Two approaches for calculation of the absorbed dose in the presence of target motion --- a comparative study based on patient data

In the course of scanned carbon ion beam cancer treatment at GSI, 437 patients were successfully treated at sites that could be immobilized. With the upcoming facilities in Heidelberg, Marburg, and Kiel one major task is the expansion of the rasterscan technique [1] to moving tumors, e.g. lung cancer. This requires an extension of the treatment planning software TRiP [2] by 4D functionalities. In a first step, TRiP was extended by the possibility to calculate the absorbed dose in the presence of motion (linear method (LM)) [3, 4]. Recently, calculation of the RBEweighted dose was implemented in TRiP using a different calculation scheme. As part of the new approach, that is capable of taking nonlinear dose dependencies into account and therefore referred to as non-linear method (NLM), the absorbed dose is determined in a different way than in the LM but should lead to the same results. LM and the NLM were compared based on 4D data from three lung-cancer patients.