## 2 Materials and Methods
### Experimental Set-Up
#### 2.2.2 Irradiation Configurations and Corresponding Dose per Pulse  
To obtain different dose per pulse values at the irradiation point, a combination of several plastic collimators of different lengths and diameters is used to change the total source to surface distance (SSD). Also, the applicator-to-detector distance (ADD) was varied to obtain different values of dose delivered per pulse. Such collimation system consists of polymethylmethacrylate (PMMA) cylindrical applicators that can be directly attached to the radiant head. Table 1 shows a summary of the configurations used and of the corresponding dose-per-pulse values, measured with RCFs and alanine detectors fixing a pulse duration of 2 \(\upmu\)s. A sketch of the experimental setup employed is shown in Figure 4a. In particular, commercial alanine pellet dosimeters (Gamma-Service, Produktbestrahlung, Radeberg, Germany) (diameter 4.80 \(\pm\) 0.04 mm, height 2.99 \(\pm\) 0.02 mm, weight 68.0 \(\pm\) 0.5 mg, density 1.26 \(\pm\) 0.02 g/cm\({}^{3}\) and mass ratio alanine/binder 0.96/0.04) [30] and radiochromic films EBT-XD type [31] were used to measure the dose delivered per pulse for each geometrical configuration used for the SiC irradiation. Both alanine detectors and RCFs were placed exactly in the same position of the SiC detector using a PMMA phantom as holder. Electron paramagnetic resonance (EPR) measurements were carried out to extract the dose from the irradiated alanine detectors at constant room temperature \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Applicator** & \multicolumn{2}{c}{**Applicator to**} & \multicolumn{2}{c}{**D/p RCF**} & \multicolumn{2}{c}{**D/p Alanine**} \\  & **Diameter [cm]** & **Detector Distance** & **[Gy]** & **[Gy]** \\ \hline \multirow{4}{*}{CONVENTIONAL} & 3.5 & 0 & 0.08 & 0.08 \\  & 4 & 0 & 0.03 & 0.02 \\  & 5 & 0 & 0.07 & 0.07 \\  & 12 & 0 & 0.08 & 0.08 \\  & 3.5 & 0 & 5.27 \(\pm\) 0.13 & 5.05 \(\pm\) 0.07 \\  & 4 & 0 & 4.59 \(\pm\) 0.11 & 4.42 \(\pm\) 0.05 \\  & 10 & 0 & 1.77 \(\pm\) 0.04 & 1.77 \(\pm\) 0.02 \\ FLASH & 10 & 28 & 1.04 \(\pm\) 0.02 & 1.08 \(\pm\) 0.01 \\  & 10 & 56 & 0.59 \(\pm\) 0.01 & 0.6 \(\pm\) 0.01 \\  & 12 & 111 & 0.21 \(\pm\) 0.01 & 0.22 \(\pm\) 0.01 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Irradiation conditions and correspondent dose per pulse for different applicators and distances from them for 9 MeV electron beams. As evident from the fist column, only for the 10 cm collimator different distances of the detectors from the final part of the applicator (ADD) were explored. Figure 4: (**a**) Sketch of the experimental setup indicating the source to distance surface (SSD) and the applicator to detector distance (ADD) that is reported in Table 2. (**b**) Dose transversal profiles measured with an RCF-EBT3 detector. using a spectrometer ELEXSYS E580 (Bruker, Karlsruhe, Germany) operating at the X-band [32]. A calibration in the dose range from 2.5 to 20 Gy was previously performed with conventional 6 MV photon beams produced by the ELEKTA Versa HD linear accelerator to convert the EPR signal in the absorbed dose. Radiochromic films EBT-XD type have been scanned using a flatbed scanner EPSON Expression 11000 XL (EPSON central branch Suwa, Japan), and the dose values for each configuration were obtained using FilmQA(tm) Pro v7 software (Ashland Inc., Wilmington, DE, USA). The batch was previously calibrated in a clinical LINAC (TrueBeam, Varian, Palo Alto, CA, USA) on an electron beam of 9 MeV and dose levels between 0 and 30 Gy, using the calibration procedure recommended by the manufacturer. All the measurements with the SiC, alanine and RCF detectors were performed at the maximum of the depth-dose distribution in water of the 9 MeV electron beam, obtained by placing a 13 mm thick solid water slab sandwiched between the applicator and the detector holder. For some cases, particularly for irradiations at FLASH regimes, one single pulse was necessary to get an acceptable dose in both the RCF and alanine detectors, according to their sensitivity.