Critical review, with an optimistic outlook, on Boron Neutron Capture Therapy (BNCT)

Development of an affine transformation based treatment control system for accelerator based boron neutron capture therapy

This study developed and validated an adaptive treatment control system based on affine transformation for accelerator-based boron neutron capture therapy. Accelerator-based boron neutron capture therapy is a form of targeted radiotherapy that uses boron-10 to label tumor cells. When these boron-rich cells interact with neutrons, they produce high-linear energy transfer alpha particles and lithium-7 particles, effectively destroying the tumor cells with precision. The newly developed treatment control system integrates real-time stereoscopic x-ray imaging technology, enabling dynamic adjustments to the treatment plan by continuously monitoring changes in tumors and surrounding tissues. To optimize treatment accuracy, the system employs an affine transformation algorithm, ensuring precise dose delivery and accurate patient positioning. Positioning test results demonstrate that the system excels in its core functionality of ensuring patient positioning accuracy, significantly improving treatment adaptability while minimizing damage to healthy tissues. In addition, the study introduces the accelerator-based boron neutron capture therapy device independently designed and constructed by Lanzhou University. This includes a detailed description of the system's architecture, algorithms, and the principles behind its safety interlock functions. Spatial positioning tests of the device confirmed its high overall positioning accuracy, validating the system's reliability and highlighting its potential for broader applications in cancer treatment.

Synthesis and mechanistic investigation of BPA fluorescent probes targeting BPA for potential application in Boron Neutron Capture Therapy (BNCT)

Boronic acid analogs are crucial in modern organic chemistry and drug development, serving as versatile reagents and intermediates with significant therapeutic applications. This area has gained increased interest with the recent development of the drug 4-boron-L-phenylalanine (L-BPA) for boron neutron capture therapy (BNCT). Fluorescent probe technology offers an essential pathway for imaging drugs in vitro and in vivo, providing high sensitivity with great spatial and temporal resolution for both disease diagnosis and drug development. In this paper, we designed and investigated three fluorescent probes-W-1-NN, W-2-NS and W-3-NO-for sensing 4-boron-L-phenylalanine (L-BPA). Among these, only W-1-NN reacts with L-BPA, resulting in a spectral blue-shift change. This probe can "ratiometrically" and specifically detect L-BPA among various metals, with a limit of detection (LOD) of 7.11 μM. Mechanistic studies revealed that the addition of L-BPA disrupts the inherent ESIPT mechanism of W-1-NN in protonic solutions, resulting in the appearance of a new peak at 372 nm. Additionally, theoretical computational studies have also demonstrated that the complexation of W-1-NN with L-BPA triggers a change in the resonance structure, resulting in a larger energy gap and causing a blue shift in the spectrum. Furthermore, W-1-NN has been successfully applied to the detection of L-BPA in human urine. Therefore, the template probe with N/O as the target and the introduction of N atoms can specifically detect L-BPA. This template probe lays the foundation for the detection of L-BPA, and provides great possibilities for the future realization of the template probe to be connected with different fluorophores to make it emit at long wavelengths to reach the target of the near-infrared.

Effect of Neutron Radiation on 10BPA-Loaded Melanoma Spheroids and Melanocytes

Melanoma is an aggressive disease that arises from mutations in the cells that produce the pigment melanin, melanocytes. Melanoma is characterized by a high mortality rate, due to avoidance of applied therapies and metastasis to other organs. The peculiar features of boron neutron capture therapy (BNCT), particularly its cell-level selectivity, make BNCT a promising modality for melanoma treatment. However, appropriate cellular models should be used to study new therapies or improve the efficacy of existing therapies. Spheroids, which have been used for years for in vitro studies of the efficacy of anti-cancer therapies, have many characteristics shared with tumors through which they can increase the accuracy of the cellular response compared to 2D culture in vitro studies and reduce the use of animals for research in the future. To the best of our knowledge, when we started researching the use of spheroids in BNCT in vitro, there was no publication showing such use. Our study aimed to evaluate the efficacy of a 3D cellular model (spheroids) for testing BNCT on melanoma cells. We assessed boronophenylalanine (10BPA) uptake using inductively coupled plasma mass spectrometry in both spheroids and 2D cultures of melanoma and melanocytes. DNA damage, Ki67 protein expression, and spheroid growth were analyzed. The experimental groups included: (1) IR_B (neutron flux + 50 µg 10B/mL), (2) IR (neutron flux alone), (3) C_B (no irradiation, 50 µg 10B/mL), and (4) C (no irradiation and no treatment with boron). The total absorbed doses were estimated to be 2.1-3.1 Gy for IR_B cells and spheroids as well as 8.3-9.4 Gy for IR_B spheroids, while estimated doses for IR cells were 0.5-1.9 Gy. The results indicated that IR_B spheroids might exhibit a reduced diameter. Melanoma cells in the 3D model showed that their DNA damage levels may be higher than those in the 2D model. Moreover, the Ki67 assay revealed differences in the expression of this marker between irradiated melanoma cell lines. In conclusion, preincubation with 10BPA enhances BNCT efficacy, leading to cell growth inhibition and increased DNA fragmentation. Differences in DNA damage between 2D and 3D models may be due to dissimilarities in cell metabolism caused by a changed cell architecture.

Polyethylene glycol complexed with boronophenylalanine as a potential alternative to fructose-boronophenylalanine complexation to increase cellular uptake for BNCT treatment

OBJECTIVE

Boron Neutron Capture Therapy (BNCT) is a novel precision radiotherapy. The key to BNCT application lies in the effective targeting and retention of the boron-10 (10B) carrier. Among the various compounds studied in clinical settings, 4-boronophenylalanine (BPA) become the most prevalent one currently. However, challenges such as inadequate solubility and restricted tumor accumulation have affected the clinical efficacy of treatment with BPA. Therefore, there is an urgent need to prepare formulations with higher tumor uptake efficiency and increased intratumoral accumulation.

METHODS

polyethylene glycol 400 and BPA were added to methanol and stirred until completely dissolved. The solution was then evaporated to remove methanol, yielding a pale-yellow clear liquid of the PEG400-BPA complex. This complex was then used for in vitro and in vivo experiments, and it was evaluated for inhibition effects after BNCT irradiation in GL261 cells.

RESULTS

Compared to the clinically used fructose-BPA, PEG400-BPA increased the boron uptake in tumor cells nearly twice and exhibited a better tumor-to-normal tissue ratio (T/N) in the in vivo studies. Due to the BNCT efficacy with PEG400-BPA through in vitro experiments, the PEG400-BPA group also had showed significant cell-killing effects.

CONCLUSION

We discovered that PEG400 can form a complex with BPA, significantly improving its water solubility. It provides a simple, long-term stable, easily convertible, and injectable formulation method for the delivery of BPA in BNCT treatment. It also offers new insights for BPA solubilization and formulation as well as compound forms of administration of boron drugs on the delivery of boron drugs in BNCT.

