We report on the conceptual design of a 2 μm, ultrashort pulse laser system including power amplification based [1] on Tm-doped gain medium. We consider ceramic [2] Tm:Lu2O3 with a direct diode-pumping architectures to develop a solid-state laser technology for high-efficiency, high repetition rate and ultra-short pulse laser, with high peak power and kWscale average power.. A CW pumping (duty cycle of the diodes 100%) and a multi-pulse extraction mode [3] scheme are considered with a multipass scheme with thin disk Tm:Lu2O3 doped at 4% and with lateral (edge) [5] pumping (EPDL). Here we show the preliminary results of the modelling of a two-stage amplifier operating at a repetition rate of 1 kHz, output energy of <500mJ, with a maximum fluence of about 1.5 J/cm2 for the first stage and of about 2 J/cm2 for the second stage. The optical model of the two-stages is based on a multi-pass configuration and designed for a gain of 50x and 12x respectively. Each stage consists of two gain media in active mirror configuration. This conceptual design represents the best balance between constructive complexity and efficiency in terms of energy gain.
The direct use of so-called Very High Energy Electrons for radiotherapy is currently deserving a renewed and growing attention. This is mostly due to the recent emergence of the so-called FLASH effect in radiobiology [1], consisting in a surprising reduction of adverse effects on healthy tissue by ionizing radiation when dose delivery occurs at very high average dose rates (greater than a few tens of Gy/s). In order for a real clinical translation of this new protocol in the clinical practice, the development of novel kind of ionizing radiation sources featuring such very high dose rates, which are basically hindered by the relatively low Bremsstrahlung conversion efficiency in current machines, is considered as an essential step. With this respect, laser-driven accelerators of Very High Energy Electron (VHEE) beams, with energy in the range 100-250 MeV, are regarded as one of the most promising tool [2]. Furthermore, both early studies, dating back to 1990s, and more recent works suggest that an improved dose deposition pattern can be expected from electron beams, as compared to photon beams, when the very high energy region is reached.
In this talk, we report on a recent experiment aimed at assessing dose deposition for deep seated tumors using advanced irradiation schemes, typical of current radiotherapy protocols, with an existing laser-driven VHEE source [3]. In particular, our measurements showed control of localized dose deposition and modulation, suitable to target a volume at depths in the range from 5 to 10 cm with mm resolution. Based on this experimental findings and on further numerical simulations, we also discuss the features and potentialities of laser-driven VHEE sources for radiobiology experiments aimed at deepening the understanding of the mechanisms underpinning the FLASH effect. The main requirements and the perspectives for a longer term translation of an electron-based radiotherapy into the real clinical practice will be also addressed.
[1] M.-C. Vozenin et al., Biological Benefits of Ultra-high Dose Rate FLASH Radiotherapy: Sleeping Beauty Awoken, Clin. Oncol. 31 (2019), 407
[2] A. Giulietti (Eds), Laser-Driven Particle Acceleration Towards Radiobiology and Medicine, Springer (2016)
[3] L. Labate et al., Toward an effective use of laser‐driven very high energy electrons for radiotherapy: Feasibility assessment of multi‐field and intensity modulation irradiation schemes, Sci. Rep. 10 (2020), 17307
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