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Direct Consideration of EUD Constraints in IMRT Optimization

Direct Consideration of EUD Constraints in IMRT Optimization. Ch. Thieke 1,2 , Th. Bortfeld 1 , A. Niemierko 1 , S. Nill 2. 1. Dept. of Radiation Oncology Massachusetts General Hospital Boston, MA. 2. Dept. of Medical Physics Deutsches Krebsforschungszentrum Heidelberg Germany. Contents.

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Direct Consideration of EUD Constraints in IMRT Optimization

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  1. Direct Consideration of EUD Constraints in IMRT Optimization Ch. Thieke1,2, Th. Bortfeld1, A. Niemierko1, S. Nill2 1 Dept. of Radiation Oncology Massachusetts General Hospital Boston, MA 2 Dept. of Medical Physics Deutsches Krebsforschungszentrum Heidelberg Germany

  2. Contents • Constraints in IMRT optimization • Projection onto convex sets • Clinical case • Conclusions

  3. max D Maximum dose constraint Volume Dose

  4. max V max D DVH constraint Volume Dose

  5. EUD constraint I Equivalent uniform dose, EUD: Niemierko, MedPhys 1999 Tumor: a negative Normal tissue: a positive

  6. EUD constraint II Volume Dose

  7. POCS – Projection onto convex set D2 D x D‘ x Convex set D1

  8. POCS – Math I Extrema on a bounded surface • Use Lagrange Multipliers

  9. POCS – Math II Implicit definition of new dose constraint D‘j in voxel j: • Single EUD constraint  individual physical constraints for every organ voxel • Easy to implement into existing IMRT planning tools (keep objective function, gradients, optimization alg.)

  10. POCS – Example Serial Organ

  11. POCS – Example Serial/Parallel Organ

  12. POCS – Example Target

  13. Clinical case: head and neck tumor Brainstem Parotid Target Spinal cord

  14. Results

  15. Conclusions • EUD constraints can be used for easy to handle, yet clinical meaningful IMRT optimization • Projection onto convex set (POCS) converges fast and stable • Mixing of physical constraints and EUD contraints is possible • Presented method is easy to integrate into existing IMRT planning tools based on physical dose constraints

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