Three-dimensional BANG (TM) gel dosimetry in conformal carbon ion radiotherapy

In this study we applied BANG(TM) polymer-gel dosimetry using magnetic reso nance imaging (MRI) to densely ionizing radiation such as carbon ion beams. BANGTM polymer gels were irradiated with a quadratic field of monoenergeti c C-12 ions at different beam energies in the range of 135 MeV u(-1) to 410 MeV u(-1). They were irradiated at the radiotherapy facility of the GSI, D armstadt, Germany. Our object was to examine the saturation effect for dens ely ionizing radiation that occurs at high values of linear energy transfer (LET). The examination yielded the first effectiveness values that will be discussed in the following sections. A solid sphere and a hollow sphere we re both irradiated with a horizontal pencil beam from the raster scanning f acility at energies of 268 MeV u(-1) (solid sphere) and 304 MeV u(-1) (holl ow sphere) respectively. MR dosimetry measurements were compared with data from a planning system. As far as quality is concerned. there is good agree ment between the measured dose distributions of both samples and the dose m aps from the planning software. The measured MR signals cannot be converted into absolute dose, since the relative efficiency is still unknown for mix ed radiation fields of primary carbon ions and it is known only to a limite d extent for nuclear fragments with different energies from highly energeti c photon radiation. Model calculations are in progress in order to facilita te conversions of measured MR signals into dose.