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Laser-driven ion acceleration has been considered a potential alternative for conventional accelerators that may provide for a more compact and cost-efficient particle therapy solution in the future. The beam properties of laser-accelerated beams strongly differ from quasi-continuous beams from synchrotrons or cyclotrons. Laser-driven ion bunches are typically picoseconds short, yet carry up to 10^13 particles with a broad energy spectrum and high divergence. A current driving question is whether the highly intense pulsed ion beams obtain an equivalent biological effectiveness compared to quasi-continuous beams in the case that a living organism is irradiated. Therefore, a controlled small animal irradiation (LN229 glioblastoma cells on nude mouse ear) will be performed at the Dresden laser acceleration source Draco using an intense proton beam. The talk gives a general overview on laser-acceleration efforts in the context of translational medical research at HZDR and focuses on the experimental preparation and characterization of a proton beamline based on two pulsed high-field (20 T) solenoid magnets. The magnets match the pulsed nature of the particle source and provide for efficient beam capture, transport and field formation. Two challenging experimental tasks will be critically discussed: First, 25 MeV proton beam production at mean dose rates of the order of Gy/min with a high degree of reproducibility. And second, the generation of homogeneous lateral and depth dose distributions by means of the beam transport system.

The new particle acceleration by high intensity laser promises more compact and economic accelerators for cancer treatment. However, the resulting particle beam is pulsed with an ultra-short pulse-duration (~ ps) and has a large divergence and broad energy spectrum. Within the German joint research project “onCOOPtics” the clinical applicability of laser-driven proton beams is investigated including the development of a laser accelerator and suitable beam transport. The designed magnets are intended for a compact beam transport system (gantry) which efficiently transports proton pulses (≤ 220 MeV) from generation to treatment site. For this purpose the initially divergent proton beam is captured by a cylindrical electromagnet (solenoid), deflected by 45° dipole magnets and focussed by quadrupole magnets, while the energy window is selected by adjustable lead apertures. The implementation as short-pulsed (~ 1 ms) electromagnets allows to generate very high magnetic field strengths (up to 20 T) for short times, which enables the compact construction of both individual magnets and the whole gantry system. The pulse frequency of the magnets can be synchronized with that of the laser accelerator. The high field strengths demand high peak currents (up to 20 kA) and the resultant heating is dissipated by a cooling integrated into the magnets. The in-house developed pulsed magnets will enable a proton gantry 2-3 times smaller than those used in current clinical installations. Pulsed solenoids have been completely engineered and tested, and are routinely applied at laser particle accelerators. Two prototypes of a pulsed dipole and a first pulsed quadrupole were designed and manufactured, and their experimental characterization at the University Proton Therapy Dresden is in progress. Pulsed electromagnets are crucial components of a compact gantry and after their extensive individual testing they will be combined step-by-step and used at the laser proton accelerator.

Introduction: Compact laser-driven ion accelerators are a potential alternative to complex, large and expensive conventional accelerators. High-power short-pulse lasers, impinging on e.g. thin metal foils enable multi-MeV ion acceleration on µm length and ps time scale. The generated ion bunches (typically protons) show unique beam properties, like ultra-high pulse dose. Nevertheless, laser accelerators still require substantial development in reliable beam generation and transport. We present first experimental results on a beamline prototype based on high-field magnet technology specifically designed for capture and transport of laser-accelerated particles. Material and methods: Since the mid-1950s, pulsed high-field magnets serve as versatile research tools for solid state physics and material research. Recently developed pulsed magnet technology, specifically designed to meet the demands of laser acceleration [1], open up new research opportunities: We present a pulsed solenoid for effective collection and focusing of laser-accelerated ions which could function as a first component in a laser-driven gantry system [2]; furthermore, we present a dipole magnet for beam deflection and energy dispersion. The magnets were combined to form a first, pulsed high-field beamline and are powered by portable pulse. Characterization of both magnets has been carried out using a 10 MeV proton beam from a conventional Tandetron accelerator at Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The transported beam was detected by means of radiochromic film and scintillator. Result: The transport experiments clearly show the functionality of both magnets: The solenoid focuses the large, divergent ion beam to a millimeter-sized spot showing no aberration. The dipole deflects the protons by a 45° angle and can be used as energy selection device via energy dispersion. For the several 10 µs long proton bunches no effect of the time structure of the magnetic pulse (~ several 100 µs) was observed thus making the magnets well suited for even shorter, laser-driven ion bunches. The beam position accuracy, after passing the beamline, was measured to be of the same order as the beam position fluctuations itself, showing the precision of the installed beamline. The maximum magnetic field strength achieved was 20 T for the solenoid and 5 T for the dipole. For operation at higher proton energies, i.e. above 200 MeV, an increase by a factor of only 1.5 – 2 is requested. Summary: Our experimental results show that compact high-field magnets can be used to precisely guide charged particle bunches. The pulsed nature of laser-accelerated particles is matched by the magnet technology. The maximum field strengths reached are sufficient for experiments with protons of several 10 MeV kinetic energy. For clinically relevant energies above 200 MeV, however, a slight increase is required. Experimental studies at a laser-accelerator are scheduled. References [1] T. Burris-Mog, et al., Laser accelerated protons captured and transported by a pulse power solenoid, PRSTAB 14, 121301 (2011) [2] U. Masood, et al., A compact solution for ion beam therapy with laser accelerated protons, Appl. Phys. B 117, 41 (2014)

