## 2 Materials and Methods
### BNCT Irradiation  
The cellular samples were irradiated at the TRIGA Mark II research reactor at LENA (Laboratorio di Energia Nucleare Applicata), University of Pavia, Italy. Cells were irradiated in a position of the existing irradiation facility inside the thermal column of the reactor where the thermal neutron flux is about 8 \(\times\) 10\({}^{7}\) cm\({}^{-2}\) s\({}^{-1}\) at 1 kW, with low epithermal and fast neutron components, as well as low gamma dose [38]. MCF-10A cells were exposed in T25 flasks to 5 kW and 20 kW neutrons for 10 min for each reactor power to yield absorbed doses of 0.5 and 2 Gy, respectively, assuming a boron uptake of 30 ppm. Dosimetry for BNCT experiments consists of calculating by Monte Carlo N-Particle (MCNP6) transport code [38] and the dose deposited in cells by the charged secondary particles set in motion by neutron interaction in cells and in the materials. Neutron flux and spectrum in the cell irradiation position are well known and validated. The calculations were made by projecting the fission neutron source on 6 surfaces surrounding the irradiation position using the SSW/SSR MCNP instructions in order to obtain a better efficiency. A first run was implemented to calculate the reaction rate of neutron captures in boron, nitrogen and hydrogen, to characterize the component of neutron-proton scattering, and to assess the photon dose by electron transport. A second run was carried out by defining a uniform source of protons, alpha particles and \({}^{7}\)Li ions which were transported in the best possible detail to estimate dose. The dose was then normalized using the reaction rate previously calculated and the assumed boron concentration. Specifically, the absorbed dose was calculated considering all the radiation components, as shown in Table 1, of the mixed radiation field of BNCT. This was estimated using a validated TRIGA Mark II reactor model written with MNCP6. Of note, computational dosimetry was obtained by transporting all the secondary particles of the mixed radiation field generated by BNCT in the cell layer, without equilibrium assumptions [39]. Verification of Boron Uptake in Cells  
The actual boron intracellular uptake was evaluated by neutron autoradiography [40] using Solid-State Nuclear Track Detectors (SSNTDs, Mi.am Srl, Piacenza, Italy), i.e., allyl diglycol carbonate (C\({}_{12}\)H\({}_{18}\)O\({}_{7}\)), known as CR-39 (Columbia Resin) and commonly used for particle beam fluence and retrospective calculations in radiobiology. Neutron autoradiography allows performing imaging of boron distributions. Imaging was obtained for each experiment in samples treated the same day and undergoing the same procedure as the ones irradiated for radiobiological assays. On the day of irradiation, a cellular pellet (consisting of about 4 \(\times\) 10\({}^{6}\) cells) was deposited on Mylar films and let dry out for at least 48 h. The films on CR-39 were irradiated at the TRIGA reactor at 20 kW for 30 min, in a position of the facility where the thermal neutron flux is 8 \(\times\) 10\({}^{6}\) cm\({}^{-2}\) s\({}^{-1}\) at 1 kW. After irradiation, the CR-39 detectors were subjected to chemical etching in a PEW\({}_{40}\) (KOH + C\({}_{2}\)H\({}_{5}\)OH + H\({}_{2}\)O) basic solution for 10 min at 70 \({}^{\circ}\)C to enlarge the diameter of the latent tracks and make them visible under microscope observation. For these experiments, a Leica stereomicroscope (Leica Microsystems Srl, Milan, Italy), provided with an integrated camera connected to a PC was used. The images were acquired and processed with Image Pro Plus 7.0.8. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Absorbed Dose [10\({}^{-6}\) Gy s\({}^{-1}\) kW\({}^{-1}\)]** & \\ \hline \({}^{10}\)B(n,alpha)\({}^{7}\)Li & \({}^{14}\)N(n,p)14C & H (n,n\({}^{\prime}\)) H & gamma \\ per ug/g of 10B & & & \\ \hline
5.07 \(\pm\) 0.01 & 8.56 \(\pm\) 0.01 & 3.02 \(\pm\) 0.03 & 17.68 \(\pm\) 0.03 \\ \hline \hline \end{tabular}
\end{table}