59. RADIOTHERAPY: PARTICLE ACCELERATORS

Question 1

1. What is the function of Accelerators?

Answer 1

• they have been built for basic research in nuclear and
  high energy physics

MOST OF THESE ACCELERATORS:
- have been modified for the use in Radiotherapy

Question 2

2. What are the 2 basic conditions that must be met for Particle Acceleration?

Answer 2

1. The particle must be charged
2. The electric field must be provided in the direction of
   particle association

Question 3

3. What is the purpose of the Electric Field?

Answer 3

• to propagate the electrons

Question 4

4. What distinguishes between the various types of accelerators?

Answer 4

1. The way in which they produce the accelerating
   electric fields
2. How the field acts on the particles to accelerate them

Question 5

5. What are the two main classes of Accelerators when it comes to the accelerating electric field?

Answer 5

1. Electrostatic
2. Cyclic

Question 6

6. List the examples of Electrostatic accelerators used in Medicine.

Answer 6

1. Superficial X-Ray tubes
2. Orthovoltage X-Ray tubes
3. Neutron Generators

Question 7

7. What is the best known example of a Cyclic Accelerator?

Answer 7

• the Linear Accelerator (LINAC)

OTHER EXAMPLES ARE:
- Microtrons
- Betatrons
- Cyclotrons

Question 8

8. What do Medical LINACs do with electrons?

Answer 8

• they accelerate electrons to kinetic energies
• these range from 4 to 25 MeV
  (Mega Electron Volts)
• they are accelerated following Straight Trajectories
• this is why they are called Linear Projections

Question 9

9. In which contraption do LINACs accelerate electrons?

Answer 9

• LINACs act in Special Evacuated structures
• these are called Accelerating Waveguides

Question 10

10. What path do electrons follow?

Answer 10

• they follow a linear path
• they travel through the same potential difference
• this potential difference is relatively low
• they do this several times

Question 11

11. What kind of Radio Fields are used for electron acceleration?

Answer 11

• high power Radio Fields

Question 12

12. What kind of X-Rays doe LINACs provide in the Clinical Setting?

Answer 12

1. SOME PROVIDE X-RAYS
   - that are only in the low Mega Voltage Range
   - this is about 4 or 6 MV
2. OTHER PROVIDE BOTH X-RAYS AND ELECTRONS
   - at various Mega Voltage Energies

Question 13

13. What is the product of a typical, modern, high-energy LINAC?

Answer 13

1. 2 PHOTON ENERGIES
   - one that is 6 MV
   - the other is 18 MV
2. SEVERAL ELECTRON ENERGIES
   - 6 MeV
   - 9 MeV
   - 12 MeV
   - 16 MeV
   - 22 MeV

Question 14

14. What is the issue with the complexity of modern LINACS?

Answer 14

• it raises concerns regarding the Operational safety

Question 15

15. Which organisation publishes the International standards of safety when dealing with LINACs?

Answer 15

• the International Electrotechnical Commission
• the IEC

Question 16

16. What does the IEC statement of safety of LINACs state?

Answer 16

THE PATIENT MAY BE EXPOSED TO DANGERS:
- if the equipment fails to deliver the required dose
- if the equipment dose does not satisfy mechanical and
electrical safety
- if the equipment fails to contain the radiation
adequately
- inadequacies in the treatment room

Question 17

17. What happens if the equipment fails to contain the radiation adequately?

Answer 17

• people outside of the treatment room can be harmed

Question 18

18. Which three categories of safety issues does the IEC document address?

Answer 18

1. Electrical
2. Mechanical
3. Radiation

Question 19

19. What kind of requirements does the IEC have with regards to LINACs?

Answer 19

IT HAS SPECIFIC REQUIREMENTS:
- in the design
- in the construction
- of LINACs