AB009. Evaporation coefficient as a correction factor for boron quantification in histological sections through neutron autoradiography technique

Background: The neutron autoradiography technique using nuclear track detectors (NTDs) is widely applied to study boron microdistribution in tissue samples previously infused with a boron compound. For this purpose, tissue sections are mounted on an NTD, and by irradiating the assembly with thermal neutrons, the ¹⁰B (n,α) ⁷Li reaction takes place and the resulting particles entering the detector cause permanent damage along their paths. This latent damage can be amplified at light microscopy level by a chemical etching, enabling their observation and quantification. Thus, mapping the nuclear tracks allows the assessment of the spatial distribution of ¹⁰B in the biological sample. For this technique, tissue sections are obtained by freeze slicing using a cryostatic microtome. In the transition to room temperature, they undergo an evaporation process that leads to a thickness reduction. Consequently, a natural amplification of the number of tracks in the detector occurs. Since evaporation implies a loss of weight in the sample, the ¹⁰B concentration can be corrected by an evaporation coefficient (CEv) defined as: CEv = m_s/m_h, where m_h corresponds to the “wet” section mass, measured immediately after the tissue is sectioned in the cryostat, and m_s is the “dry” section mass, measured when the evaporation process is finished. This study aimed to establish reproducible CEv reference values for healthy and tumour tissues across multiple tissues and species.

Methods: A protocol previously established at our laboratory to determine CEv was applied to obtain reproducible results of evaporation curves and reference values of CEv for different tissues of interest. Measurements were carried out in normal liver, lung, kidney, and metastatic lung for different species: BDIX rats, nude mice, hamsters, and sheep. Moreover, different types of tissue coming from a hamster’s cheek pouch oral cancer model (tumor, normal pouch tissue, and precancerous tissue) were also analyzed.

Results: Distributions of the CEv values for each tissue were studied and consistent results were obtained, allowing the establishment of reference values. Furthermore, it was observed that rat tissue CEvs correlate with the characteristic water content measured by desiccation in lung, liver, and kidney reported in the literature.

Conclusions: These results will allow the correct quantification of boron in tissue sections through neutron autoradiography technique.

Keywords: Neutron autoradiography; boron neutron capture therapy; cryosectioning; evaporation dynamics