37. CT: DOSE REDUCTION

Question 1

1. Can clinically adequate images be obtained with lower exposure levels?

Answer 1

• yes they can
• this is what drives the development of improved
  technologies
• it is what drives the re-examination of long-accepted
  protocols
• it is even helping to modify physician and technologist
  behaviour

Question 2

2. What can be said about the cost of all these developments?

Answer 2

• it is happening with very little increase in cost
• or time

Question 3

3. Why is so much improvement happening?

Answer 3

• there is a growing awareness of the need for
  improvements in dose reduction

Question 4

4. Name 3 programs that are helping with the improvements in Dose Reduction.

Answer 4

1. Image Gently
2. ESR EuorSafe Imaging
3. International Recommendations

Question 5

5. What percentage of CT exams on children are medically not necessary?

Answer 5

• 30%
• these tests could rather be carried our with safer
  techniques
• such as US’s or MRIs

Question 6

6. What can be said about the specificity of CT protocols for specific types of studies?

Answer 6

• they are site specific
• they are physician specific

Question 7

7. What is an effective way of reducing the dose?

Answer 7

• the facility must undertake a comprehensive
  comparison of its own protocols
• it must also consider the protocols of other facilities
  that use the same type of machine

Question 8

8. How much can doses be reduced by while still providing adequate image quality?

Answer 8

• they can reduce by 50%
• this can be achieved by a single change of kVp

Question 9

9. What effect does reducing the current per rotation
   (mA-s) have on the Dose?

Answer 9

• it reduces it by 10%

Question 10

10. What two steps needed to create a Dose Reduction Program?

Answer 10

1. Selecting a different diagnostic modality
2. Considering the overall Clinical impact of a study
3. If you do choose to image with CT:
   
   • fit the scanning parameters to the patient’s
   • body shape
   • size
   • age
4. Encourage your organisation to re-appraise the
   benefit-dose tradeoff of the current scanning
   protocols

Question 11

11. What do we take into consideration when we: “Select a different diagnostic modality”?

Answer 11

• if it is possible to obtain the needed information
  without any ionising radiation
• consider the cost
• consider all the possible examination delays

Question 12

12. What do we take into consideration when we:
    “Consider the overall clinical impact of a study”?

Answer 12

WE DO NOT PERFORM THE CT PROCEDURE:
- if it is not likely to change the patient treatment
- if it is not likely to follow-up significantly

Question 13

13. What do we take into consideration when we:
    “Fit the scanning parameters to the patient’s body shape, size and age”?

Answer 13

• we will tolerate images that have some degree of noise
• as long as the study is still deliverable

Question 14

14. What have organisations around the world started doing?

Answer 14

• they have begun actively collaborating
• they are re-examining the scanning parameters

Question 15

15. What do Technique charts list?

Answer 15

• they list ways to modify current adult’s protocols
• this makes them more suitable for children

Question 16

16. What do CT vendors incorporate?

Answer 16

• they incorporate various forms of Automatic Exposure
  Control Circuits
• this is known as mA modulation

Question 17

17. List 2 other methods of helping to reduce the Dose?

Answer 17

1. Involving control of the kVp
2. Reducing exposure of the female breast
3. Sculpting the edge of the beam
   - this is done at the end of the region of clinical interest
   - this will cut down the irradiation of tissues that are
   outside the region of interest