Heidelberg 2006 – wissenschaftliches Programm

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ST: Strahlen- und Medizinphysik

ST 7: Strahlentherapie mit schnellen Ionen II

ST 7.5: Vortrag

Dienstag, 14. März 2006, 12:10–12:20, D

Optimization of biological effects in intensity modulated radiotherapy with charged particle beams — •Jan Wilkens and Uwe Oelfke — German Cancer Research Center (DKFZ), Department of Medical Physics in Radiation Oncology, Im Neuenheimer Feld 280, D-69120 Heidelberg

In tumour therapy with charged particle beams, the biological effect is not determined by the physical dose alone. The relative biological effectiveness (RBE) varies three-dimensionally in space due to different local particle spectra. For protons, these RBE variations are often disregarded in treatment planning, while they become essential for heavier ions. We investigate the potential impact of a variable RBE for scanning techniques in intensity modulated radiotherapy with particle beams and present strategies to include RBE variations into the inverse planning process.

The first approach is to employ the dose-averaged linear energy transfer (LET) to characterize the radiation field. In the optimization, LET constraints can be added to the conventional dose-based objective function to aim for homogeneous dose and LET in the planning target volume, while avoiding high values of dose or LET in organs at risk. A second, more general method is the direct optimization of the biological effect (i.e. RBE times dose) by using time-efficient models for the RBE to allow for simultaneous multifield optimization of the biological effect in a reasonable time. We demonstrate the successful application of these strategies for protons, and report on the ongoing extension to heavier ions like carbon.