Ionising Radiation & Radiation Risk Assessment

Question 1

What can Ionising Radiation be divided into?

Answer 1

1. By-products of radioactive decay- these are alpha particles, beta particles and gamma rays
2. Artificially produced electromagnetic radiation- X-rays

Question 2

What does radiation do when it passes through matter?

Answer 2

It will ionise atoms along it’s path
Each ionisation process will deposit a certain amount of energy locally, approx. 35eV

Question 3

How can radiation cause DNA Damage?

Answer 3

Direct effect
– Radiation interacts with the atoms of a DNA molecule or another important part of the cell
Indirect effect
–Radiation interacts with water in the cell, producing free radicals which can cause damage, free radicals are unstable, highly reactive molecules

Question 4

What DNA damage can usually be repaired?

Answer 4

A single strand break in DNA can usually be repaired

Question 5

How does double stranded DNA damage usually occur?

Answer 5

A result of alpha radiation

Question 6

What tissues are highly radiosensitive?

Answer 6

Bone Marrow
Lymphoid Tissue
Gastrointestinal
Gonads
Embryonic Tissues

Question 7

What tissues are moderately radiosensitive?

Answer 7

Skin
Vascular epithelium
Lung
Lens of the eye

Question 8

What tissues are least radioactive?

Answer 8

CNS
Bone & cartilage
Connective tissue

Question 9

What is the Absorbed Dose?

Answer 9

Measures the energy deposited by radiation and has units of Gray (Gy)

Question 10

What does the Linear No Threshold (LNT) Model estimate?

Answer 10

Estimates the long term biological damage from radiation
It assumes the damage is directly proportional (linear) to radiation dose
It assumes that radiation is always harmful with no safety threshold
–several small exposures would have the effect as one large exposure
–This is known as response linearity

Question 11

What are the 2 types of radiation effects?

Answer 11

Deterministic Effects
–Tissue reactions
–Only occur above a certain (threshold) dose
–The severity of the effect is related to the dose received
Stochastic Effects
–The probability of occurrence is related to the dose received

Question 12

What are the 2 subdivisions of Stochastic Effects?

Answer 12

Somatic- results in disease or disorder
Genetics- abnormalities in descendants

Question 13

What are the effects of radiation during pregnancy?

Answer 13

Could damage or kill enough of the cells for the embryo to undergo resorption
Lethal effects can be induced by doses of 100Gy before or immediately after implantation of the embryo into the uterine wall
During organogenesis (2-8 weeks) when the organs are not fully formed >250Gy can lead to growth retardation
UNLIKELY TO REACH THESE DOSES THROUGH INTRA-ORAL X-RAY

Question 14

How large should the controlled area extend from the X-ray tube and patient?

Answer 14

1.5m

Question 15

What does Justification mean in the Radiation Protection Philosphy?

Answer 15

Practices must have sufficient benefit to individuals or society in order to offset the detriment

Question 16

What does Optimisation mean in the Radiation Protection Philosophy?

Answer 16

Individual doses and the number of people exposed should be kept as low as reasonably practicable (ALARP), taking into account economic and social factors

Question 17

What does ALARP stand for?

Answer 17

As Low As Reasonably Practicable

Question 18

What is the Dose Limitation ?

Answer 18

System of individual dose limits so that the risks to individuals are acceptable

Question 19

What are Diagnostic Reference Levels (DRLs)

Answer 19

Legislation requires Employers to have established dose levels for typical examinations for standard sized patients
They are a comparative standard that is used in optimisation
They are compared to national reference levels

Question 20

How can Patient Doses be reduced?

Answer 20

Use E speed film or faster
Use a kV range of 60kV to 70kV
The focus to skin distance should be >200mm
Use rectangular collimation

Question 21

What are some sources of Natural Background Radiation?
What is the estimated annual background dose?

Answer 21

Air travel, cosmic rays, radionuclides in the air, external gamma radiation
2.2mSv