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Modeling and Prediction of Abdominal Tumor Motion. Haobing Wang Department of Computer Science May 9 th , 2003. Project Outline. Topic and Goal Background and Motivation Methods Experiments Analysis Future Work. Topic and Goal. - PowerPoint PPT Presentation
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Modeling and Prediction of Abdominal Tumor Motion
Haobing Wang
Department of Computer Science
May 9th, 2003
Project Outline Topic and Goal Background and Motivation Methods Experiments Analysis Future Work
Topic and Goal Facilitate real-time tracking of the tumor
motion during radiotherapy and allow for for precise delivery of radiation dose to mobile tumors.
Find methods to model and predict abdominal tumor motion.
Background and Motivation Tumor position is modeled by tracking
surgically implanted clips surrounding the tumor.
The radiation beam has mechanical latency.
Template Matching Using DHMM DHMM: Deformable Hidden Markov
Model Given a pattern template, recognizing the
pattern in a new time series, allowing flexible deformation of time.
Template Matching Using DHMM Generalize the standard constant model and
allow each state to generate data in the form of a regression curve.
K-state segmental HMM each state of which corresponds to one segment in the piecewise linear representation of the template.
Template Matching Using DHMM Use a sinusoid as template
The DHMM automatically find the period whose shape is similar to a sinusoid. Then the sequence is found is used as the prediction of the next breathing period.
Experiments of DHMM Method
0 100 200 300 400 500
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Experiments of DHMM MethodPrediction of 100 frames
Analysis of DHMM Method
Average error and error variance is greater than 1 millimeter.
Although the computation time for each clip is around 5 minutes, it’s still cannot be done on-line.
Prediction by Curve Fitting A least square method to fit the data points
to a third order polynomial function: f(x) = b0 + b1x + b2x
2 + b3x3 . The set of
coefficients [bn] can be found by
minimizing the sum:
2
1
33
2210 )]([
N
kkkkk xbxbxbby
Examples of Curve Fitting
Prediction by Curve Fitting Suppose S is the shape function which
describes the trajectory of a single breathing period, and (t) is a weighing function. I use as a decay factor. So S(t) can be computed by:
Sk = f(t) + (1-tSk-1
Experiments of Curve FittingBob (clip 2)
Experiments of Curve FittingGary (clip 0)
Experiments of Curve FittingResults of predicting approximately 550 frames on average
Experiments of Curve FittingResults of predicting 100 frames
Comparison of Four MethodsPredicting 100 frames
Analysis of Curve Fitting
Gives better result. Average error is the best among the four methods, and error variation is the second to the best.
Computation is fast. Can be done on-line.
Future Work
Adjustment of duration of each breathing period.
Improvement of the performance of the clip tracker and patients’ breathing pattern.
Future Work