Laser-driven radiation: Biomarkers for molecular imaging of high dose-rate effects.

Recently developed short-pulsed laser sources garner high dose-rate beams such as energetic ions and electrons, x rays, and gamma rays. The biological effects of laser-generated ion beams observed in recent studies are different from those triggered by radiation generated using classical accelerators or sources, and this difference can be used to develop new strategies for cancer radiotherapy. High-power lasers can now deliver particles in doses of up to several Gy within nanoseconds. The fast interaction of laser-generated particles with cells alters cell viability via distinct molecular pathways compared to traditional, prolonged radiation exposure. The emerging consensus of recent literature is that the differences are due to the timescales on which reactive molecules are generated and persist, in various forms. Suitable molecular markers have to be adopted to monitor radiation effects, addressing relevant endogenous molecules that are accessible for investigation by noninvasive procedures and enable translation to clinical imaging. High sensitivity has to be attained for imaging molecular biomarkers in cells and in vivo to follow radiation-induced functional changes. Signal-enhanced MRI biomarkers enriched with stable magnetic nuclear isotopes can be used to monitor radiation effects, as demonstrated recently by the use of dynamic nuclear polarization (DNP) for biomolecular observations in vivo. In this context, nanoparticles can also be used as radiation enhancers or biomarker carriers. The radiobiology-relevant features of high dose-rate secondary radiation generated using high-power lasers and the importance of noninvasive biomarkers for real-time monitoring the biological effects of radiation early on during radiation pulse sequences are discussed.

Dose calculations in a cell monolayer for high-throughput irradiation with proton beams generated by PW lasers for space applications.

One of the specific properties of laser-driven radiation is a broadband energy spectrum, which is also a feature of the space radiation fields. This property can be used in materials science studies or radiobiology experiments to simulate the energy spectrum of space radiation exposures in a ground-based laboratory. However, the differences in effects between the higher dose rates of laser generated radiation and the lower dose rates of space radiation have to be investigated in separate, prior studies. A design for a high-throughput irradiation experiment and the associated Monte Carlo dose calculations for a broadband energy proton beam depositing energy in a cell monolayer is presented. Dose control and dose uniformity in the cell monolayer was achieved in the simulations using a variable thickness Ni attenuator. A set of target doses from 0.2 Gy to 4 Gy was obtained and dose uniformity was optimized to less than 4% variability. This work opens the possibility of single or multiple exposures, controllable, high-throughput irradiation experiments on biological samples or materials, using broadband energy particle beams generated by lasers, with relevance for space applications.