## 2 Materials and Methods
### THz Spectroscopy  
Spectral measurements were performed in the 0.3-1.7 THz range using a THz TDS spectrometer T-SPEC (EKSPLA, Vilnius, Lithuania). This has a spectral resolution of 10 GHz, two delay lines, fast and slow, to provide real-time data acquisition with a 10 spectra/s speed, and a dynamic range of \(>\)90 dB at 0.4 THz [22; 58]. All measurements were carried out at a temperature of \(21\pm 1\)\({}^{\circ}\)C. Specially designed disposable cuvettes were produced from Watson material (Bestfilament, Tomsk, Russia) using a Designer X PRO 3D printer (PICASO 3D, Moscow, Russia) [58; 66]. This material has an acceptable transparency in the THz spectral range [67]. The thickness of the cuvette internal cavity was 0.5 mm. In the THz-TDS spectrometer, the THz wave was focused onto the cuvette center using parabolic mirrors (see Figure 2). A reference signal was recorded with an empty cuvette. Then,  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Day after Injection** & **The 7-th Day** & **The 14-th Day** & **The 21-st Day** \\  & **Group 1** & **Group 2** & **Group 3** \\ \hline Number of GBM samples & 5 & \(10\) & 7 \\ Number of CMI samples & 5 & 10 & 10 \\ \hline \hline \end{tabular}  
* Group 1 includes serum samples collected on the 7 th day, group 2, on the 14 th day, and group 3, on the 21 st day after injection, respectively.  
\end{table}
Table 2: Numbers of blood serum samples in each group *.  
without changing the position, the cuvette was filled with a serum sample (50 uL volume) using an automatic dispenser. An individual cuvette and dispenser tip were used for each sample analysis. The THz spectra measurement of a sample was conducted in six spatial points evenly distributed on the cuvette surface within a mesh grid were selected, with 0.1 mm steps in the horizontal and vertical directions. Averaging over 256 spectra was performed for each point of the 2D scans to reduce noise. The conversion of the signal from the time domain to the frequency domain was carried out using the Terravil TRS-16 software version 1.1.2.6 (TeraVil Ltd., Vilnius, Lithuania).  
In a transmission scheme, the THz spectrometer measures the complex transmission coefficient of a sample: \(\mathrm{T(v)}=\mathrm{E_{s}}\left(\mathrm{v}\right)/\mathrm{E_{r}}\left( \mathrm{v}\right)\), where \(\mathrm{E_{s}}\left(\mathrm{v}\right)\) is the complex electric field strength of the THz wave transmitted through the cuvette with a liquid sample, \(\mathrm{E_{r}}\left(\mathrm{v}\right)\) is the complex electric field strength of the THz wave transmitted through the empty cell, and \(\mathrm{v}\) is the frequency of the THz wave (see Figure 2). There is a quantitative relationship between the measured complex transmission coefficient \(\mathrm{T(v)}\) of a substance and its dielectric characteristics [34; 35; 36]. When the reference signal of different samples has a low dispersion, it makes sense to consider only the intensity of the signal on the output of the THz wave detector. This approach has been proven to work well in conjunction with machine learning methods [22; 58].  
As aforementioned, each serum sample was measured at six different spatial points 256 times, so 1536 THz spectra per sample were measured. After averaging at a spatial point, only 6 spectra remained. In total, according to the number of serum samples in each group (see Table 2), the data for GBM group 1 and CMI group 1 consisted of 30 spectra for every group; the data for GBM group 2 and CMI group 2 consisted of 60 spectra for every group; the data for GBM group 3 included 42 spectra; and the data for CMI group 3 included 60 spectra. The frequency domain mean intensity signal values and time domain spectra of the samples from the GBM and CMI groups are presented in Figure 3. The mean spectrum for the samples from the CMI group 1 has lower intensities compared to similar spectra from CMI groups 2 and 3.  
Figure 2: THz time-domain spectrometer used in the transmission mode.