A Bis-Boron Amino Acid for Positron Emission Tomography and Boron Neutron Capture Therapy

Trifluoroborate boronophenylalanine (BBPA) is a boron amino acid analog of 4-boronophenylalanine (BPA) but with a trifluoroborate group (-BF3 -) instead of a carboxyl group (-COOH). Clinical studies have shown that 18F-labeled BBPA ([18F]BBPA) can produce high-contrast tumor images in positron emission tomography (PET). Beyond PET imaging, BBPA is a theranostic agent for boron neutron capture therapy (BNCT). Because BBPA possesses an identical chemical structure to BNCT and PET, it can potentially predict the boron concentration for BNCT using [18F]BBPA-PET. The synthesis of BBPA was achieved by selectively fluorinating the α-aminoborate compound, taking advantage of the varying rates of solvolysis of the B-F bond. The study showcased the high-contrast [18F]BBPA-PET imaging in various tumor models, highlighting its broad applicability for both [18F]BBPA-PET and BBPA-BNCT. [18F]BBPA-PET tumor uptake remains consistent across various doses, including those used in BNCT. This enables accurate estimation of the boron concentration in tumors using [18F]BBPA-PET. With its dual boron structure, BBPA increases boron concentration in tumor cells and tumor tissues compared to BPA. Thus, less boron carrier is needed. This study introduces a new theranostic boron carrier that enhances boron accumulation in tumors, predicts boron concentration, and enhances the accuracy and effectiveness of BNCT.

A Comparative Study of Neutron Shielding Performance in Al-Based Composites Reinforced with Various Boron-Containing Particles for Radiotherapy: A Monte Carlo Simulation

This study aimed to assess and compare the shielding performance of boron-containing materials for neutrons generated in proton therapy and used in boron neutron capture therapy (BNCT). Five composites, including AlB2, Al-B4C, Al-TiB2, Al-BN, and Al-TiB2-BN, were selected as shielding materials, with concrete used as a benchmark. The mass fraction of boron compounds in these materials ranged from 10% to 50%. The Monte Carlo toolkit Geant4 was employed to calculate shielding parameters, including neutron ambient dose equivalent, dose values, and macroscopic cross-section. Results indicated that, compared to concrete, these boron-containing materials more effectively absorb thermal neutrons. When the boron compound exceeds 30 wt.%, these materials exhibit better shielding performance than concrete of the same thickness for neutrons generated by protons. For a given material, its shielding capability increases with boron content. Among the five materials when the material thickness and boron compound content are the same, the shielding performance for neutrons generated by protons, from best to worst, is as follows: Al-TiB2, Al-B4C, AlB2, Al-TiB2-BN, and Al-BN. For BNCT, the shielding performance from best to worst is in the following order: Al-B4C, AlB2, Al-TiB2, Al-TiB2-BN, and Al-BN. The results of this study provide references and guidelines for the selection and optimization of neutron shielding materials in proton therapy and BNCT facilities.

Recent advances in spatio-temporally controllable systems for management of glioma

Malignant glioma remains one of the most aggressive intracranial tumors with devastating clinical outcomes despite the great advances in conventional treatment approaches, including surgery and chemotherapy. Spatio-temporally controllable approaches to glioma are now being actively investigated due to the preponderance, including spatio-temporal adjustability, minimally invasive, repetitive properties, etc. External stimuli can be readily controlled by adjusting the site and density of stimuli to exert the cytotoxic on glioma tissue and avoid undesired injury to normal tissues. It is worth noting that the removability of external stimuli allows for on-demand treatment, which effectively reduces the occurrence of side effects. In this review, we highlight recent advancements in drug delivery systems for spatio-temporally controllable treatments of glioma, focusing on the mechanisms and design principles of sensitizers utilized in these controllable therapies. Moreover, the potential challenges regarding spatio-temporally controllable therapy for glioma are also described, aiming to provide insights into future advancements in this field and their potential clinical applications.

Incorporating boron distribution variations in microdosimetric kinetic model-based relative biological effectiveness calculations for boron neutron capture therapy

This study introduces the MKM_B model, an approach derived from the MKM model, designed to evaluate the biological effectiveness of Boron Neutron Capture Therapy (BNCT) in the face of challenges from varying microscopic boron distributions. The model introduces a boron compensation factor, allowing for the assessment of compound Biological Effectiveness (CBE) values for different boron distributions. Utilizing the TOPAS simulation platform, the lineal energy spectrum of particles in BNCT was simulated, and the sensitivity of the MKM_B model to parameter variations and the influence of cell size on the model were thoroughly investigated. The CBE values for 10B-boronphenylalanine (BPA) and 10B-sodium (BSH) were determined to be 3.70 and 1.75, respectively. These calculations were based on using the nucleus radius of 2.5 μm and the cell radius of 5 μm while considering a 50% surviving fraction. It was observed that as cell size decreased, the CBE values for both BPA and BSH increased. Additionally, the model parameter rd was identified as having the most significant impact on CBE, with other parameters showing moderate effects. The development of the MKM_B model enables the accurate prediction of CBE under different boron distributions in BNCT. This model offers a promising approach to optimize treatment planning by providing increased accuracy in biological effectiveness.

Towards New Delivery Agents for Boron Neutron Capture Therapy: Synthesis and In Vitro Evaluation of a Set of Fluorinated Carbohydrate Derivatives

Boron Neutron Capture Therapy (BNCT) is a cancer treatment which combines tumor-selective boron delivery agents with thermal neutrons in order to selectively eradicate cancer cells. In this work, we focus on the early-stage development of carbohydrate delivery agents for BNCT. In more detail, we expand upon our previous GLUT-targeting approach by synthesizing and evaluating the potential embedded in a representative set of fluorinated carbohydrates bearing a boron cluster. Our findings indicate that these species may have advantages over the boron delivery agents in current clinical use, e.g., significantly improved boron delivery capacity at the cellular level. Simultaneously, the carbohydrate delivery agents were found to bind strongly to plasma proteins, which may be a concern requiring further action before progression to in vivo studies. Altogether, this work brings new insights into factors which need to be accounted for if attempting to develop theranostic agents for BNCT based on carbohydrates in the future.

Boron Neutron Capture Therapy Enhanced by Boronate Ester Polymer Micelles: Synthesis, Stability, and Tumor Inhibition Studies

Boron neutron capture therapy (BNCT) targets invasive, radioresistant cancers but requires a selective and high B-10 loading boron drug. This manuscript investigates boron-rich poly(ethylene glycol)-block-(poly(4-vinylphenyl boronate ester)) polymer micelles synthesized via atom transfer radical polymerization for their potential application in BNCT. Transmission electron microscopy (TEM) revealed spherical micelles with a uniform size of 43 ± 10 nm, ideal for drug delivery. Additionally, probe sonication proved effective in maintaining the micelles' size and morphology postlyophilization and reconstitution. In vitro studies with B16-F10 melanoma cells demonstrated a 38-fold increase in boron accumulation compared to the borophenylalanine drug for BNCT. In vivo studies in a B16-F10 tumor-bearing mouse model confirmed enhanced tumor selectivity and accumulation, with a tumor-to-blood (T/B) ratio of 2.5, surpassing BPA's T/B ratio of 1.8. As a result, mice treated with these micelles experienced a significant delay in tumor growth, highlighting their potential for BNCT and warranting further research.

Carborane-FAPI conjugate: A potential FAP-targeted boron agent with improved boron content

Boron neutron capture therapy (BNCT) has received extensive attention as an advanced binary radiotherapy method. However, BNCT still faces poor selectivity of boron agent and is insufficient boron content in tumor tissues. To improve the tumor-targeted ability and boron content, this research aims to design, synthesize and preliminary evaluate a new borane agent Carborane-FAPI, which coupling the o-carborane to the compound skeleton of a mature fibroblast activating protein (FAP) inhibitor (FAPI). FAP is a tumor-associated antigen. FAP expressed lowly in normal organs and highly expressed in tumors, so it is a potential target for diagnosis and treatment. Boronophenylalanine (BPA) is the most widely investigated BNCT drug in present. Compared with BPA, the boron content of a single molecule is increased and drug targeting is enhanced. The results show that Carboaren-FAPI has low toxicity to normal cells, and selective enrichment in tumor tissues. It is a promising boron drug that has the potential to be used in BNCT.

