Preparation of Animal Irradiation Experiments with Laser-Accelerated Protons and Pulsed High-Field Magnets

Particle therapy with energetic proton or heavy ion beams is considered as beneficial for a multitude of radiotherapy patients. The facility and operation costs as well as size and construction demands are considerably higher than for in-room radiotherapy systems based on generation of bremsstrahlung from an electron beam. Laser-acceleration has been considered a potential alternative for conventional accelerators like cyclotrons or synchrotrons and thus could provide a more compact and cost-efficient particle therapy solution in the future. The beam properties of laser accelerated beams strongly differ from the quasi-continuous beams generated by conventional accelerators. Laser accelerated beams exhibit fs to ps bunch length, carry up to 1013 particles with broad energy spectrum and are highly divergent. Furthermore, fluctuations of the said beam parameters on a shot-to-shot basis are inherent to the acceleration mechanism. Thus, special measures are required to make use of the novel particle source, especially considering the goal of a future medical application.

Pulsed high-field magnets, as also facilitated within the LIGHT collaboration, are a versatile and efficient way of shaping laser-accelerated beams both spatially and spectrally for application. Nevertheless, the bunches remain short and therefore intense, leading to high dose rates when stopped in matter. These dose rates make special demands for dosimetry and are a core aspect for radiobiological studies.

We performed experiments with the PW beam of the Draco laser to investigate the feasibility of worldwide first controlled volumetric tumour irradiations with laser-accelerated protons. Therefore, a setup of up to two solenoid magnets was used to efficiently capture and shape the beam, which was then analysed by means of spectrometer, electronic dosimeter and radiochromic film.

The talk will focus on reliable generation of homogeneous dose distributions lateral and in depth. Practical issues, like magnet repetition rate and stability, mean dose rate and future radiobiological challenges will be critically discussed. We will close with an outlook on the volumetric tumour irradiation study with specifically developed tumour model of LN229 cells, grown on the ears of nude mice. The radiobiological endpoint that will be investigated is the radiation induced tumour growth delay.