Acceptance, comissioning and QA of Cobalt and LINAC

1. Acceptance , Commissioning and
Quality Assurance of Cobalt and
Linear Accelerator
Dr Chandana Sanjee
DNB Resident

2. Contents
• Introduction
• Acceptance definition
• Commissioning definition
• Equipment's used for Acceptance, Commissioning
and QA
• Acceptance tests
• Commissioning tests
• QA for Cobalt according to AAPM TG 40
• QA for LINAC according to AAPM TG 40
•

3. Introduction
ICRU recommends 5% accuracy in tumor dose
delivery. The links constituting this chain are
1. Calibration of external beam radiotherapy
2. Equipment commissioning and QA
3. Treatment planning
4. Patient set up on the treatment machine

4. Acceptance tests
• These tests assure that the specifications contained
in the purchase order are fulfilled and that the
environment is free of radiation and electrical
hazards to staff and patients
• These are performed in presence of manufacturer’s
representative
• After completion final payment is made and
ownership of unit is transferred

5. Commissioning
• Commissioning means making the machine ready for
patient use . This required physics data generation needed
by the TPS
• Commissioning of an EBRT device includes a series of
tasks that include
1. Acquiring all radiation beam data
2. Organizing these data into a dosimetry data book
3. Entering these data into TPS
4. Developing all dosimetry, treatment planning and
treatment procedures
5. Verifying the accuracy of these procedures
6. Establishing QC tests and procedures
7. Training all personnel

6. Equipment required for Acceptance and
Commissioning and QA
1.Geiger counter-
Geiger counters are used to
detect radioactive emissions,
most commonly beta particles
and gamma rays.
The counter consists of a tube
filled with an inert gas that
becomes conductive of
electricity when it is impacted
by a high-energy particle

7. 3.Thimble chamber/Farmer chamber
-Wall made of graphite
-Electrode of Al
-Insulator consists of
polytrichlorofluroethylene
-Volume ranges from 0.1-0.6cm3
-Thimble is at ground potential
- Most often collecter is operated at
positive volatge to collect negative
charges

8. 5.Radiographic film – Used in X-rays
Not tissue equivalent
6.Radiochromic film-
Tissue equivalent
Insensitive to light
No need for chemical processing
Consists of radio-sensitive dye
sandwiched between 2 pieces of
polyester base

9. 7.Phantoms(water ) / RFA

10. 8. Front pointer- Used for
Optical Density Indicator (
SSD) Quality assessment

11. Acceptance tests
• Safety checks
1. Interlocks, warning lights and Patient monitoring
equipment
2. Radiation survey
3. Collimator and Head leakage

12. • Door interlocks- Prevents irradiation when treatment
door is open.
• Emergency off interlocks-Disable power to motors
and RT machine

13. • Photon measurements radiation survey- Geiger
counter, ionisation chamber survey meter
• Neutron measurement – Bonner sphere, long
counter, BF3 counters
• All primary barriers should be surveyed with largest
field size with collimator rotated to 45degrees and
no phantom in beam. Secondary barriers without
phantom
• First area to be surveyed will be control console
•

14. • Safety – Workflow
-While the machine is on, open the vault door to ensure the
beam turns off (door interlock)
-Verify that the machine cannot beam back on until the door is
shut (door closing safety)
-Once the machine is on, verify that the radiation monitor
(radiation area monitor) and beam-on indicator lights are
working (beam-on indicator).
-Verify that you can see the treatment table on the closed
circuit monitors and that you can hear sound from inside the
vault using the A/V system (audiovisual monitor)

15. • Collimator and head leakage
• Shield surrounds the target of LINAC or source on a
Cobalt 60
• Accepted is 0.1% of the useful beam at 1m from
source.
• Adequacy of shielding must be verified.

16. • Mechanical checks
1. Collimator axis rotation
2. Photon collimator jaw motion
3. Congruence of light and radiation field
4. Gantry axis rotation
5. Patient treatment table axis of rotation
6. Radiation IC
7. Optical distance indicator
8. Gantry angle indicator
9. Collimator field size indicators
10.Patient treatment table motions

17. • Dosimetry measurements
1. Photon energy
2. Photon beam uniformity
3. Photon penumbra
4. Electron energy
5. Electron beam bremsstrahlung contamination
6. Electron beam uniformity
7. Electron penumbra
8. Monitor characteristics
9. Arc therapy

18. • Commissioning
• Photon beam measurements
• -CA PDD
• -Output factors
• -Block tray factors
• -MLC
• -Central axis wedge transmission factors
• -Dynamic wedge
• -Transverse beam profile / Off axis energy changes
• -Entrance dose and interface dosimetry
• -Virtual source position