Active control of pharmacokinetics using light-responsive polymer-drug conjugates for boron neutron capture therapy

In boron neutron capture therapy (BNCT), boron drugs should exhibit high intratumoral boron concentrations during neutron irradiation, while being cleared from the blood and normal organs. However, it is usually challenging to achieve such tumor accumulation and quick clearance simultaneously in a temporally controlled manner. Here, we developed a polymer-drug conjugate that can actively control the clearance of the drugs from the blood. This polymer-drug conjugate is based on a biocompatible polymer that passively accumulates in tumors. Its side chains were conjugated with the low-molecular-weight boron drugs, which are immediately excreted by the kidneys, via photolabile linkers. In a murine subcutaneous tumor model, the polymer-drug conjugate could accumulate in the tumor with the high boron concentration ratio of the tumor to the surrounding normal tissue (∼10) after intravenous injection while a considerable amount remained in the bloodstream as well. Photoirradiation to blood vessels through the skin surface cleaved the linker to release the boron drug in the blood, allowing for its rapid clearance from the bloodstream. Meanwhile, the boron concentration in the tumor which was not photoirradiated could be maintained high, permitting strong BNCT effects. In clinical BNCT, the dose of thermal neutrons to solid tumors is determined by the maximum radiation exposure to normal organs. Thus, our polymer-drug conjugate may enable us to increase the therapeutic radiation dose to tumors in such a practical situation.

Fluorinated BPA derivatives enhanced 10B delivery in tumors

Boron neutron capture therapy (BNCT) is an emerging approach for treating malignant tumors with binary targeting. However, its clinical application has been hampered by insufficient 10B accumulation in tumors and low 10B concentration ratios of tumor-to-blood (T/B) and tumor-to-normal tissue (T/N). Herein, we developed fluorinated BPA derivatives with different fluorine groups as boron delivery agents for enabling sufficient 10B accumulation in tumors and enhancing T/B and T/N ratios. Our findings demonstrated that fluorinated BPA derivatives had good biological safety. Furthermore, fluorinated BPA derivatives showed improved 10B accumulation in tumors and enhanced T/B and T/N ratios compared to the clinical boron drug fructose-BPA (f-BPA). In particular, in B16-F10 tumor-bearing mice, fluorinated BPA derivatives met the requirements for clinical BNCT even at half of the clinical dose. Thus, fluorinated BPA derivatives are potentially effective boron delivery agents for clinical BNCT in melanoma.

Synthesis of Gd-DTPA Carborane-Containing Compound and Its Immobilization on Iron Oxide Nanoparticles for Potential Application in Neutron Capture Therapy

Cancer is one of the leading causes of global mortality, and its incidence is increasing annually. Neutron capture therapy (NCT) is a unique anticancer modality capable of selectively eliminating tumor cells within normal tissues. The development of accelerator-based, clinically mountable neutron sources has stimulated a worldwide search for new, more effective compounds for NCT. We synthesized magnetic iron oxide nanoparticles (NPs) that concurrently incorporate boron and gadolinium, potentially enhancing the effectiveness of NCT. These magnetic nanoparticles underwent sequential modifications through silane polycondensation and allylamine graft polymerization, enabling the creation of functional amino groups on their surface. Characterization was performed using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive X-ray (EDX), dynamic light scattering (DLS), thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM). ICP-AES measurements indicated that boron (B) content in the NPs reached 3.56 ppm/mg, while gadolinium (Gd) averaged 0.26 ppm/mg. Gadolinium desorption was observed within 4 h, with a peak rate of 61.74%. The biocompatibility of the NPs was confirmed through their relatively low cytotoxicity and sufficient cellular tolerability. Using NPs at non-toxic concentrations, we obtained B accumulation of up to 5.724 × 1010 atoms per cell, sufficient for successful NCT. Although limited by its content in the NP composition, the Gd amount may also contribute to NCT along with its diagnostic properties. Further development of the NPs is ongoing, focusing on increasing the boron and gadolinium content and creating active tumor targeting.

Fluorine-18 labeling PEGylated 6-boronotryptophan for PET scanning of mice for assessing the pharmacokinetics for boron neutron capture therapy of brain tumors

Two tryptophan compound classes 5- and 6-borono PEGylated boronotryptophan derivatives have been prepared for assessing their aqueous solubility as formulation of injections for boron neutron capture therapy (BNCT). The PEGylation has improved their aqueous solubility thereby increasing their test concentration in 1 mM without suffering from toxicity. In-vitro uptake assay of PEGylated 5- and 6-boronotryptophan showed that the B-10 concentration can reach 15-50 ppm in U87 cell whereas the uptake in LN229 cell varies. Shorter PEG compound 6-boronotryptophanPEG200[18F] was obtained in 1.7 % radiochemical yield and the PET-derived radioradioactivity percentage in 18 % was taken up by U87 tumor at the limb of xenograft mouse. As high as tumor to normal uptake ratio in 170 (T/N) was obtained while an inferior radioactivity uptake of 3 % and T/N of 8 was observed in LN229 xenografted mouse.

Highly Efficient and Eco-Friendly Thermal-Neutron-Shielding Materials Based on Recycled High-Density Polyethylene and Gadolinium Oxide Composites

Due to the increasing demands for improved radiation safety and the growing concerns regarding the excessive use of plastics, this work aimed to develop effective and eco-friendly thermal-neutron-shielding materials based on recycled high-density polyethylene (r-HDPE) composites containing varying surface-treated gadolinium oxide (Gd2O3) contents (0, 5, 10, 15, and 20 wt%). The results indicate that the overall thermal-neutron-shielding properties of the r-HDPE composites were enhanced with the addition of Gd2O3, as evidenced by large reductions in I/I0, HVL, and TVL, as well as the substantial increases in ∑t and ∑t/ρ of the composites. Furthermore, the results reveal that the values for tensile properties initially increased up to 5-15 wt% of Gd2O3 and then gradually decreased at higher contents. In addition, the results show that the addition of Gd2O3 particles generally increased the density (ρ), the remaining ash at 600 °C, and the degree of crystallinity (%XC) of the composites. This work also determined the effects of gamma irradiation on relevant properties of the composites. The findings indicate that following gamma aging, the tensile modulus slightly increased, while the tensile strength, elongation at break, and hardness (Shore D) showed no significant (p < 0.05) differences, except for the sample containing 5 wt% of Gd2O3, which exhibited a noticeable reduction in elongation at break. Furthermore, by comparing the neutron-shielding and mechanical properties of the developed r-HDPE composites with common borated polyethylene (PE) containing 5 wt% and 15 wt% of boron, the results clearly indicate the superior shielding and tensile properties in the r-HDPE composites, implying the great potential of r-HDPE composites to replace virgin plastics as effective and more eco-friendly shielding materials.