Introduction During the last years, the new technology of laser based particle acceleration was developed at such a rate that medical application for cancer therapy becomes conceivable. Promising more compact and economic accelerators, the laser technology however generates intense ultra-short (~ ps) pulsed proton beams with large divergence and broad energy spectrum. Within the German joint research project “onCOOPtics” the clinical applicability of such pulsed proton beams is investigated including the development of a laser accelerator and a suitable beam transport. Methods A compact beam transport system was designed enabling an efficient transport of proton pulses from generation to treatment site. The initially divergent proton beam is captured by a cylindrical electromagnet (solenoid), deflected by 45° dipole magnets and formed by quadrupole magnets, whereas the spectrum is shaped by adaptable lead apertures. For realization, electromagnetic dipoles with magnetic fields of up to 10 T are required to deflect up to 220 MeV protons. These field strengths are achieved by in-house developed non-ferrous dipoles that consist of 80 copper coils in 12 layers and are operated at peak currents of up to 20 kA. To handle the high currents and the generated heat the dipoles are externally cooled and operated in 1 ms short pulses synchronized with the laser repetition frequency. Results The prototype of a short-pulsed electromagnetic dipole magnet was designed and manufactured. Results of the experimental characterization and first performance tests at a conventional Tandem accelerator are under way. Conclusion Pulsed electromagnetic dipoles as crucial components of a compact beam line for laser-accelerated protons are engineered. Following validation of their suitability at a conventional accelerator the dipoles will be implemented and further tested at a laser accelerator. Together with improvement of the dipole the design of quadrupoles will start.

Proton beams by their well-confined energy-loss in matter are a promising tool for the improvement of radiotherapy of cancer and are currently under intense medical investigation. Wider clinical use, however, is limited by the complexity and expense of current proton and ion accelerators. Compact laser driven proton therapy accelerators are discussed as a promising alternative, yet require substantial development in reliable beam generation and transport, but also in dosimetric protocols as well as validation in radiobiological studies. In our talk, we will present the first direct and dose controlled comparison of the radiobiological effectiveness (RBE) of intense proton pulses from a laser driven accelerator with conventionally generated continuous proton beams, showing no dependence of the RBE on the different beam properties [1]. Controlled dose delivery, precisely online and offline monitored for each of the ~ 4000 proton pulses, resulted in an unprecedented relative dose uncertainty of below 10%, using approaches scalable to radiotherapy applications. In parallel to the development of laser driven proton therapy accelerators, an advancement in instrumentation for laser driven protons is essential. Most importantly, these new diagnostic tools need to speedwise match the repetition rates of state-of-the-art high power laser systems and need to be adapted to the harsh plasma environment of laser based accelerators, not neglecting their fitment to the properties of laser accelerated proton pulses such as the high flux and the broad energy spectrum. We will present three types of scintillator-based detectors, all being optimized for specific stages of the experimental chain: a one-dimensional space- and energy-resolved detector for online spectral stability control of the acceleration performance [2], a two-dimensional space- and energy-resolved detector for source characterization measurements, and a three-dimensional detector for precise dose verification in a water-equivalent medium with regards to medical quality assurance [3]. [1] K. Zeil, et al.: Dose-controlled irradiation of cancer cells with laser-accelerated proton pulses, Appl. Phys. B (2012) [2] J. Metzkes, et al.: A scintillator-based online detector for the angularly resolved measurement of laser-accelerated proton spectra, Review of Scientific Instruments, Rev. Sci. Instrum. 83, 123301 (2012) [3] F. Kroll, et al.: Preliminary investigations on the determination of three-dimensional dose distributions using scintillator blocks and optical tomography, Med. Phys. 40, 082104 (2013)

An Integrated DOsimetry and Cell Irradiation System (IDOCIS) with laser-accelerated proton beams was developed, characterized, calibrated and successfully used for systematic in vitro experiments. Due to the broad exponentially shaped energy spectrum, the low energy range of the protons (< 20 MeV) and the high pulse dose, the absolute dosimetry for this beam quality is challenging. Therefore, a dedicated Faraday cup is used as an energy and dose rate independent absolute dosimeter that has been calibrated consistently with three independent methods. A transmission ionization chamber providing online relative dose information is cross-calibrated against the Faraday cup. Providing both online and absolute dose information the IDOCIS allows for quantitative dosimetric and radiobiological studies at current low-energy laser-accelerated proton beams. Finally, first dosimetric characterizations of a laser-accelerated proton beam with the IDOCIS are presented.

Background: The novel technology of particle acceleration based on high intensity laser systems promises proton therapy accelerators of compact size and reasonable costs. Laser acceleration results in ultra-short pulsed (~100 fs) particle beams with very high pulse dose-rate (in the order of 1012[for full text, please go to the a.m. URL], PTCOG 48; Meeting of the Particle Therapy Co-Operative Group