Commissioning Flashcards
Life cycle of linac (8)
Bunker build and preparation
Installation
Environmental radiation survey
Critical evaluation
Customer acceptance
Commissioning
Clinical Use
De-commissioning
Why do commissioning (3)?
Need to characterise MV radiation performance of linac
Need to ensure everything works as expected
Acquire baseline performance metrics for commissioning period and clinical life
Why do we have to do commissioning legally?
IRR
Medical and dental guidance notes
What are we commissioning?
TPS
Secondary check systems
Manual calculation systems
kV and MV imaging systems
Other systems such as 6dof couch
Don’t use anything clinically unless physics have commissioned it
What do we do for TPS/secondary check software typically?
Required data and measurement conditions are generally well defined in beam modelling guide, range of fields, SSDs, resolution, output factors, PDDs and profiles, Sc and Sp, for every photon energy
Manual software requires own definitions of required measurements
What equipment might be used?
Water tank
Detectors
Electrometers
1D/2D arrays
Mini phantoms and build up caps
What is effective point of measurement?
Location of point in medium that the detector signal would come from in the absence of a detector.
Typically displaced toward the source of radiation for cylindrical ion chamber
Why is TPS commissioning important?
Some accidental exposures were associated with lack of understanding of TPS, lack of appropriate commissioning, lack of independent calc. checks
What are some TPS things we need to check?
Dosimetric/geometric treatment machine model
Data transfer integrity
Conversion of CT no. to ED
Image handling - DRR, 3D reconstruction, image registration, contouring tools etc
Dose display, DVH calculations
Inverse planning optimisation tools
Planning documentation
Clinical workflows, end to end testing
Other - anonymisation, user rights, cyber-security
Considerations for beam model
High quality beam data (PDD, profiles, OF)
Matched machines
Manufacturers instructions
How do we test the beam model?
Use independent data
Cover range of clinical uses, including different field sizes, SSDs, treatment techniques
Test extreme cases
Why do we need to characterise MV performance under different conditions?
So correct data is fed into TPS and check software
What can go wrong with a water tank?
Evaporation
Lift mechanism sag
Crashing of drive mechanisms
Trapping of cables
Changing detectors
People tampering
What needs to be considered when setting a tank up?
Beam and tank co-ordinate system need to be parallel
Tank must be flat
Confirm set up by scanning at cross plane and in plane at two different depths