Targeting the organelle for radiosensitization in cancer radiotherapy

Radiotherapy is a well-established cytotoxic therapy for local solid cancers, utilizing high-energy ionizing radiation to destroy cancer cells. However, this method has several limitations, including low radiation energy deposition, severe damage to surrounding normal cells, and high tumor resistance to radiation. Among various radiotherapy methods, boron neutron capture therapy (BNCT) has emerged as a principal approach to improve the therapeutic ratio of malignancies and reduce lethality to surrounding normal tissue, but it remains deficient in terms of insufficient boron accumulation as well as short retention time, which limits the curative effect. Recently, a series of radiosensitizers that can selectively accumulate in specific organelles of cancer cells have been developed to precisely target radiotherapy, thereby reducing side effects of normal tissue damage, overcoming radioresistance, and improving radiosensitivity. In this review, we mainly focus on the field of nanomedicine-based cancer radiotherapy and discuss the organelle-targeted radiosensitizers, specifically including nucleus, mitochondria, endoplasmic reticulum and lysosomes. Furthermore, the organelle-targeted boron carriers used in BNCT are particularly presented. Through demonstrating recent developments in organelle-targeted radiosensitization, we hope to provide insight into the design of organelle-targeted radiosensitizers for clinical cancer treatment.

Targeted strategies to deliver boron agents across the blood-brain barrier for neutron capture therapy of brain tumors

Boron neutron capture therapy (BNCT), as an innovative radiotherapy technology, has demonstrated remarkable outcomes when compared to conventional treatments in the management of recurrent and refractory brain tumors. However, in BNCT of brain tumors, the blood-brain barrier is a main stumbling block for restricting the transport of boron drugs to brain tumors, while the tumor targeting and retention of boron drugs also affect the BNCT effect. This review focuses on the recent development of strategies for delivering boron drugs crossing the blood-brain barrier and targeting brain tumors, providing new insights for the development of efficient boron drugs for the treatment of brain tumors.

A dose calculation algorithm for boron neutron capture therapy using convolution/superposition method

The convolution/superposition (C/S) method originally designed for photon dose calculation was first applied for developing a treatment planning system for boron neutron capture therapy. The original concept of TEGMA (total energy generated per unit mass) was proposed to represent distinctive dose components from neutron reactions with the elements in the patient's tissue. First, neutron fluence distributions in a homogeneous brain phantom irradiated with an energy-groupwise pencil beam of 2.5 × 2.5 mm2 were calculated using the MCNP6.2 code. Then, a library of energy-groupwise TEGMA and KERMA were generated and stored in the developed C/S code. As a benchmark, dose distributions in a cuboid phantom and a human head phantom were calculated using the developed C/S and PHITS Monte Carlo codes. A neutron beam having a continuous epithermal spectrum and a square field of 22.5 × 22.5 mm2 or a circle field of 22.5 mm in diameter was assumed to be incident on the phantoms. The human head phantom was created by the pre-processing including the voxelization and transformation of test DICOM CT images. The differences in boron doses between C/S and MC ranged from 2% to 6%. In nitrogen doses, the differences were from 4% to 9%. A large discrepancy observed in hydrogen lateral dose profiles could be explained by the differences in cross-section data and recoil-proton transport algorithms of MCNP6.2 and PHITS. With isodose curves normalized at the center of the tumor in the human head phantom, they were almost identical in the range of 60%-110% for both cases. The C/S have underestimated the backscattering neutron and showed a larger absorbed dose gradient around 40% region. The calculation time of C/S using Intel i7-10700 processor was less than 1 min for both phantoms. The calculation time of PHITS using three Intel Xeon E5-2640 v4 processors was 15.5 min for the cuboid phantom and ∼380 min for the human head phantom. The proposed algorithm has the advantages of high speed while promising fair accuracy in BNCT dose calculations.

Development of a Gadolinium-Boron-Conjugated Albumin for MRI-Guided Neutron Capture Therapy

Noninvasive monitoring of boron agent biodistribution is required in advance of neutron capture therapy. In this study, we developed a gadolinium-boron-conjugated albumin (Gd-MID-BSA) for MRI-guided neutron capture therapy. Gd-MID-BSA was prepared by labeling bovine serum albumin with a maleimide-functionalized gadolinium complex and a maleimide-functionalized closo-dodecaborate orthogonally. The accumulation of Gd-MID-BSA in tumors in CT26 tumor-bearing mice reached a maximum at 24 h after the injection, as confirmed by T1-based MRI and biodistribution analysis using inductively coupled plasma optical emission spectrometry. The concentrations of boron and gadolinium in the tumors exceeded the thresholds required for boron neutron capture therapy (BNCT) and gadolinium neutron capture therapy (GdNCT), respectively. The boron concentration ratios of tumor to blood and tumor to normal tissues satisfied the clinical criteria, indicating the reduction of undesired nuclear reactions of endogenous nuclei. The molar ratio of boron to gadolinium in the tumor was close to that of Gd-MID-BSA, demonstrating that the accumulation of Gd-MID-BSA in the tumor can be evaluated by MRI. Thermal neutron irradiation with Gd-MID-BSA resulted in significant suppression of tumor growth compared to the group injected with a boron-conjugated albumin without gadolinium (MID-BSA). The neutron irradiation with Gd-MID-BSA did not cause apparent side effects. These results demonstrate that the conjugation of gadolinium and boron within the albumin molecule offers a novel strategy for enhancing the therapeutic effect of BNCT and the potential of MRI-guided neutron capture therapy as a promising treatment for malignant tumors.

In vivo investigation of boron-rich nanodrugs for treating triple-negative breast cancers via boron neutron capture therapy

Triple-negative breast cancer (TNBC) is characterized by highly proliferative cancer cells and is the only subtype of breast cancer that lacks a targeted therapy. Boron neutron capture therapy (BNCT) is an approach that combines chemotherapy with radiotherapy and can potentially offer beneficial targeted treatment for TNBC patients owing to its unique ability to eradicate cancer cells selectively while minimizing damage to the surrounding healthy cells. Since BNCT relies on specific delivery of a high loading of B10 to the tumor site, there is growing research interest to develop more potent boron-based drugs for BNCT that can overcome the limitations of small-molecule boron compounds. In this study, polyethylene-glycol-coated boron carbon oxynitride nanoparticles (PEG@BCNO) of size 134.2±23.6nm were prepared as a promising drug for BNCT owing to their high boron content and enhanced biocompatibility. The therapeutic efficiency of PEG@BCNO was compared with a state-of-the-art 10BPA boron drug in mice bearing MDA-MB-231 tumor. In the orthotopic mouse model, PEG@BCNO showed higher B10 accumulation in the tumor tissues (6 μg 10B/g tissue compared to 3 μg 10B/g tissue in mice administered B10-enriched 10BPA drug) despite using the naturally occurring 11B/10B boron precursor in the preparation of the BCNO nanoparticles. The in vivo biodistribution of PEG@BCNO in mice bearing MDA-MB-231 showed a tumor/blood ratio of ~3.5, which is comparable to that of the state-of-the-art 10BPA-fructose drug. We further demonstrated that upon neutron irradiation, the mice bearing MDA-MB-231 tumor cells treated with PEG@BCNO and 10BPA showed tumor growth delay times of 9 days and 1 day, respectively, compared to mice in the control group after BNCT. The doubling times (DTs) for mice treated with PEG@BCNO and 10BPA as well as mice in the control group were calculated to be 31.5, 19.8, and 17.7 days, respectively. Immunohistochemical staining for the p53 and caspase-3 antibodies revealed that mice treated with PEG@BCNO showed lower probability of cancer recurrence and greater level of cellular apoptosis than mice treated with 10BPA and mice in the control group. Our study thus demonstrates the potential of pegylated BCNO nanoparticles in effectively inhibiting the growth of TNBC tumors compared to the state-of-the-art boron drug 10BPA.

