Bioneutronics: Thermal scattering in organics tissues and its impact on BNCT dosimetry

Fluorinated borono-phenylalanine for optimizing BNCT: Enhancing boron absorption against hydrogen scattering for thermal neutrons

BACKGROUND

Boron-containing compounds, such as 4-borono-phenylalanine (BPA) are used as drugs for cancer treatment in the framework of Boron Neutron Capture Therapy (BNCT). Neutron irradiation of boron-rich compounds delivered to cancer cells triggers nuclear reactions that destroy cancer cells.

PURPOSE

We provide a modeling of the thermal neutron cross section of BPA, a drug used in Boron Neutron Capture Therapy (BNCT), to quantify the competing contributions of boron absorption against hydrogen scattering, for optimizing BNCT by minimizing the latter.

METHODS

We perform the experimental determination of the total neutron scattering cross section of BPA at thermal and epithermal neutron energies using neutron transmission measurements. We isolate the contribution related to the incoherent scattering by hydrogen atoms as a function of the neutron energy by means of the Average Functional Group Approximation, and we calculate the probability for a neutron of being absorbed as a function of the neutron energy both for BPA and for its variants where either one or all four aromatic hydrogen atoms are substituted by 19 F, and both for the samples with natural occurrence or enriched concentration of 10 B.

RESULTS

While referring to the already available literature for in vivo use of fluorinated BPA, we show that fluorine-rich variants of BPA increase the probability of neutrons being captured by the molecule. As the higher absorption efficiency of fluorinated BPA does not depend on whether the molecule is used in vivo or not, our results are promising for the higher efficiency of the boron neutron capture treatment.

CONCLUSIONS

Our results suggest a new advantage using fluorinated compounds for BNCT, in their optimized interaction with neutrons, in addition to their already known capability to be used for monitoring and pharmacokinetics studies using 19 F-Nuclear Magnetic Resonance or in 18 F-Positron Emission Tomography.

Influence of lung physical density on dose calculation in boron neutron capture therapy for malignant pleural mesothelioma

The boron neutron capture therapy treatment planning systems such as SERA and TSUKUBA Plan, which are mainly based on the Monte Carlo method, require the lung physical density and composition of the tissue for the dose calculation. However, the physical density and composition of lungs may change because of diseases such as pneumonia and emphysema. We investigated the effect of the lung physical density on the neutron flux distribution and dose for the lung and tumor.

Thermal neutron cross sections of amino acids from average contributions of functional groups

The experimental thermal neutron cross sections of the 20 proteinogenic amino acids have been measured over the incident-neutron energy range spanning from 1 meV to 10 keV and data have been interpreted using the multi-phonon expansion based on first-principles calculations. The scattering cross section, dominated by the incoherent inelastic contribution from the hydrogen atoms, can be rationalised in terms of the average contributions of different functional groups, thus neglecting their correlation. These results can be used for modelling the total neutron cross sections of complex organic systems like proteins, muscles, or human tissues from a limited number of starting input functions. This simplification is of crucial importance for fine-tuning of transport simulations used in medical applications, including boron neutron capture therapy as well as secondary neutrons-emission induced during proton therapy. Moreover, the parametrized neutron cross sections allow a better treatment of neutron scattering experiments, providing detailed sample self-attenuation corrections for a variety of biological and soft-matter systems.