Quality Control Procedures

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Quality control procedures are the procedures needs done at a time to improve and maintain the quality of the treatment. Quality control procedures are almost similar for telecobalt and linear accelerators (external beam radiotherapy).  

The quality control procedures for External Beam Radiotherapy:

 Mechanical Checks:

1. Check of optical SSD indicators

2. Collimator, gantry and treatment table rotation scales

3. Treatment table movement scales

4. Treatment table top deflection under load

5. Light and radiation field coincidence

6. Mechanical isocentre check

7. Rotation axis of the collimator

8. Treatment table rotation

9. Rotation axis of the gantry

10.Radiation isocentre check

11.‘Star film’

12.Alignment of opposing fields

13.Laser alignment

14.Field size indicators


Radiation Checks X-rays:


1. Beam output: definitive calibration, routine beam output check, constancy check

2. Output constancy with gantry angle

3. Output constancy with dose rate

4. Linearity of the dosimetry system

5. Dose monitor leakage

6. Output factors

7. Tray transmission factors

8. Wedge factors (mechanical wedges)

9. Wedge factor constancy with gantry angle

10. Beam energy

11. Dose profiles at reference gantry position

12. Dose profile constancy with gantry angle

13. Gantry rotation speed / MU delivered per unit angle  interval

14. Radiation leakage

15. Radiation survey


Checks relating to the mechanical integrity and safety of the machine:

1. Room entrance interlock
2. Manual door opening
3. Audio video monitor
4. Beam on indicators
5. Emergency off switches
6. Touch guards
7. Brakes
8. Dead-mans switches
9. Accessory (tray and wedge) interlocks
10. Trays, wedges, blocks and electron applicators
11. Backup Dose Monitor Interlock
12. Timer function
13. Patient retrieval in case of power failure


Multileaf collimator (MLC)

1. Shape of MLC fields
2. Alignment of leaf positions
3. Alignment of opposing leaves
4. Interlocks
5. Leakage between leaves

Dynamic wedges

1. Dynamic wedge factors
2. Interrupted dynamic wedge exposures
3. Dynamic wedge profiles
4. Dynamic wedge factor variation with gantry angle

The details of aims, procedures and practicing parts are given in the reference 1 mentioned below.

Questions:

1. Choose the correct mechanical check procedure?

a) Radiation output verification

b) SSD verification

c) light and radiation field verification

d) all of these

1.a and b only

2. b and c only

3. d

4. A, b, and c


Answer:

b and c only


References:

1. Quality control for medical electron accelerators, recommendation 11

2.The physics of radiation therapy

Home > Radiation Protection and Quality Assurance > Equipment Use & Quality Assurance > Quality Control Procedures

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