Proposal of recommended experimental protocols for in vitro and in vivo evaluation methods of boron agents for neutron capture therapy

Recently, boron neutron capture therapy (BNCT) has been attracting attention as a minimally invasive cancer treatment. In 2020, the accelerator-based BNCT with L-BPA (Borofalan) as its D-sorbitol complex (Steboronine®) for head and neck cancers was approved by Pharmaceutical and Medical Devices Agency for the first time in the world. As accelerator-based neutron generation techniques are being developed in various countries, the development of novel tumor-selective boron agents is becoming increasingly important and desired. The Japanese Society of Neutron Capture Therapy believes it is necessary to propose standard evaluation protocols at each stage in the development of boron agents for BNCT. This review summarizes recommended experimental protocols for in vitro and in vivo evaluation methods of boron agents for BNCT based on our experience with L-BPA approval.

A transdermal drug delivery system based on dissolving microneedles for boron neutron capture therapy of melanoma

Boron neutron capture therapy (BNCT) is a promising therapy for malignant tumors that requires selective and high concentrations of 10B accumulation in tumor cells. Despite ongoing developments in novel boron agents and delivery carriers, the progress and clinical application of BNCT is still restricted by the low 10B accumulation and tumor-to-normal tissue (T/N) ratio. Herein, a dissolving microneedle-based transdermal drug delivery system was specifically designed for BNCT in a mouse model of melanoma. By incorporating fructose-BPA (F-BPA) into PVA microneedle tips, this system successfully delivered sufficient F-BPA into the melanoma site after the application of only two patches. Notably, the T/N ratio achieved through the treatment combining PVA/F-BPA MNs with BNCT (PVA/F-BPA MNs-BNCT) surpassed 93.16, signifying a great improvement. Furthermore, this treatment approach effectively inhibited tumor growth and significantly enhanced the survival rate of the mice. In brief, our study introduces a novel, simple, and efficient administration strategy for BNCT, opening new possibilities for the design of nanomedicine for BNCT.

Boron in cancer therapeutics: An overview

Boron has become a crucial weapon in anticancer research due to its significant intervention in cell proliferation. Being an excellent bio-isosteric replacement of carbon, it has modulated the anticancer efficacy of various molecules in the development pipeline. It has elicited promising results through interactions with various therapeutic targets such as HIF-1α, steroid sulfatase, arginase, proteasome, etc. Since boron liberates alpha particles, it has a wide-scale application in Boron Neutron Capture therapy (BNCT), a radiotherapy that demonstrates selectivity towards cancer cells due to high boron uptake capacity. Significant advances in the medicinal chemistry of boronated compounds, such as boronated sugars, natural/unnatural amino acids, boronated DNA binders, etc., have been reported over the past few years as BNCT agents. In addition, boronated nanoparticles have assisted the field of bio-nano medicines by their usage in radiotherapy. This review exclusively focuses on the medicinal chemistry aspects, radiotherapeutic, and chemotherapeutic aspects of boron in cancer therapeutics. Emphasis is also given on the mechanism of action along with advantages over conventional therapies.

Synthesis and Characterization of Boron Carbide Nanoparticles as Potential Boron-Rich Therapeutic Carriers

Boron carbide is one of the hardest materials in the world which can be synthesized by various methods. The most common one is a carbothermic or magnesiothermic reduction of B2O3 performed at high temperatures, where the obtained powder still requires grinding and purification. The goal of this research is to present the possibility of synthesizing B4C nanoparticles from elements via vapor deposition and modifying the morphology of the obtained powders, particularly those synthesized at high temperatures. B4C nanoparticles were synthesized in the process of direct synthesis from boron and carbon powders heated at the temperature of 1650 °C for 2 h under argon and characterized by using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction analysis, and dynamic light scattering measurements. The physicochemical characteristics of B4C nanoparticles were determined, including the diffusion coefficients, hydrodynamic diameter, electrophoretic mobilities, and zeta potentials. An evaluation of the obtained B4C nanoparticles was performed on several human and mouse cell lines, showing the relation between the cytotoxicity effect and the size of the synthesized nanoparticles. Assessing the suitability of the synthesized B4C for further modifications in terms of its applicability in boron neutron capture therapy was the overarching goal of this research.

Nanostructured boron agents for boron neutron capture therapy: a review of recent patents

Boron neutron capture therapy (BNCT) is a potential radiation therapy modality for cancer, and tumor-targeted stable boron-10 (10B) delivery agents are an important component of BNCT. Currently, two low-molecular-weight boron-containing compounds, sodium mercaptoundecahydro-closo-dodecaborate (BSH) and boronophenylalanine (BPA), are mainly used in BNCT. Although both have suboptimal tumor selectivity, they have shown some therapeutic benefit in patients with high-grade glioma and several other tumors. To improve the efficacy of BNCT, great efforts have been devoted for the development of new boron delivery agents with better uptake and favorable pharmacokinetic profiles. This article reviews the application and research progress of boron nanomaterials as boron carriers in boron neutron capture therapy and hopes to stimulate people's interest in nanomaterial-based delivery agents by summarizing various kinds of boron nanomaterial patents disclosed in the past decade.

Study of Nuclear Reactions in Therapy of Tumors with Proton Beams

This paper presents an assessment of nuclear reaction yields of protons, α-particles, and neutrons in human tissue-equivalentmaterial in proton therapy using a simulation with Geant 4. In this study, we also check an enhancement of nuclear reactions due to the presence of Bi, Au, 11B, and 10B radiosensitizer nanoparticles. We demonstrate that a proton beam induces a noticeable amount of nuclear reactions in the tissue. Nevertheless, the enhancement of nuclear reaction products due to radiosensitizer nanoparticles is found to be negligible.

Microdosimetric Analysis for Boron Neutron Capture Therapy via Monte Carlo Track Structure Simulation with Modified Lithium Cross-sections

Boron neutron capture therapy (BNCT) is a cellular-level hadron therapy achieving therapeutic effects via the synergistic action of multiple particles, including Lithium, alpha, proton, and photon. However, evaluating the relative biological effectiveness (RBE) in BNCT remains challenging. In this research, we performed a microdosimetric calculation for BNCT using the Monte Carlo track structure (MCTS) simulation toolkit, TOPAS-nBio. This paper reports the first attempt to derive the ionization cross-sections of low-energy (>0.025 MeV/u) Lithium for MCTS simulation based on the effective charge cross-section scalation method and phenomenological double-parameter modification. The fitting parameters λ 1 = 1.101 , λ 2 = 3.486 were determined to reproduce the range and stopping power data from the ICRU report 73. Besides, the lineal energy spectra of charged particles in BNCT were calculated, and the influence of sensitive volume (SV) size was discussed. Condensed history simulation obtained similar results with MCTS when using Micron-SV while overestimating the lineal energy when using Nano-SV. Furthermore, we found that the microscopic boron distribution can significantly affect the lineal energy for Lithium, while the effect for alpha is minimal. Similar results to the published data by PHITS simulation were observed for the compound particles and monoenergetic protons when using micron-SV. Spectra with nano-SV reflected that the different track densities and absorbed doses in the nucleus together result in the dramatic difference in the macroscopic biological response of BPA and BSH. This work and the developed methodology could impact the research fields in BNCT where understanding radiation effects is crucial, such as the treatment planning system, source evaluation, and new boron drug development.

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.

Perceptions of Canadian Radiation Oncologists, Medical Physicists, and Radiation Trainees about the Feasibility and Need of Boron Neutron Capture Therapy (BNCT) in Canada: A National Survey

BACKGROUND

Boron Neutron Capture Therapy (BNCT) is an emerging radiotherapy. There are ongoing efforts to develop a Canadian accelerator-based BNCT center. However, it remains unclear how Canadian radiation oncologists (RO), medical physicists (MP), and their trainees perceive BNCT and its impact on radiation oncology as a discipline.

