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Purpose: The use of laser accelerators in radiation therapy can perhaps increase the low number of proton and ion therapy facilities in some years due to the low investment costs and small size. The laser-based acceleration technology leads to a very high peak dose rate of about 10{sup 11} Gy/s. A first dosimetric task is the evaluation of dose rate dependence of clinical dosimeters and other detectors. Methods: The measurements were done at ELBE, a superconductive linear electron accelerator which generates electron pulses with 5 ps length at 20 MeV. The different dose rates are reached by adjusting the number of electrons in one beam pulse. Three clinical dosimeters (TLD, OSL, and EBT radiochromic films) were irradiated with four different dose rates and nearly the same dose. A faraday cup, an integrating current transformer, and an ionization chamber were used to control the particle flux on the dosimeters. Furthermore two diamond detectors were tested. Results: The dosimeters are dose rate independent up to 410{sup 9} Gy/s within 2% (OSL and TLD) and up to 1510{sup 9} Gy/s within 5% (EBT films). The diamond detectors show strong dose rate dependence. Conclusions: TLD, OSL dosimeters, and EBT films are suitable for pulsedmore » beams with a very high pulse dose rate like laser accelerated particle beams.« less

Purpose: In recent years, laser-based acceleration of charged particles has rapidly progressed and medical applications, e.g., in radiotherapy, might become feasible in the coming decade. Requirements are monoenergetic particle beams with long-term stable and reproducible properties as well as sufficient particle intensities and a controlled delivery of prescribed doses at the treatment site. Although conventional and laser-based particle accelerators will administer the same dose to the patient, their different time structures could result in different radiobiological properties. Therefore, the biological response to the ultrashort pulse durations and the resulting high peak dose rates of these particle beams have to be investigated. The technical prerequisites, i.e., a suitable cellirradiation setup and the precise dosimetric characterization of a laser-based particle accelerator, have to be realized in order to prepare systematic cellirradiation experiments. Methods: The Jena titanium:sapphire laser system (JETI) was customized in preparation for cellirradiation experiments with laser-accelerated electrons. The delivered electron beam was optimized with regard to its spectrum, diameter, dose rate, and dose homogeneity. A custom-designed beam and dose monitoring system, consisting of a Roos ionization chamber, a Faraday cup, and EBT-1 dosimetry films, enables real-time monitoring of irradiation experiments and precise determination of the dose delivered to the cells. Finally, as proof-of-principle experiment cell samples were irradiated using this setup. Results: Laser-accelerated electron beams, appropriate forin vitro radiobiological experiments, were generated with a laser shot frequency of 2.5 Hz and a pulse length of 80 fs. After laser acceleration in the helium gas jet, the electrons were filtered by a magnet, released from the vacuum target chamber, and propagated in air for a distance of 220 mm. Within this distance a lead collimator (aperture of 35 mm) was introduced, leading, along with the optimized setup, to a beam diameter of 35 mm, sufficient for the irradiation of common cell culture vessels. The corresponding maximum dose inhomogeneity over the beam spot was less than 10% for all irradiated samples. At cell position, the electrons posses a mean kinetic energy of 13.6 MeV, a bunch length of about 5 ps (FWHM), and a mean pulse dose of 1.6 mGy/bunch. Cross correlations show clear linear dependencies for the online recorded accumulated bunch charges, pulse doses, and pulse numbers on absolute doses determined with EBT-1 films. Hence, the established monitoring system is suitable for beam control and a dedicated dose delivery. Additionally, reasonable day-to-day stable and reproducible properties of the electron beam were achieved. Conclusions: Basic technical prerequisites for future cellirradiation experiments with ultrashort pulsed laser-accelerated electrons were established at the JETI laser system. The implemented online control system is suitable to compensate beam intensity fluctuations and the achieved accuracy of dose delivery to the cells is sufficient for radiobiological cell experiments. Hence, systematicin vitrocellirradiation experiments can be performed, being the first step toward clinical application of laser-accelerated particles. Further steps, including the transfer of the established methods to experiments on higher biological systems or to other laser-based particle accelerators, will be prepared.

Purpose: Before the novel technology of laser‐based particle acceleration can be used for clinical applications, several requirements have to be fulfilled. These are the supply of stable and reliable particle beams with reproducible properties, sufficient particle intensity and useable energy spectra. Additionally, a precise dosedelivery in an appropriate time and the exposure of a desired irradiation field are needed. Beside these demands, consequences on dosimetry as well as on the radiobiological effect have to be investigated for ultra‐short pulsed laser‐accelerated particle beams.Method and Materials: The joint project onCOOPtics, an interdisciplinary and multicenter institution focusing on the development of a laser particle accelerator for radiation oncology, is introduced. The worldwide first systematic in vitroirradiations with laser‐accelerated electrons performed with the JeTi laser system will be presented focusing on the experimental setup, practical experiences and on dosimetric and radiobiological results. In a next step, cell irradiation experiments with laser‐accelerated protons have been prepared. Therefore, a dedicated dosimetric system was developed. It is integrated into a device that can be installed at different laser and conventional accelerators and serves also as cell or animal irradiation device. Results: A laser accelerator was successfully optimized for systematic radiobiological experiments performed over 3 months. No significant differences between laser‐accelerated and conventional 6 MeV electron beams were found. An integrated dosimetry and cell irradiation device for systematic in vitro and in vivo experiments with laser‐accelerated protons was developed, characterized, calibrated and successfully tested with both continuous and pulsed protonbeams. Cell irradiations with protons have been started. Conclusion: Laser accelerators can be used for radiobiological experiments, meeting all necessary requirements like homogeneity, stability and precise dosedelivery. Nevertheless, before fulfilling the much higher requirements for clinical application, several improvements concerning i.e. proton energy, spectral shaping and patient safety are necessary. Supported by BMBF (03ZIK445).