Biophysical research

Biophysical research started 1975 in parallel to the other research projects at GSI using heavy ion beams from the low energy beam line at the UNILAC and since 1990 also from the heavy ion synchrotron SIS.

From the beginning, the major topic was the investigation of the differences in biological action of heavy ion radiation and photon radiation exploiting the broad range of particle species and beam energies available at the GSI accelerator facilities: in general, an increased relative biological effectiveness (RBE) is found for charged particles compared to X-rays. However, for low energies the effectiveness decreases.

Consequently, the basic physical interaction like the energy deposition process and the electron emission became a topic of GSI research. The following biochemical processes leading to DNA damage and its repair can be visualized and studied by microscopic analysis using immfluorescent dyes bound to the different proteins involved in the recognition and repair processes. A powerful tool for these studies is the microbeam facility where single ions can be directed to cell compartments with an accuracy of approx. 1 μm. DNA damage at higher order of organisation can be studied in the expression of various types of chromosomal abnormalities. These experimental studies are complemented by the development of biophysical models.

For the application of heavy ion radiation in tumor therapy, the physical properties of ion beams have to be known with high precision. Many experiments are thus dedicated to study depth-dose distributions (so called Bragg curves), beam fragmentation, and neutron production. In addition to physical dosimetry, tools of biological dosimetry have been developed where treatment plans are verified in water phantoms with high spatial resolution by means of cell survival experiments. Furthermore, technical developments have contributed significantly to the success of the heavy ion therapy project: a new beam delivery system (the 'rasterscan' system) allows an intensity modulated particle treatment IMPT of the tumors without unnecessary dose deposition in surrounding normal tissues.

In addition, aspects of radiation protection are part of the experimental program. For example, electronic equipment from satellites is tested for radiation hardness, and neutron production in shielding material is measured. In space flights, high flashes are induced by the direct excitation of nerves by the heavy particles of the cosmic radiation. In this framework, animal experiments are performed as well as in vitro studies.