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February
2, 2001 Abstract |
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Radiation treatment planning requires the calculation of a set of parameters for the delivery of a certain radiation dose to the patient. Ideally, radiation dose distribution should be designed to conform perfectly to the entire tumor volume while completely avoiding surrounding normal tissues. Although achievement of this goal is practically impossible, a computer optimization can potentially simplify the tedious planning procedure and yield the best possible plans. Computer optimization becomes necessary for intensity modulated radiation therapy (IMRT) treatment planning because of the vast number of beamlet weights involved in the problem. In general, the computer optimization is realized by using so called inverse treatment planning technique which derives a set of optimized beam parameters by starting from a prescribed dose distribution. In this talk, I will present an overview of various inverse planning approaches. In general, the work in inverse treatment planning can be classified into the two categories: (1) modeling to improve our understanding of the biological effects of radiation by incorporating various physical, biological, and other effects into an objective function; and (2) methods to search for the minimum (or maximum) of the objective functions. An inverse planning requires to construct an objective function to establish a link between the output dose distribution and the input beam parameters. The objective function measures the goodness of a selected plan and its choice is crucial for therapeutic plan optimization. The objective function can be based solely on dose or it can use a radiobiological model. At this point, the dose-based approach is still widely used in practical optimization whereas biological models are often used conceptually. A given objective function can be optimized using many different optimization algorithms, such as iterative methods, simulated annealing, filtered backprojection, genetic algorithm, maximum likelihood approach, linear programming. The recent advance in the optimization of beam orientations in the configuration space will also be discussed. |