Berlin 2005 – scientific programme

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ST: Strahlen- und Medizinphysik

ST 5: Medizinphysik: Strahlentherapie mit Ionen II

ST 5.4: Fachvortrag

Tuesday, March 8, 2005, 12:00–12:15, TU HL1

Multiple field optimization of biologically effective dose — •Alexander Schmidt — GSI-Biophysik, Darmstadt

The GSI pilot project for cancer treatment uses a raster scan system which provides three-dimensional active dose shaping with ions. The scanner is controlled by a software (TRiP) which is capable to generate intensity modulated fields with several ten thousand raster points, each point corresponding to a specific beam position, energy and particle fluence. So far, it allows single-field optimization of physical and biological dose taking advantage of the local effect model (LEM). Optimization can be done using either the Newton algorithm or the method of conjugated gradients and requires calculation of the gradient of dose with respect to particle fluence of each raster point. Using a numerical method to obtain the total gradient we found out that the biological contribution is not negligible. It turned out that the calculation of biological dose and its gradient is vastly facilitated by a newly developed approximation of the LEM for low doses used in therapeutic fractions. Therefore multiple field optimization of biologically effective dose will soon be available for clinical usage.