OER VS. LET for Treatment Planning of Particle Beams - A First Database with Different O2 Conditions -

A feature of many solid aggressive and invasive tumors is the presence of high radio/chemio-resistant hypoxic regions. It has been demonstrated that the oxygen lack increases the tumor radio-resistance, an effect quantified by the oxygen enhancement ratio (OER). It is also well known that this radio-resistance depends on the radiation quality.With heavy ion irradiation, the high linear energy transfer (LET), can reduce drastically the OER, from a value close to 3, which occurs with X-rays, down to a value close to 1.Many studies have been done to calculate the OER for the X-Ray irradiation at different oxygenation conditions and many others have been performed for heavy ions in complete anoxia, 0% oxygen. However, no ion beam measurements have been done for intermediate oxygen concentrations, the most common in tumor, physioxia. In our work we present the first dataset of OER as a function of oxygen concentration and linear energy transfer (LET) using Chinese hamster ovary (CHO) cells irradiated with different ions at different facilities - Helmholtzzentrum for heavy ion research (GSI) Heidelberger Ionenstrahl Therapie (HIT) in Germany and National Institute of Radiological Sciences (NIRS) Japan. These measurements supported the development of a model, which has been introduced in the treatment planning system (TPS) TRiP98. In this way, it was possible to predict the cell survival in an extended target, simulating a tridimensional tumor with heterogeneous oxygenation both with a non-adapted and an adapted treatment planning. The experimental survival fraction values agree with the calculated simulation both in the entrance channel and in the target. Our model will be used to create an adaptive treatment planning for particle therapy, to allow performing OER driven optimization for hypoxic heterogeneous tumors. ; Space Radiation and Heavy Ions on Therapy Symposium 2015