Pinnacle optimisation
Christian Rønn Hansen
Institute of Medical Physics, School of Physics, University of Sydney, NSW, Australia.
Laboratory of Radiation Physics, Odense University Hospital, Denmark
Agenda
Optimization:
•Pinnacle VMAT optimization
•Iteration effects on cost function
•Objective functions
•Min/Max dose
•Min/Max DVH
•Min/Max EUD
•Optimization efficiency
General TPS issues:
•ISO dose curve evaluation
•Knowledge sharing
•ISO center placement
•Collimation rotation
•Aesthetic dose planning
Optimization
Pitfall of many iterations
0.0010
Pitfall of many iterations
Problems:
Waste of time
Increased complexity for no gain
0.0026
Optimal iteration flow
Cost function
# Iterations
50-100
Dose calculation SVD
Dose changes
25
CC
SVD
20
CC
SVD
15 10
CC
CC CC
SVD SVD SVD
SVD = singular value decomposition
CC = Collapsed Cone Convolution
Objective functions
Objective functions
Min dose = Min DVH (100)
Max dose = Max DVH (0)
Min EUD
a=1
Min EUD
a=-20
Min EUD
a=-40
Min EUD
a=10
Max EUD
a=1
Max EUD
a=20
Max EUD
a=40
Max EUD
a=-20
Max EUD gain at no cost
Medulla
Max EUD gain at no cost
Optimization rings
Max EUD gain at little cost
Oral cavity
Max EUD gain at little cost
Libs
Efficient optimization
Efficient optimization
•Reduce dose grid for optimization
•Turn off DVH’s
•Avoid having the patient open for long periods
•Optimizing over night. Close and delete auto
saved files and reopen in the morning.
•Optimization scripts: Sort objectives
Divide by 10
Interpolate
Will work from 4 degree CP
spacing to 2 degree.
I will not work for 3 degree
CP spacing.
Benefit:
Twice as quick
Downfall:
Need to recalculate dose
No optimisation on new CP
Might forget
Interpolate
Will work from 4 degree CP
spacing to 2 degree.
I will not work for 3 degree
CP spacing.
Benefit:
Twice as quick
Downfall:
Need to recalculate dose
No optimisation on new CP
Might forget
Evaluation issues
PTV50-PTV60
Share knowledge!
Each plan should be discussed with a colleague
Go through:
•Iso centre placement
•Beam setup
•ISO doses
•DVH’s
•Objective functions
•Ask questions:
•Why this?
•Why not this?
•Have you thought about?
•Have you tried?
•Explain your plan:
•I did it because.
•I tried this and this.
•I can’t improve this.
ISO center placement
ISO center placement
Aesthetic dose planning
Aesthetic dose planning
Conclusion
•Pinnacle optimization is not magic. You have all the control you need to steer the
optimization.
•Avoid to many iterations – the plan will not improve just add complexity.
•Used EUD max on OAR or help structures to improve plans without additional cost.
• Spend some time getting familiar with the different input parameters for the
optimization.
• Invest time in setting up the patient, so the optimization is most efficient. More
efficient = better plans, since you can try more ideas.
•Share knowledge with your colleagues – for them and your benefit and in the end
to the benefit of the patient.