METHODS

A survey was created to explore the knowledge of BNCT, its clinical role, and the support for Canadian research. It was distributed through the Canadian Association of Radiation Oncology (CARO) and the Canadian Organization of Medical Physicists (COMP).

RESULTS

We received 118 valid responses from all 10 provinces, from 70 RO (59.3%) and 48 MP (40.7%), including 9 residents. Most knew of BNCT and its indications (60.2%). Although many were unaware of the reasons behind early failures (44.1%), common reasons were a lack of clinical trials and an inaccessibility of neutron sources (42.4%) as well as reactor unsuitability (34.7%). Additionally, 90.6% showed definite (66.9%) or possible (23.7%) support for Canadian BNCT research, while 89% indicated a definite (56.8%) or possible (32.2%) willingness for BNCT referrals.

CONCLUSIONS

Most ROs and MPs supported Canadian BNCT research and would refer patients. However, limited awareness and a lack of experiences remain a challenge. Educational sessions are needed to realize this innovative cancer treatment in Canada.

Multi-Functional Boron-Delivery Agents for Boron Neutron Capture Therapy of Cancers

Boron neutron capture therapy (BNCT) is a binary cancer treatment that involves the irradiation of ¹⁰B-containing tumors with low-energy neutrons (thermal or epithermal). The alpha particles and recoiling Li nuclei that are produced in the ¹⁰B-capture nuclear reaction are high-linear-energy transfer particles that destroy boron-loaded tumor cells; therefore, BNCT has the potential to be a localized therapeutic modality. Two boron-delivery agents have been used in clinical trials of BNCT in patients with malignant brain tumors, cutaneous melanoma, or recurrent tumors of the head and neck region, demonstrating the potential of BNCT in the treatment of difficult cancers. A variety of potentially highly effective boron-delivery agents have been synthesized in the past four decades and tested in cells and animal models. These include boron-containing nucleosides, peptides, proteins, polyamines, porphyrins, liposomes, monoclonal antibodies, and nanoparticles of various types. The most promising agents are multi-functional boronated molecules and nanoparticles functionalized with tumor cell-targeting moieties that increase their tumor selectivity and contain a radiolabel or fluorophore to allow quantification of ¹⁰B-biodistribution and treatment planning. This review discusses multi-functional boron agents reported in the last decade, but their full potential can only be ascertained after their evaluation in BNCT clinical trials.

Robust Thermal Neutron Detection by LiInP2 Se6 Bulk Single Crystals

Direct neutron detection based on semiconductor crystals holds promise to transform current neutron detector technologies and further boosts their widespread applications. It is, however, long impeded by the dearth of suitable materials in the form of sizeable bulk crystals. Here, high-quality centimeter-sized LiInP₂ Se₆ single crystals are developed using the Bridgman method and their structure and property characteristics are systematically investigated. The prototype detectors fabricated from the crystals demonstrate an energy resolution of 53.7% in response to α-particles generated from an ²⁴¹ Am source and robust, well-defined response spectra to thermal neutrons that exhibit no polarization or degradation effects under prolonged neutron/γ-ray irradiation. The primary mechanisms of Se-vacancy and In_Li antisite defects in the carrier trapping process are also identified. Such insights are critical for further enhancing the energy resolution of LiInP₂ Se₆ bulk crystals toward the intrinsic level (≈8.6% as indicated by the chemical vapor transport-grown thin crystals). These results pave the way for practically adopting LiInP₂ Se₆ single crystals in new-generation solid-state neutron detectors.

Enhancement in the Therapeutic Efficacy of In Vivo BNCT Mediated by GB-10 with Electroporation in a Model of Oral Cancer

Boron neutron capture therapy (BNCT) combines preferential tumor uptake of ¹⁰B compounds and neutron irradiation. Electroporation induces an increase in the permeability of the cell membrane. We previously demonstrated the optimization of boron biodistribution and microdistribution employing electroporation (EP) and decahydrodecaborate (GB-10) as the boron carrier in a hamster cheek pouch oral cancer model. The aim of the present study was to evaluate if EP could improve tumor control without enhancing the radiotoxicity of BNCT in vivo mediated by GB-10 with EP 10 min after GB-10 administration. Following cancerization, tumor-bearing hamster cheek pouches were treated with GB-10/BNCT or GB-10/BNCT + EP. Irradiations were carried out at the RA-3 Reactor. The tumor response and degree of mucositis in precancerous tissue surrounding tumors were evaluated for one month post-BNCT. The overall tumor response (partial remission (PR) + complete remission (CR)) increased significantly for protocol GB-10/BNCT + EP (92%) vs. GB-10/BNCT (48%). A statistically significant increase in the CR was observed for protocol GB-10/BNCT + EP (46%) vs. GB-10/BNCT (6%). For both protocols, the radiotoxicity (mucositis) was reversible and slight/moderate. Based on these results, we concluded that electroporation improved the therapeutic efficacy of GB-10/BNCT in vivo in the hamster cheek pouch oral cancer model without increasing the radiotoxicity.

Localized nuclear reaction breaks boron drug capsules loaded with immune adjuvants for cancer immunotherapy

Boron neutron capture therapy (BNCT) was clinically approved in 2020 and exhibits remarkable tumour rejection in preclinical and clinical studies. It is binary radiotherapy that may selectively deposit two deadly high-energy particles (4He and 7Li) within a cancer cell. As a radiotherapy induced by localized nuclear reaction, few studies have reported its abscopal anti-tumour effect, which has limited its further clinical applications. Here, we engineer a neutron-activated boron capsule that synergizes BNCT and controlled immune adjuvants release to provoke a potent anti-tumour immune response. This study demonstrates that boron neutron capture nuclear reaction forms considerable defects in boron capsule that augments the drug release. The following single-cell sequencing unveils the fact and mechanism that BNCT heats anti-tumour immunity. In female mice tumour models, BNCT and the controlled drug release triggered by localized nuclear reaction causes nearly complete regression of both primary and distant tumour grafts.

Synthesis and Structures of Lead(II) Complexes with Hydroxy-Substituted Closo-Decaborate Anions

Mixed-ligand lead(II) complexes with 2,2′-bipyridyl and [B10H9OH]2− or monosubstituted hydroxy-substituted closo-decaborate anions with a pendant hydroxy group, separated from the boron cage by an alkoxylic spacer of different lengths [B10H9O(CH2)xO(CH2)2OH]]2− (x = 2 or 5) have been synthesized. Compounds have been characterized by IR and multinuclear NMR spectroscopies. The structures of binuclear complex [Pb(bipy)2[B10H9OH]]2·CH3CN (1·CH3CN), mononuclear complex [Pb(bipy)2[B10H9O(CH2)2O(CH2)2OH]]·0.5bipy·CH3CN (2·0.5bipy·CH3CN), and polymeric complex [Pb(bipy)[B10H9O(CH2)5O(CH2)2OH]]n (3) have been determined by single-crystal X-ray diffraction. In all three compounds, the co-ordination polyhedra of lead(II) are formed by N atoms from two bipy molecules, O atoms of the substituent attached to the boron cage, and BH groups of the boron cage.

