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ST: Strahlen- und Medizinphysik

ST 11: Verbesserung der Bestrahlungsplanung

ST 11.3: Talk

Tuesday, March 14, 2006, 17:10–17:20, D

Probabilistic treatment planning to incorporate organ motion into IMRT optimization — •Jan Unkelbach and Uwe Oelfke — Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany

We present an off-line approach to incorporate organ motion into the treatment plan optimization for fractionated intensity modulated radiotherapy (IMRT). Organ movements are described in terms of a mathematical model that represents the basis of the treatment plan optimization process. The motion model contains random variables in order to describe the stochastic nature of organ movements. As a consequence, the predicted dose distribution in the patient has to be considered as a random variable aswell. It is characterized by an expectation value of the dose and its variance. For treatment plan optimization incorporating the motion model, the expectation value of a quadratic cost function is minimized, which can be expressed as the sum of the variance of the dose and the quadratic difference of expected and prescribed dose. The resulting treatment plans show a reduction of the dose in regions where tumor tissue is located only rarely. This is compensated for by delivering a higher dose to neighboring regions that are mostly occupied by tumor tissue. Due to the organ movements during the course of treatment, a widely homogeneous cumulative dose distribution is delivered to the tumor. The method potentially allows for a better sparing of healthy tissues from dose burden compared to the standard safety margin approach.