Influence of high pulse dose rate on biological effectiveness of laser accelerated electrons

The novel technology of particle acceleration based on high intensity lasers is characterised by ultra-short pulse particle beams and high pulse dose rate. Before a potential medical application such beams have to be characterized in terms of their radiobiological properties. Hence, systematic in vitro cell experiments were performed with laser accelerated electrons by using the Jena titanium:sapphire (JETI) laser system. As presented last year, residual H2AX/53BP1 foci and clonogenic survival for four human cell lines were therefore analysed. The dose response curves show a reduced radiobiological effectiveness for laser accelerated MeV electrons in comparison to the continuous 200 kVp X-rays. Conceivable reasons for the measured differences in the radiobiological effectiveness between both radiation qualities could be the difference in energy spectrum and mean dose rate as discuss in a separate contribution. The influence of the high pulse dose rate of the laser accelerated electron beam was investigated by using pulsed electron beams generated by the electron accelerator ELBE (Electron Linac for beams with high Brilliance and low Emittance) at Forschungszentrum Dresden-Rossendorf. The variable time structure of the ELBE electron beam allows pulsed irradiation as well as quasi-continuous irradiations, whereas the pulse doses are tunable over more than six orders of magnitude. Hence, ELBE can be used to mimic both ultra-short pulses of laser accelerated electrons as well as quasi-continuous electron beam as delivered by a conventional therapeutic linac. These two pulse regimes were applied in systematic in vitro cell studies by using monoenergetic electrons of 20 MeV. For a comparison the ELBE experiments were performed similar to the JETI experiments. Therefore, the same cell lines (FaDu, 184A1, additional HDF and F153) and the two biological endpoints (residual H2AX/53BP1 foci, clonogenic survival) were investigated. Preliminary results show no difference in the biological effectiveness between pulsed and quasi-continuous ELBE electrons as well as continuous X-rays.

The work was supported by the BMBF, grant no. 03ZIK445