## 2 Materials and Methods
### Microdsimetric Measurements Using TEPC
#### 2.2.3 Analysis of Microdosimetric Spectra and Dose Components  
The analysis of microdosimetric spectra, illustrating dose distributions of lineal energy, was conducted based on the following considerations. In the case of indirectly ionizing radiation, such as photons and neutrons, energy deposition within the SV occurs primarily via secondary charged particles generated in the A-150 cathode, while the number of secondary charged particles generated in the gas is very small due the low density of the interacting medium. One example of such secondary particles is Compton electrons, contributing to events with small lineal energy, typically below 20 keV/\(\upmu\)m, in the \"photon-component\" region (refer to Figure 3). The region of \(y\)-values greater than 20 keV/\(\upmu\)m is produced mainly by protons and other recoil ions. These particles have higher stopping powers than electrons; therefore, they deposit greater amounts of energy within the SV. This region of the spectrum above 20 keV/\(\upmu\)m is referred to as the \"neutron component\" and encompasses events arising from fast, epithermal, and thermal neutron reactions, including the contribution from BNC events when \({}^{10}\)B atoms are present. The BNC component occupies the spectrum region ranging from 50 to 800 keV/\(\upmu\)m.  
To determine the three main dose components, namely \(D_{\text{ph}}\) (photon component), \(D_{\text{n}}\) (neutron component), and \(D_{\text{BNC}}\) (BNC component), the following methods were employed. Pairwise microdosimetric spectra, with and without \({}^{10}\)B, were processed using the approach initially described by [PERSON] et al. [6]. The measurements were conducted using the TEPC in single-event modality, without evaluating the total absorbed dose. The dose probability distribution of the lineal energy, normalized to the unit dose, can be analyzed to derive the three dose components relative to the total. The photon component covers  
Figure 3: (**a**) Dose distributions of lineal energy without boron; (**b**) with a concentration of 100 ppm of \({}^{10}\)B. The relative contributions to the dose due to photons, neutrons, and pure BNC interactions are indicated. The BNC component is derived by subtracting the no \({}^{10}\)B curve from the photon-aligned 100 ppm \({}^{10}\)B curve. More details are provided in the text. the spectrum below approximately 20 keV/\(\upmu\)m. The full distribution was obtained using a pure \(yd(y)\) gamma spectrum aligned with the measured spectra, both with and without \({}^{10}\)B, to reconstruct the \"e-edge region\" (the shoulder in the photon part of the spectrum at about 10 keV/\(\upmu\)m where the dose decreases). The subtraction of the photon component from the full \(yd(y)\) distributions allows for the determination of the component due to neutrons. It should be noted that in the measurement with boron, the neutron component also encompasses the contribution of BNC events. When comparing distributions measured with and without boron, normalization of the \(d(y)\) distribution implies an adjustment of the height of the different components corresponding to their relative contribution to the total. However, the absolute dose contribution from non-thermal components of a mixed radiation field, particularly the gamma component, must remain the same. Taking this into account, the spectrum with boron was scaled by a constant factor to align its photon component with that of the distribution without \({}^{10}\)B. This scaling assumes that the presence of boron did not significantly alter this part of the spectrum, which is a reasonable approximation based on the very low boron content. Following the alignment of the photon component, the distribution without boron was then subtracted from the boron-inclusive distribution. Finally, the obtained dose distributions \(d(y)\) were used to calculate the relative biological effectiveness (RBE) of the radiation field, a crucial parameter in assessing the efficacy of therapeutic treatments.