Development of a 2-(2-Hydroxyphenyl)-1H-benzimidazole-Based Fluorescence Sensor Targeting Boronic Acids for Versatile Application in Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is an attractive approach to treating cancers. Currently, only one ¹⁰B-labeled boronoagent (Borofalan, BPA) has been approved for clinical BNCT in Japan, and methods for predicting and measuring BNCT efficacy must be established to support the development of next-generation ¹⁰B-boronoagents. Fluorescence sensors targeting boronic acids can achieve this because the amount and localization of ¹⁰B in tumor tissues directly determine BNCT efficacy; however, current sensors are nonoptimal given their slow reaction rate and weak fluorescence (quantum yield < 0.1). Herein, we designed and synthesized a novel small molecular-weight fluorescence sensor, BITQ, targeting boronic acids. In vitro qualitative and quantitative properties of BITQ were assessed using a fluorophotometer and a fluorescence microscope together with BPA quantification in blood samples. BITQ exhibited significant quantitative and selective fluorescence after reacting with BPA (post-to-pre-fluorescence ratio = 5.6; quantum yield = 0.53); the fluorescence plateaued within 1 min after BPA mixing, enabling the visualization of intracellular BPA distribution. Furthermore, BITQ quantified the BPA concentration in mouse blood with reliability comparable with that of current methods. This study identifies BITQ as a versatile fluorescence sensor for analyzing boronic acid agents. BITQ will contribute to ¹⁰B-boronoagent development and promote research in BNCT.

Carborane bearing pullulan nanogel-boron oxide nanoparticle hybrid for boron neutron capture therapy

Boron neutron capture therapy shows is a promising approach to cancer therapy, but the delivery of effective boron agents is challenging. To address the requirements for efficient boron delivery, we used a hybrid nanoparticle comprising a carborane = bearing pullulan nanogel and hydrophobized boron oxide nanoparticle (HBNGs) enabling the preparation of highly concentrated boron agents for efficient delivery. The HBNGs showed better anti-cancer effects on Colon26 cells than a clinically boron agent, L-BPA/fructose complex, by enhancing the accumulation and retention amount of the boron agent within cells in vitro. The accumulation of HBNGs in tumors, due to the enhanced permeation and retention effect, enabled the delivery of boron agents with high tumor selectivity, meeting clinical demands. Intravenous injection of boron neutron capture therapy (BNCT) using HBNGs decreased tumor volume without significant body weight loss, and no regrowth of tumor was observed three months after complete regression. The therapeutic efficacy of HBNGs was better than that of L-BPA/fructose complex. BNCT with HBNGs is a promising approach to cancer therapeutics.

Construction of targeted 10B delivery agents and their uptake in gastric and pancreatic cancer cells

Boron Neutron Capture Therapy (BNCT) is a new binary radiation therapy for tumor tissue, which kills tumor cells with neutron capture reaction. Boron neutron capture therapy has become a technical means for glioma, melanoma, and other diseases has been included in the clinical backup program. However, BNCT is faced with the key problem of developing and innovating more efficient boron delivery agents to solve the targeting and selectivity. We constructed a tyrosine kinase inhibitor-L-p-boronophenylalanine (TKI-BPA) molecule, aiming to improve the selectivity of boron delivery agents by conjugating targeted drugs while increasing the molecular solubility by adding hydrophilic groups. It shows excellent selectivity in differential uptake of cells, and its solubility is more than 6 times higher than BPA, leading to the saving of boron delivery agents. This modification method is effective for improving the efficiency of the boron delivery agent and is expected to become a potential alternative with high clinical application value.

Use of a neural network-based prediction method to calculate the therapeutic dose in boron neutron capture therapy of patients with glioblastoma

BACKGROUND

Boron neutron capture therapy (BNCT) is a binary radiotherapy based on the ¹⁰ B(n, α)⁷ Li capture reaction. Nonradioactive isotope ¹⁰ B atoms which selectively concentrated in tumor cells will react with low energy neutrons (mainly thermal neutrons) to produce secondary particles with high linear energy transfer, thus depositing dose in tumor cells. In clinical practice, an appropriate treatment plan needs to be set on the basis of the treatment planning system (TPS). Existing BNCT TPSs usually use the Monte Carlo method to determine the three-dimensional (3D) therapeutic dose distribution, which often requires a lot of calculation time due to the complexity of simulating neutron transportation.

PURPOSE

A neural network-based BNCT dose prediction method is proposed to achieve the rapid and accurate acquisition of BNCT 3D therapeutic dose distribution for patients with glioblastoma to solve the time-consuming problem of BNCT dose calculation in clinic.

METHODS

The clinical data of 122 patients with glioblastoma are collected. Eighteen patients are used as a test set, and the rest are used as a training set. The 3D-UNET is constructed through the design optimization of input and output data sets based on radiation field information and patient CT information to enable the prediction of 3D dose distribution of BNCT.

RESULTS

The average mean absolute error of the predicted and simulated equivalent doses of each organ are all less than 1 Gy. For the dose to 95% of the GTV volume (D₉₅ ), the relative deviation between predicted and simulated results are all less than 2%. The average 2 mm/2% gamma index is 89.67%, and the average 3 mm/3% gamma index is 96.78%. The calculation takes about 6 h to simulate the 3D therapeutic dose distribution of a patient with glioblastoma by Monte Carlo method using Intel Xeon E5-2699 v4, whereas the time required by the method proposed in this study is almost less than 1 s using a Titan-V graphics card.

CONCLUSIONS

This study proposes a 3D dose prediction method based on 3D-UNET architecture in BNCT, and the feasibility of this method is demonstrated. Results indicate that the method can remarkably reduce the time required for calculation and ensure the accuracy of the predicted 3D therapeutic dose-effect. This work is expected to promote the clinical development of BNCT in the future.

Recent Development of Radiofluorination of Boron Agents for Boron Neutron Capture Therapy of Tumor: Creation of 18F-Labeled C-F and B-F Linkages

Boron neutron capture therapy (BNCT) is a binary therapeutic technique employing a boron agent to be delivered to the tumor site followed by the irradiation of neutrons. Biofunctional molecules/nanoparticles labeled with F-18 can provide an initial pharmacokinetic profile of patients to guide the subsequent treatment planning procedure of BNCT. Borono phenylalanine (BPA), recognized by the l-type amino acid transporter, can cross the blood-brain barrier and be accumulated in gliomas. The radiofluoro BNCT agents are reviewed by considering (1) less cytotoxicity, (2) diagnosing and therapeutic purposes, (3) aqueous solubility and extraction route, as well as (4), the trifluoroborate effect. A trifluoroborate-containing amino acid such as fluoroboronotyrosine (FBY) represents an example with both functionalities of imaging and therapeutics. Comparing with the insignificant cytotoxicity of clinical BPA with IC50 > 500 μM, FBY also shows minute toxicity with IC50 > 500 μM. [18F]FBY is a potential diagnostic agent for its tumor to normal accumulation (T/N) ratio, which ranges from 2.3 to 24.5 from positron emission tomography, whereas the T/N ratio of FBPA is greater than 2.5. Additionally, in serving as a BNCT therapeutic agent, the boron concentration of FBY accumulated in gliomas remains uncertain. The solubility of 3-BPA is better than that of BPA, as evidenced by the cerebral dose of 3.4%ID/g vs. 2.2%ID/g, respectively. While the extraction route of d-BPA differs from that of BPA, an impressive T/N ratio of 6.9 vs. 1.5 is noted. [18F]FBPA, the most common clinical boron agent, facilitates the application of BPA in clinical BNCT. In addition to [18F]FBY, [18F] trifluoroborated nucleoside analog obtained through 1,3-dipolar cycloaddition shows marked tumoral uptake of 1.5%ID/g. Other examples using electrophilic and nucleophilic fluorination on the boron compounds are also reviewed, including diboronopinacolone phenylalanine and nonsteroidal anti-inflammatory agents.

