Heidelberg 2006 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

ST: Strahlen- und Medizinphysik

ST 11: Verbesserung der Bestrahlungsplanung

ST 11.9: Talk

Tuesday, March 14, 2006, 18:10–18:20, D

Towards risk adapted inverse planning for protons: Avoiding risks due to lateral tissue inhomogeneities — •Daniel Pflugfelder, Jan Wilkens, Hanitra Szymanowski, and Uwe Oelfke — DKFZ Heidelberg

Treatment planning of intensity modulated radiotherapy with proton beams leads to a highly degenerated space of solutions. Due to the huge number of degrees of freedom it is possible to find many solutions which have a dose distribution equivalent to the optimal solution. We use this fact to search for plans which not only have an acceptable dose distribution, but are also safe to deliver. As a first risk factor we focused on lateral tissue inhomogeneities, and introduced a homogeneity number H to quantify these inhomogeneities for each beamspot. Additionally we calculate the dose calculation error of each beamspot by comparing the commonly used pencil beam algorithm to the gold standard, namely Monte Carlo simulations. A clear correlation between the dose calculation error and the homogeneity number can be seen. A correlation between H and the sensitivity of a beamspot to setup errors is also observed. Since H can be calculated very fast we conclude that it is a useful tool to rate individual beamspots. This information can be used to exclude or penalize potentially dangerous beamspots in the optimization, or simply to recalculate individual beamspots by a more accurate but computationally more demanding algorithm like finesampling of the pencil beam or Monte Carlo simulations.