Enhanced Resolution of Neutron Autoradiography with UV-C Sensitization to Study Boron Microdistribution in Animal Models

Abstract

The assessment of boron microdistribution is essential to evaluate the suitability of boron neutron capture therapy (BNCT) in different biological models. In our laboratory, we have reported a methodology to produce cell imprints on polycarbonate through UV-C sensitization. The aim of this work is to extend the technique to tissue samples in order to enhance spatial resolution. As tissue structure largely differs from cultured cells, several aspects must be considered. We studied the influence of the parameters involved in the imprint and nuclear track formation, such as neutron fluence, different NTDs, etching and UV-C exposure times, tissue absorbance, thickness, and staining, among others. Samples from different biological models of interest for BNCT were used, exhibiting homogeneous and heterogeneous histology and boron microdistribution. The optimal conditions will depend on the animal model under study and the resolution requirements. Both the imprint sharpness and the fading effect depend on tissue thickness. While 6 h of UV-C was necessary to yield an imprint in CR-39, only 5 min was enough to observe clear imprints on Lexan. The information related to microdistribution of boron obtained with neutron autoradiography is of great relevance when assessing new boron compounds and administration protocols and also contributes to the study of the radiobiology of BNCT.

Synthesis and Characterization of B4C-Based Multifunctional Nanoparticles for Boron Neutron Capture Therapy Applications

“…In fact, after 30 min of incubation, about 60% of the cells presented internalized 10 B, and after 2 h, 100% of the cells presented tracks either in the nuclear or in the cytoplasmic region when irradiated with a fluence of 10 13 n/cm 2 s. HeLa cells incubated with FeBNPs for 6 h were irradiated with 10 12 neutron fluence to limit the background noise on Lexan. In this case, it was impossible to carry out accurate 10 B quantification due to the significant overlapping of the tracks deriving from the high local 10 B density [43,52,53]. These results evidenced the presence of a relevant uptake of FeBNPs after 6 h of incubation that can lead to the delivery of high-LET secondary particles to the nuclei (Figure 5).…”

“…with FeBNPs for 6 h were irradiated with 10 neutron fluence to limit the background noise on Lexan. In this case, it was impossible to carry out accurate 10 B quantification due to the significant overlapping of the tracks deriving from the high local 10 B density [43,52,53]. These results evidenced the presence of a relevant uptake of FeBNPs after 6 h of incubation that can lead to the delivery of high-LET secondary particles to the nuclei (Figure 5).…”

“…To perform intracellular neutron autoradiography and to carry out 10 B micro-distribution studies, HeLa cells incubated with FeBNPs were grown on solid-state nuclear tracks detectors (SSNTDs) that later underwent irradiation. This technique is based on previous works by Portu et al [41][42][43]. Specifically, the SSNTD (Lexan, made of polycarbonate of 250 µm thickness) was cut into round dishes 30 mm in diameter.…”

“…It is critical to find the right timing for both etching and UV-C irradiation, in order to obtain the best resolution. An excessive UV-C irradiation, in fact, can lead to considerable track fading [43]. If properly performed, the technique allows for the visualization of the particle tracks as round pits of about 1 µm in size, together with an image of the cell's distribution and internal structure.…”