7Be and 22Na radionuclides for a new therapy for cancer

10B isotopes have been almost exclusively used in the neutron-capture radiation therapy (NCT) of cancer for decades. We have identified two other nuclides suitable for radiotherapy, which have ca. ten times larger cross section of absorption for neutrons and emit heavy charged particles. This would provide several key advantages for potential NCT, such as the possibility to use a lower nuclide concentration in the target tissues or a lower neutron irradiation flux. By detecting the characteristic γ radiation from the spontaneous decay of the radionuclides, one can image their biodistribution. These advantages could open up new possibilities for NCT applications as a safer and more efficient cancer therapy.

SARU: A self-attention ResUNet to generate synthetic CT images for MR-only BNCT treatment planning

PURPOSE

Despite the significant physical differences between magnetic resonance imaging (MRI) and computed tomography (CT), the high entropy of MRI data indicates the existence of a surjective transformation from MRI to CT image. However, there is no specific optimization of the network itself in previous MRI/CT translation works, resulting in mistakes in details such as the skull margin and cavity edge. These errors might have moderate effect on conventional radiotherapy, but for boron neutron capture therapy (BNCT), the skin dose will be a critical part of the dose composition. Thus, the purpose of this work is to create a self-attention network that could directly transfer MRI to synthetical computerized tomography (sCT) images with lower inaccuracy at the skin edge and examine the viability of magnetic resonance (MR)-guided BNCT.

METHODS

A retrospective analysis was undertaken on 104 patients with brain malignancies who had both CT and MRI as part of their radiation treatment plan. The CT images were deformably registered to the MRI. In the U-shaped generation network, we introduced spatial and channel attention modules, as well as a versatile "Attentional ResBlock," which reduce the parameters while maintaining high performance. We employed five-fold cross-validation to test all patients, compared the proposed network to those used in earlier studies, and used Monte Carlo software to simulate the BNCT process for dosimetric evaluation in test set.

RESULTS

Compared with UNet, Pix2Pix, and ResNet, the mean absolute error (MAE) of self-attention ResUNet (SARU) is reduced by 12.91, 17.48, and 9.50 HU, respectively. The "two one-sided tests" show no significant difference in dose-volume histogram (DVH) results. And for all tested cases, the average 2%/2 mm gamma index of UNet, ResNet, Pix2Pix, and SARU were 0.96 ± 0.03, 0.96 ± 0.03, 0.95 ± 0.03, and 0.98 ± 0.01, respectively. The error of skin dose from SARU is much less than the results from other methods.

CONCLUSIONS

We have developed a residual U-shape network with an attention mechanism to generate sCT images from MRI for BNCT treatment planning with lower MAE in six organs. There is no significant difference between the dose distribution calculated by sCT and real CT. This solution may greatly simplify the BNCT treatment planning process, lower the BNCT treatment dose, and minimize image feature mismatch.

Boron Vehiculating Nanosystems for Neutron Capture Therapy in Cancer Treatment

Boron neutron capture therapy is a low-invasive cancer therapy based on the neutron fission process that occurs upon thermal neutron irradiation of ¹⁰B-containing compounds; this process causes the release of alpha particles that selectively damage cancer cells. Although several clinical studies involving mercaptoundecahydro-closo-dodecaborate and the boronophenylalanine-fructose complex are currently ongoing, the success of this promising anticancer therapy is hampered by the lack of appropriate drug delivery systems to selectively carry therapeutic concentrations of boron atoms to cancer tissues, allowing prolonged boron retention therein and avoiding the damage of healthy tissues. To achieve these goals, numerous research groups have explored the possibility to formulate nanoparticulate systems for boron delivery. In this review. we report the newest developments on boron vehiculating drug delivery systems based on nanoparticles, distinguished on the basis of the type of carrier used, with a specific focus on the formulation aspects.

Exploring the Physical and Biological Aspects of BNCT with a Carboranylmethylbenzo[b]acridone Compound in U87 Glioblastoma Cells

Boron neutron capture therapy (BNCT) is a re-emerging technique for selectively killing tumor cells. Briefly, the mechanism can be described as follows: after the uptake of boron into cells, the thermal neutrons trigger the fission of the boron atoms, releasing the α-particles and recoiling lithium particles and high-energy photons that damage the cells. We performed a detailed study of the reactor dosimetry, cellular dose assessment, and radiobiological effects induced by BNCT in glioblastoma (GBM) cells. At maximum reactor power, neutron fluence rates were ϕ0 = 6.6 × 107 cm−2 s−1 (thermal) and θ = 2.4 × 104 cm−2 s−1 with a photon dose rate of 150 mGy·h−1. These values agreed with simulations to within 85% (thermal neutrons), 78% (epithermal neutrons), and 95% (photons), thereby validating the MCNPX model. The GEANT4 simulations, based on a realistic cell model and measured boron concentrations, showed that >95% of the dose in cells was due to the BNC reaction. Carboranylmethylbenzo[b]acridone (CMBA) is among the different proposed boron delivery agents that has shown promising properties due to its lower toxicity and important cellular uptake in U87 glioblastoma cells. In particular, the results obtained for CBMA reinforce radiobiological effects demonstrating that damage is mostly induced by the incorporated boron with negligible contribution from the culture medium and adjacent cells, evidencing extranuclear cell radiosensitivity.

A Design for the High Yield Photoneutron Source Target Station

Low energy accelerator driven neutron sources are promising candidates to obtain a neutron yield as high as 10¹⁴ n/s, which is required for a variety of applications, such as boron neutron capture therapy, neutron imaging, and neutron scattering. The methods to generate neutrons can be divided into two categories: hadron-based and photon-based methods. In order to better understand which kind of source would be the better choice for delivering a brilliant neutron beam robustly, in this paper, the underlying principles of neutron production, as well as the simulation results of neutron yield, target heat dissipation, thermal stress, and reaction byproducts concentration of these two types of neutron sources, will be elaborated on. A preliminary photoneutron target station design based on a 50 MeV/50 kW electron linear accelerator, including the optimized neutron yield, thermal hydraulic analysis, and shielding calculation, is presented as well to demonstrate the method to deliver brilliant thermal neutron beam of 1.03 × 10¹⁰ cm^-2 s^-1 sr^-1.

A Red-Emitting Fluorescence Sensor for Detecting Boronic Acid-Containing Agents in Cells

The amount and localization of boron-10 atoms delivered into tumor cells determines the therapeutic effect of boron neutron capture therapy (BNCT) and, consequently, efforts have been directed to develop fluorescence sensors to detect intracellular boronic acid compounds. Currently, these sensors are blue-emitting and hence are impracticable for co-staining with nucleus staining reagents, such as DAPI and Hoechst 33342. Here, we designed and synthesized a novel fluorescence boron sensor, BS-631, that emits fluorescence with a maximum emission wavelength of 631 nm after reaction with the clinically available boronic acid agent, 4-borono-l-phenylalanine (BPA). BS-631 quantitatively detected BPA with sufficiently high sensitivity (detection limit = 19.6 µM) for evaluating BNCT agents. Furthermore, BS-631 did not emit fluorescence after incubation with metal cations. Notably, red-emitting BS-631 could easily and clearly visualize the localization of BPA within cells with nuclei co-stained using Hoechst 33342. This study highlights the promising properties of BS-631 as a versatile boron sensor for evaluating and analyzing boronic acid agents in cancer therapy.