Simulation and visualization of dose uncertainties due to interfractional organ motion

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Abstract
In this paper, we deal with the effects of interfractional organ motion during radiation therapy. We consider two problems: first, treatment plan evaluation in the presence of motion, and second, the incorporation of organ motion into IMRT optimization. Concerning treatment plan evaluation, we face the problem that the delivered dose cannot be predicted with certainty at the time of treatment planning but is associated with uncertainties. We present a method to simulate stochastic properties of the dose distribution. This provides the treatment planner with information about motion-related risks of different plans and may support the decision for or against a treatment plan. This information includes the display of probabilities of individual voxels to receive doses from a therapeutical interval or above critical levels, as well as a diagram that shows the variability of the dose volume histogram. Concerning the incorporation of organ motion into IMRT planning, we further analyse the approach of inverse planning based on probability distributions of possible patient geometries. We consider three different sources of uncertainty, namely uncertainty about the amplitude of motion, a systematic error and a random error. We analyse the impact of these sources of uncertainty on the optimized treatment plans for prostate cancer.