Measurement of an evaporation coefficient in tissue sections as a correction factor for 10B determination.

Boron neutron capture therapy (BNCT) is a cancer treatment option that combines preferential uptake of a boron compound in tumors and irradiation with thermal neutrons. For treatment planning, the boron concentration in different tissues must be considered. Neutron autoradiography using nuclear track detectors (NTD) can be applied to study both the concentration and microdistribution of boron in tissue samples. Histological sections are obtained from frozen tissue by cryosectioning. When the samples reach room temperature, they undergo an evaporation process, which leads to an increase in the boron concentration. To take this effect into account, certain correction factors (evaporation coefficients, CEv) must be applied. With this aim, a protocol was established to register and analyze mass variation of tissue sections, measured with a semimicro scale. Values of ambient temperature, pressure, and humidity were simultaneously recorded. Reproducible results of evaporation curves and CEv values were obtained for different tissue samples, which allowed the systematization of the procedure. This study could contribute to a more precise determination of boron concentration in tissue samples through the neutron autoradiography technique, which is of great relevance to make dosimetric calculations in BNCT.

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

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.

Neutron autoradiography to study the microdistribution of boron in the lung.

In Argentina, a multi-institutional project has been established to assess the feasibility of applying BNCT ex-situ to the treatment of patients with multiple metastases in both lungs. Within this context, this work aims at applying the neutron autoradiography technique to study boron microdistribution in the lung. A comprehensive analysis of the different aspects for the generation of autoradiographic images of both normal and metastatic BDIX rat lungs was achieved. Histology, boron uniformity, optimal tissue thickness and water content in tissue were explored for the two types of samples. A qualitative and a quantitative analysis were performed. No heterogeneities in uptake were observed in normal lung. Conversely, samples with metastasis showed preferential boron uptake in the tumour areas with respect to surrounding tissue. Surrounding tissue would present a slightly higher uptake of boron than the normal lung. Quantitative results of boron concentration values and ratios determined by neutron autoradiography were obtained. In order to contribute to BNCT dosimetry, further analysis increasing the number of samples is warranted.