combine to form a hydroxyl radical which can diffuse short distances and cause DNA damage

Question 9

What is the advantage of DNA being double helix

Answer 9

advantage of this is that if only one strand of the helix breaks the DNA is held in place by the other strand so is easily fixed

Question 10

What happens if both strands of double helix break

Answer 10

it becomes far more difficult to piece the DNA back together and the two remaining ends will seek to re-join with other free ends, not necessarily the correct matching en

Question 11

What happens if the repair isn’t done properly

Answer 11

can lead to mutations which can affect cell function

Question 12

What does the biological effect depend on

Answer 12

○ Type of radiation
○ Amount of radiaiton / dose
○ Time over which dose is received / dose rate
○ Type of tissue irradiated

Question 13

What is the radiosensitivtiy of tissues depend on

Answer 13

○ The function of the cells that make up the tissues

If cells are actively dividing

Question 14

What are stem cells

Answer 14

exist to produce cells for another cell population
○ Divide frequently
Very radiosensitive

Question 15

What are differentiated cells

Answer 15

○ Do not exhibit mitotic (dividing) behaviour

○ Less sensitive to radiation damage

Question 16

What are highly radiosensitive tissue

Answer 16

○ Skin, vascular endothelium, lung, lens of the eye

Question 17

What are the least radiosensitive tissues

Answer 17

○ CNS, bone and cartilage and connective tissue

Question 18

What does the tissue weight factor do

Answer 18

decide the most sensitive tissues

• Bone marrow colon etc have higher tissue weighting factors compared to other tissues

Question 19

What are the several possible outcomes after radiation hits a cell nucleus

Answer 19

○ No change
		○ DNA mutation 
			§ Mutation repaired
				□ Viable cell 
			§ Cell death 
				□ Unviable cell 
			§ Cell survives but is mutated
				□ Cancer

Question 20

What is absorbed dose

Answer 20

○ Can be measured
○ Measures energy deposited by radiation
○ For intra oral x ray the typical entrance skin dose at the collimator tip is around 2 mgy

Question 21

What is equivalent dose

Answer 21

○ We have seen that diff types of radiation can cause diff levels of damage to tissue
○ Equivalent dose is the absorbed dose multiplied by radiation weighting factors depending on the type of radiation
○ For beta, gamma and X-rays the weighting factor is 1
○ For alpha particles it is 20

Question 22

What is effective dose

Answer 22

○ Represents sarcastic health risk to whole body

Question 23

What is the risk of cancer from intra oral x ray

Answer 23

1 in 10 mil

Question 24

What are the two types of biological radiation effects

Answer 24

deterministic effect

stochastic effect

Question 25

What is the deterministic effect

Answer 25

§ Tissue reactions
§ Only occur above a certain threshold dose
§ The severity of the effect is related to the dose received
• Unusual to see in radiology although possible in high dose areas such as interventional radiology
• Often the effects will not show immediately but rather several days after the exposure
• Can get skin damage/erythrema

Question 26

What is the stochastic effect

Answer 26

§ Probability of occurrence is related to the dose received. Basis of LNT model
§ No threshold to the effect of severity of the effect is not dependend on dose
○ No dose below which effect will not occur
• Cant predict if they will occur in exposed individual
• Likelihood increases as dose increases
• Can develop years after exposure
• Effect can be divided into somatic or genetic

Question 27

What is the effect of radiation during pregnancy

Answer 27

• Pregnancy does not need to be taken into account for dental radiology
  
  • Fetus must not be radiated inadvertently or beams directed at it
  • In early pregnancy, radiation can damage or kill enough cells for the emrbyo to undergo resorption

Question 28

What are sources of natural background radiation

Answer 28

○ Cosmic rays
○ Radionuclide from diet
Radionuclides in the air

Question 29

What is the effective dose form examinations

Answer 29

• Intra-oral x ray
		○ Negligible risk
	• Lumbar spine x ray
		○ V low risk 
	• Abdominal ct 
		○ Low risk 
	• Cumulative exposures can be bad

Question 30

What legislation makes up radiation protection

Answer 30

• IRMER17 (px)
  
  • IRR18 (staff and public)
  • QA programme for x ray equipment, imaging processing, viewing, image quality

Question 31

What is IRR17

Answer 31

• IRR17
  
  • Controlled areas should extend at least 1.5m from x ray tube and px
  • X ray beam should be directed away from staff

Question 32

What is IRMER 17

Answer 32

• Justification, optimisation (ALARP)
○ Dose optimisation is a legal requirement
○ Make sure dose to px is ALARP
§ Still maintain adequate image quality
§ Circular collimators increase dose by 40% so use rectangular collimator
○ Px dose can be reduced using a variety of methods
§ E speed film or faster
§ Kv range 60-70kv
§ Fsd should be >200mm

Question 33

What are diagnostic reference levels

Answer 33

• Not appropriate to apply this to medical exposures since there is by definition direct benefit to px
  
  • These provide clinical audit tool that can help identify poor ?
  • Legislation requires employers to have established dose levels for typical examinations for standard sized px

Question 34

Why is image quality important

Answer 34

• Keep dose ALARP but enough for image quality as without image quality the exposure is not justified
  
  • CR are prone to damage by teeth marks

Question 35

What is a radiographic risk assessment

Answer 35

• Employer must look at radiation risk assessments
  
  • They should evaluate the risks arising form them
  • Staff scatter exposure is when exposure does not terminate and staff did not follow the procedure of turning off the x ray machine after removing the patient