What’s next in IMRT? - Optimizing the Optimization - T. Bortfeld 1, C. Thieke 1,2, K.-H. Küfer 3,...
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Transcript of What’s next in IMRT? - Optimizing the Optimization - T. Bortfeld 1, C. Thieke 1,2, K.-H. Küfer 3,...
What’s next in IMRT?What’s next in IMRT?- Optimizing the Optimization - - Optimizing the Optimization -
TT.. Bortfeld Bortfeld11, C. Thieke, C. Thieke1,21,2, K.-H. Küfer, K.-H. Küfer33, H. Trinkaus, H. Trinkaus33
11Department of Radiation Oncology, Department of Radiation Oncology, Massachusetts General Hospital, Boston, USAMassachusetts General Hospital, Boston, USA
22Department of Medical Physics, Department of Medical Physics, Deutsches Krebsforschungszentrum, Heidelberg, Germany,Deutsches Krebsforschungszentrum, Heidelberg, Germany,
33Fraunhofer Institut für Techno- und Wirtschaftsmathematik, Fraunhofer Institut für Techno- und Wirtschaftsmathematik, Kaiserslautern, GermanyKaiserslautern, Germany
Current technical/physical developments in IMRTCurrent technical/physical developments in IMRT
• Make IMRT more efficientMake IMRT more efficient– Streamlined, integrated solutionsStreamlined, integrated solutions– Minimize MLC segmentsMinimize MLC segments– Optimized inverse planningOptimized inverse planning
• Make IMRT more accurateMake IMRT more accurate– Better dose calculation (superposition, MC)Better dose calculation (superposition, MC)– Image guidanceImage guidance– Online verification with portal imagingOnline verification with portal imaging– Gating/Tracking to reduce breathing artifactsGating/Tracking to reduce breathing artifacts– Proton and heavy ion IMRTProton and heavy ion IMRT
Current technical/physical developments in IMRTCurrent technical/physical developments in IMRT
• Make IMRT more efficientMake IMRT more efficient– Streamlined, integrated solutionsStreamlined, integrated solutions– Minimize MLC segmentsMinimize MLC segments– Optimized inverse planningOptimized inverse planning
• Make IMRT more accurateMake IMRT more accurate– Better dose calculation (superposition, MC)Better dose calculation (superposition, MC)– Image guidanceImage guidance– Online verification with portal imagingOnline verification with portal imaging– Gating/Tracking to reduce breathing artifactsGating/Tracking to reduce breathing artifacts– Proton and heavy ion IMRTProton and heavy ion IMRT
Change “penalties” or “weight factors”Change “penalties” or “weight factors”
Weight factor approachWeight factor approach
OptimizeOptimize
FF is a single number! is a single number!
Risk2Risk2Risk1Risk1TargetTarget FwFwFwF
Difficulty 1Difficulty 1
• By how much do you change the weight By how much do you change the weight factors, factors, w w ??– Trial and errorTrial and error
Example: Head&NeckExample: Head&Neck
Brainstem
Spinal Cord
Parotis
0 25 50 75 1000
20
40
60
80
100 Plan 1
Target
Spinal Cord
Vo
lum
e (
%)
Dose (Gy)
Plan 2
w=10000
w=1
Difficulty 2Difficulty 2
• ““Sensitivity” of the solution?Sensitivity” of the solution?
Difficulty 3Difficulty 3
Constraint optimization:Constraint optimization:
Solutions may not be “efficient”!Solutions may not be “efficient”!
Example: Head&NeckExample: Head&Neck
Brainstem
Spinal Cord
Parotis
0 25 50 75 1000
20
40
60
80
100 Plan 1 Plan 2
Target
Brainstem
Spinal Cord
Vo
lum
e (
%)
Dose (Gy)
Optimization of the Optimization: SolutionsOptimization of the Optimization: Solutions
1.1. Use Equivalent Uniform Dose (EUD) to Use Equivalent Uniform Dose (EUD) to characterize the dose in every relevant characterize the dose in every relevant structurestructure
2.2. Find efficient (“Pareto optimal”) solutionsFind efficient (“Pareto optimal”) solutions
3.3. Calculate database with representative Calculate database with representative solutions, use interpolationsolutions, use interpolation
Solutions, part 1Solutions, part 1
• Use Equivalent Uniform Dose (EUD)Use Equivalent Uniform Dose (EUD)– A. Niemierko “A generalized concept of A. Niemierko “A generalized concept of
equivalent uniform dose (EUD)” equivalent uniform dose (EUD)” Med. Phys. 26:1100, 1999Med. Phys. 26:1100, 1999
EUD = uniform dose to the organ that leads EUD = uniform dose to the organ that leads to the same effectto the same effect
EUD exampleEUD example
0
25
50
75
100
0 20 40 60
Vo
lum
e [%
]
Dose [Gy]80 100
Question: What is the homogeneous dose that would give the same effect?
Lung:EUD = 25 Gy
Spinal Cord:EUD = 52 Gy
Power-Law (p-Norm) ModelPower-Law (p-Norm) Model
p
i
pii Dv
/1
EUD
“p-norm”
Mohan et al., Med. Phys. 19(4), 933-944, 1992Kwa et al., Radiother. Oncol. 48(1), 61-69, 1998Niemierko, Med. Phys. 26(6), 1100, 1999
Examples:
:
:1
p
p
maxEUD
EUD
D
D
Solutions, part 2Solutions, part 2
• Find efficient (Pareto optimal) solutionsFind efficient (Pareto optimal) solutions
0 25 50 75 1000
20
40
60
80
100
TargetEUD = 70 Gy
Brainstem
Spinal CordEUD = 34 Gy
Vo
lum
e (
%)
Dose (Gy)
EUD=25 Gy
Efficient (Pareto optimal) Plan
EUD=10 Gy
Solutions, part 3Solutions, part 3
• Fill database with solutions for different Fill database with solutions for different combinations of EUD valuescombinations of EUD values(over night)(over night)
SummarySummary
• New concept in IMRT optimizationNew concept in IMRT optimization
• Multi-criteria EUD optimizationMulti-criteria EUD optimization
• Find better solution fasterFind better solution faster
Power-Law (p-Norm) ModelPower-Law (p-Norm) Model
nvv
)1(TD)(TD
Power-law relationship for tolerance dose (TD):
0 25 50 75 1000
20
40
60
80
100 Plan 1
Target
Spinal Cord
Vo
lum
e (
%)
Dose (Gy)
Plan 2EUD=50.2 Gy
EUD=72.4(a=-8)
EUD=4.0(a=-8)
EUD=18.7 Gy