# Dosimetric Optimization of a Laser-Driven Irradiation Facility Using the G4-ELIMED Application
## 4 Discussion  
The presented simulations used a realistic (experimental) high-power laser-accelerated proton source term as input for modeling its selection and transport. A relatively low kinetic energy window (centered at 20 MeV) was considered of interest for the pilot, invitro radiobiology experiments at the ELIMAIA-ELIMED beamline. The use of the Energy Selection System (ESS) as an active energy modulator was proven to be feasible, but it showed the drawback related to the need to re-positioning the four PMQs to transport protons with different kinetic energies. However, these changes in the configuration of the collecting system (PMQs) are not expected to drastically increase the overall irradiation time (approximately 2 additional minutes), thus it would enable radiobiological irradiations in a reasonable amount of time (around 6 min). Moreover, it is expected that at higher energies (around 60 MeV, i.e., already laying in the clinical window) a single configuration of the beam focusing system would allow a more efficient transport and injection into the ESS, both for low and high proton energies based on the presence of given resonances [38], thus potentially shortening the overall sample irradiation time required to create a clinical SOBP. Finally, it is noteworthy that the experimental source term (laser-driven proton source) can be improved in terms of total proton flux, thus enhancing the final dose delivered onto the user sample.  
The numerical results presented are promising in terms of final particle beam properties and demonstrate to fulfill the quality requirements for clinical applications. Furthermore, it was shown that unwanted plasma ion species, such as carbon ions, are properly filtered out in the ELIMED beamline. Thus, once the experimental characterization of the proton source at ELIMAIA will be carried out, the ELIMED beamline can be fine-tuned based on the actual initial proton beam spectral and spatial features at the source, and ultimately be optimized for pilot radiobiological tests with ultrahigh dose-rate, ultrashort laser-accelerated beams.  
Figure 6: Energy spectra of carbon ions along ELIMED beamline: (**a**) Absolute energy spectra of C6+, ions at different points along the ELIMED beamline; (**b**) Absolute energy spectra of protons (magenta line), C4+ (black line), C5+ (blue line) and C6+ (red line) ions after the ESS. The spectra of C1+, C2+, and C3+ beams are not included because they are fully filtered before the end of the ESS.  
**Author Contributions:** The paper's initial idea was proposed by [PERSON], [PERSON], [PERSON] and [PERSON]. The conceptualization is by [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON]; the software work and analysis were performed by [PERSON]; Supervision by [PERSON] and [PERSON]. The original draft preparation was by [PERSON], [PERSON] and [PERSON] and the review and editing were performed by [PERSON], [PERSON], [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by INFN in the framework of the Interdisciplinary Committee and by the MC-INFN and ELIMED projects; it was also funded by the Ministry of Education, Youth, and Sports of the Czech Republic through the project \"Advanced Research Using High-Intensity Laser-Produced Photons and Particles\" (CZ.02.1.010.00.016_019000789).  
**Data Availability Statement:** Data are available from the corresponding authors upon reasonable request.  
**Conflicts of Interest:** The authors declare no conflict of interest.