Introduction to Sports Injuries by- Dr. Anjali Rai
Inverse Planning
1. Intensity-Modulated Radiotherapy and Inverse Planning C-M Charlie Ma, Ph.D. Department of Radiation Oncology Fox Chase Cancer Center Philadelphia, PA 19111, USA
7. IMRT - A Complex Process Planning Position Verification target localization Delivery Plan Verification Treatment Delivery and Verification Structure Segmentation Treatment Optimization Patient Immobilization
8. Bite-block Head Holder Immobilization Aquaplast Breath Control Spirometer Vacuum frame
20. Conventional treatment planning starts with a set of beam weights and obtains a plan by a trial-and-error process. This procedure won’t work for IMRT since there are too many unknowns (>2000 beamlet weights). How can we determine the individual beamlet weights for IMRT ?
23. What is in an Inverse Planning System? Dose calculation Interface with R&V Optimization Patient data Leaf sequencing
24. D i = C ij W j -- Weight for beamlet j w j C ij -- dose contribution in voxel i from beamlet j in an open beam i j
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27. However, Unfortunately this inverse process does not work in most, if not all, realistic treatment cases. Practically, what we want is a set of beamlet weights that will give us the best available dose distribution ! is an exact mathematical expression of inversely derived beamlet weights for a desired dose distribution D 0
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31. There are many ways to optimize a treatment plan for a given objective function (forward, backward, hybrid, etc)! An inverse planning system may use any optimization algorithms (more likely it is a forward planning, or a hybrid, process). There are many ways to build an objective function (everybody wants his/her own)!
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33. Major differences between optimization systems are the construction of the objective function and the methods for search directions and step-length Most optimization methods use an iterative approach, one way or another
37. Parallel Vector Method Global minimum Independence and local minimum avoidance 100 50 25 75
38. How Inverse Planning Is Done? Inside a computer W is generally not optimal Optimal Input W Output D 0 Compute C Change W b Compute D b =CW b Evaluate O=f(D b -D 0 )