1. Optimization of Gamma Knife Radiosurgery
Michael Ferris
University of Wisconsin, Computer Sciences
David Shepard
University of Maryland School of Medicine

2. Overview Details of machine and problem Formulation Results
modeling dose
shot / target optimization
Results
Two-dimensional data
Real patient (three-dimensional) data

6. The Leksell Gamma Knife

8. Problem characteristics
Machine has 201 radiation sources focussed on one location
Very accurate dose delivery
Benefits of computer solution
uniformity of treatment plan
better treatment plan
faster determination of plan

9. Problem outline Target volume (from MRI or CT)
Maximum number of shots to use
Which size shots to use
Where to place shots
How long to deliver shot for
Conform to Target (50% isodose curve)
Real-time optimization

10. Two-dimensional example

11. Ideal Optimization

13. Dose calculation Measure dose at distance from shot center
Fit a nonlinear curve to these measurements
Functional form from literature, 6 parameters to fit via least-squares

14. 8mm shot

15. Nonlinear Approach

16. Two-stage approach Approximate via “arctan”
First, solve with approximation, then fix shot widths and reoptimize

17. 3D slice image

18. Slice + 3

19. Axial slice
Manual Computer Optimized

20. Axial slice
Manual Computer Optimized

21. Coronal slice
Manual Computer Optimized

22. Sagittal slice
Manual Computer Optimized

23. Challenges Integration into real system Reduction of optimization time
What if scenarios?
Improve the objective function
Change number of shots
Global versus local solutions