Answers to revision questions
Chapter 14: Radiation Protection
1. Give two forms of ionising radiation.
Ionising radiation can originate from the x-ray tube or in the form of gamma rays.
2. How will ionising radiation affect cells?
This radiation will damage cells and is not selective of cell type.
3. What will be affected by the genetic effects of radiation?
DNA can be mutated by radiation.
4. What are the three basic principles associated with decreasing radiation exposure?
- No dose limit should be exceeded
- Exposure to personnel should be kept to a minimum
- Unnecessary procedures should not be performed
5. Which guidelines should be followed?
Ionising Radiation Regulations 1999.
6. What is the RPA?
Radiation protection advisor.
Someone outside the practice with specialised radiation experience.
7. Give three points that the local rules should include.
- No animal is manually restrained
- No unnecessary personnel stay in the room during exposure
- Suitable protection is used
- Predetermined guidelines for pregnant members of staff
- Minimum age of 16 for trainee staff
- Areas within the practice are classified
- Guidelines for the implementation of warning signs during exposure.
8. Who devises the systems of work?
The system of work is devised by the radiation protection supervisor with the support of the radiation protection advisor.
9. What type of walls should a controlled area have?
The controlled area should have walls that do not allow penetration of the x-ray beam. It should be 2 bricks thick or coated in special barium plaster.
10. Where is the supervised area?
A supervised area surrounds the controlled area. This is any area that exceeds 1/10 of the recommended dose limit and therefore control of personnel entering this area needs to be monitored.
11. What is the minimum age of a classified worker?
Anyone working in an x-ray room should be at least 16years old.
12. How does a film badge record the dose received?
A small film is placed in a plastic container. A number of different ports have varying thicknesses and types of metal. When the film is developed the degree of blackening on the film and the regions that are blackened will determine the dose received. The films are sent away for analysis and can only be used once making them expensive.
13. How does a TLD work?
It contains crystals of lithium fluoride, which has a similar density to soft tissues. After the dosimeter has been worn and possibly irradiated, it is heated and the amount of light emitted is compared to a standard, known radiation dose. The dose received can then be calculated. This type of monitor can be re-used.
14. List three QA tests or procedures that can be carried out easily by a practice.
The accuracy of the light-beam diaphragm can be checked within the practice very easily and can rectify disputes over collimation practice. The primary beam is collimated to a square about 5cm smaller than the cassette. Paper clips are unwound and placed on the corners of the visible collimation. Using a low exposure, the film is exposed. This is then processed. On viewing the edge of the collimation should be at the same place as the paper clips. Any variation will demonstrate the inaccuracy of the collimators.
The rollers and tanks of the processor should be thoroughly washed with fresh running water. The temperature of the wash water and the developer should be checked, as these will influence the activity of the processing chemistry and the quality of the resultant image.
Replenishment should be ongoing, as tired chemistry will reduce the effectiveness of the developing and fixing agents.
Sensitometry and densitometry should be carried out to ensure the maintenance of constant processing conditions.