PID2023-148992OB-C21

«High dose rate, high throughput in-vitro proton irradiation at the VEGA laser facility», Generación de Conocimiento 2023, Agencia Estatal de Investigación, PID2023-148992OB-C21. Collaborators: i3M (CSIC), Centro de Láseres Pulsados (CLPU, Salamanca).

Experimental studies of radiobiological effects of protons are realized at dedicated, clinical or non-clinical facilities. Among these, particle accelerators based on ultra-intense laser pulses stand out. In a recent project the i3M-CSIC applicant group has developed an experimental setup for the controlled irradiation of living cells. This device enables the application of ultra-short, mono-energetic pulses of protons to cell cultures prepared and analyzed by experts in clinical and preclinical research. In October 2023 this setup was used in a pilot experiment at the Spanish Pulsed Laser Center (CLPU, Salamanca), in close collaboration with the applicant of subproject 2 and with other, external groups. The analysis of a colony formation assay of human lung adenocarcinoma (A549) cells has been accomplished by the time of this proposal; further analyses of biological endpoints and the physical performance of the setup are ongoing.

The main objective of the present subproject 1 is the realization of cell culture irradiation studies at much higher dose rates and sample throughput than before. In our pilot experiment at the VEGA-3 laser of CLPU the dose per laser shot was of 0.1 Gy. Between 30 and 80 shots had to be realized for each of the samples to accumulate a clinically relevant dose of 3-8 Gy. We will now optimize several details to increase the single-shot dose by a factor 20-50. This will be achieved at the VEGA-2 laser line where the geometry of the arrangement will be much more compact to avoid proton beam broadening in dead space. By use of a laser focussing optics with short focal length we expect to obtain similar (or even higher) proton energies and particle fluences than at VEGA-3, at less laser energy on target and, by consequence, reduced generation of electromagnetic pulses interfering with electronic devices. An additional factor 10 gain in dose rate will be possible by exploiting the maximum VEGA-2 repetition rate of 10 Hz. This means that mean dose rates of several Gy/s will become feasible; even the FLASH regime (>40 Gy/s) will come into reach.

The high-dose rate capacity of our revised setup will have another, important implication. The investigation of radiation induced cell damage and repair effects may require the irradiation of several tens of cell cultures depending on the biological endpoint. The entire set of samples should be treated on the same day, ideally within 2-3 hours to the most. With the envisaged, high dose rates at VEGA-2 the irradiation time per sample will be significantly reduced, allowing for increased throughput.

The experiments with laser-accelerated protons at VEGA-2 will be complemented by likewise studies with different radiation fields such as clinical (MeV) x-rays, low-energy (<100 keV) x-rays, and continuous proton beams at radiofrequency accelerators. We will ensure the comparability of the cellular effects by applying the same protocols for sample preparation and analysis. These will be elaborated and shared between all our local partners.