Ionising Radiation & Radiation Risk Assessment Flashcards
What can Ionising Radiation be divided into?
- By-products of radioactive decay- these are alpha particles, beta particles and gamma rays
- Artificially produced electromagnetic radiation- X-rays
What does radiation do when it passes through matter?
It will ionise atoms along it’s path
Each ionisation process will deposit a certain amount of energy locally, approx. 35eV
How can radiation cause DNA Damage?
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
What DNA damage can usually be repaired?
A single strand break in DNA can usually be repaired
How does double stranded DNA damage usually occur?
A result of alpha radiation
What tissues are highly radiosensitive?
Bone Marrow
Lymphoid Tissue
Gastrointestinal
Gonads
Embryonic Tissues
What tissues are moderately radiosensitive?
Skin
Vascular epithelium
Lung
Lens of the eye
What tissues are least radioactive?
CNS
Bone & cartilage
Connective tissue
What is the Absorbed Dose?
Measures the energy deposited by radiation and has units of Gray (Gy)
What does the Linear No Threshold (LNT) Model estimate?
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
What are the 2 types of radiation effects?
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
What are the 2 subdivisions of Stochastic Effects?
Somatic- results in disease or disorder
Genetics- abnormalities in descendants
What are the effects of radiation during pregnancy?
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
How large should the controlled area extend from the X-ray tube and patient?
1.5m
What does Justification mean in the Radiation Protection Philosphy?
Practices must have sufficient benefit to individuals or society in order to offset the detriment
What does Optimisation mean in the Radiation Protection Philosophy?
Individual doses and the number of people exposed should be kept as low as reasonably practicable (ALARP), taking into account economic and social factors
What does ALARP stand for?
As Low As Reasonably Practicable
What is the Dose Limitation ?
System of individual dose limits so that the risks to individuals are acceptable
What are Diagnostic Reference Levels (DRLs)
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
How can Patient Doses be reduced?
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
What are some sources of Natural Background Radiation?
What is the estimated annual background dose?
Air travel, cosmic rays, radionuclides in the air, external gamma radiation
2.2mSv