19. • Commissioning
• Electron beam measurements
• CA PDD
• Output factors
• Transverse beam profiles
• Virtual source position
•
•

20. • Commissioning
• Time taken for commissioning is about 1.5-3 weeks
per energy following completion of acceptance. It
depends on
• Machine reliability
• Amount of data
• Sophistication of treatments planned
• Experience of physicist

21. QA of Cobalt 60 -Daily
• Safety
1. Door interlock Functional
2. Radiation room monitor Functional
3. AV monitor Functional
• Mechanical
1. Laser 2mm
2. Distance indicator 2mm

22. Weekly
Safety and Mechanical
1. Check for source positioning 3mm

23. Monthly
• Dosimetry
1. Output constancy 2%
• Mechanical checks
1. Light / radiation field co-incidence 3mm
2. Field size indicator 2mm
3. Gantry and collimator angle indicator 1degree
4. Cross hair centering 1mm
5. Latching of wedges and trays Functional
• Safety checks
1. Emergency off Functional
2. Wedge interlocks Functional

24. Annual
• Dosimetry
1. Output constancy 2%
2. Field size dependence of output constancy 2%
3. Electron central axis dosimetry parameter constancy
(PDD,TAR,TPR) 2%
4. Transmission factor constancy for all standard accessories 2%
5. Wedge transmission factor constancy 2%
6. Time linearity and error 1%
7. Output constancy vs gantry angle 2%
8. Beam uniformity vs gantry angle 3%

25. • Safety Interlocks
• Mechanical checks
1. Collimator rotation IC 2mm diameter
2. Gantry rotation IC 2mm diameter
3. Couch rotation IC 2mm diameter
4. Coincidence of gantry,
collimator, couch axis with IC 2mm diameter
5.Coincidence of radiation and mechanical IC 2mm diameter
6. Table top sag 2mm diameter
7. Vertical travel of table 2mm diameter
Field light intensity Functional

26. Quality assessment for LINAC
• The data fed into the TPS at the time of
commissioning must be tested at regular intervals to
check their validity.
• The aim of RT is that “Prescription must be
delivered”
• It is not possible to examine all data everyday.
• A time bound program is fixed for quality checks
namely daily tests , monthly tests and annual tests

27.  X-Ray and Electron Output, Backup Monitor Chamber, Typical Dose-Rate
Output and Electron Beam Energy Constancy Tests
Recommended Items
-Ion chamber
-Electrometer
-Solid water or water tank
Workflow
Measure X-ray and electron output under reference conditions established at the
time of commissioning for all energies, and verify that the backup monitor
chamber is within tolerance of the primary monitor chamber.
Repeat the X-ray and electron output measurements at different dose rates to
verify dose-rate output constancy. (This is necessary because the RF driver and
gun current are tuned independently for each energy.)
Measure electron beam energy constancy by comparing full profiles (water tank)
or output ratios at different depths (solid water). Verify that the acquired values
are within a one percent tolerance from baseline values.

28. Daily tests
1. X-ray output constancy 3%
2. Electron output constancy 3%
3. Lasers 2mm
4. Distance indicator 2mm
5. Door interlock Functional
6. Audiovisual monitor Functional

29. Monthly
1. X-ray and electron output constancy 2%
2. Backup monitor constancy 2%
3. X-ray CAD parameter constancy
(PDD,TAR,TPR) 2%
4. Electron CAD parameter constancy 3%
5. X ray beam flatness constancy 2%
6. Electron beam flatness constancy 3%
7. X ray and Electron symmetry 3%

30. Monthly tests
8. Emergency off switches
Functional
9. Wedge and electron cone interlocks
Functional
10. Light/ Radiation field co-incidence
2mm
11. Gantry/ collimator angle indicators
1degree
12. Wedge position 2mm(or 2% change in
transmission factors
13. Tray position and Applicator position

31. Monthly
14.Treatment table position indicators 2mm
15.Latching of wedges and blocking tray
Functional
16.Jaw symmetry 2mm
17.Field light intensity Functional

32. Annual
1. X-ray/Electron output calibration constancy
2%
2. Field size dependence of X ray output
constancy2%
3. Output factor constancy for electron applicators2%
4. Central axis parameter constancy(PDD,TAR,TPR)
2%
5. Off axis treatment constancy
2%
6. Wedge transmission factor constancy
2%

33. Patient specific QA in IMRT
• A phantom plan is generated in 0 degree gantry
position.
• The plan is to measure dose at isocenter located at
5/10cm depth in the phantom
• All IMRT fields deliver a dose of 200cGy at IC.
• An ion chamber is fixed at IC for dose measurement

34. Thank You