Impact of gadolinium concentration and cell oxygen levels on radiobiological characteristics of gadolinium neutron capture therapy technique in brain tumor treatment

Neutron capture therapy (NCT) with various concentrations of gadolinium (157Gd) is one of the treatment modalities for glioblastoma (GBM) tumors. Current study aims to evaluate how variations of 157Gd concentration and cell oxygen levels can affect the relative biological effectiveness (RBE) of gadolinium neutron capture therapy (GdNCT) technique through a hybrid Monte Carlo (MC) simulation approach. At first, Snyder phantom including a spherical tumor was simulated by Geant4 MC code and relevant energy electron spectra to different 157Gd concentrations including 100, 250, 500, and 1000 ppm were calculated following the neutron irradiation of simulated phantom. Scored energy electron spectra were then imported to Monte Carlo damage simulation (MCDS) code to estimate RBE values (both RBESSB and RBEDSB) at different gadolinium concentrations and oxygen levels from 10 to 100%. The results indicate that variations of 157Gd can affect the energy spectrum of released secondary electrons including Auger electrons. Variation of gadolinium concentration from 100 to 1000 ppm in tumor region can change RBESSB and RBEDSB values by about 0.1% and 0.5%, respectively. Besides, maximum variations of 4.3% and 2% were calculated for RBEDSB and RBESSB when cell oxygen level changed from 10 to 100%. From the results, variations of considered gadolinium and oxygen concentrations during GdNCT can influence RBE values. Nevertheless, due to the not remarkable changes in the intensity of Auger electrons, a slight difference in RBE values would be expected at various 157Gd concentrations, although considerable RBE changes were calculated relevant to the oxygen alternations inside tumor tissue.

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.

Current status and development of neutron radiation for biophysical applications in Colombia

In Colombia, medical physics started formally about 3 decades ago. Two master's programs in medical physics initiated activities at two different universities. In particular, the master's program at the Pontificia Universidad Javeriana has been underway since 2012, and taking into account its projections, a team was established in 2015 in collaboration with the Universidad Distrital Francisco José de Caldas to conduct basic research on cancer treatment using neutron capture therapy (NCT). The primary goal of our initiative is to create the infrastructure required to adapt new technologies in our universities in the future. The long-term objective is to use neutron radiation to study not only NCT but also biomolecules, membranes, and materials. This will require the commissioning of an actual nuclear facility. Our group has been exclusively focused on carrying out calculations with GEANT4 because of its characteristics as open-source software, its accessibility, and its ample worldwide use and validation in the particle physics, nuclear physics, and medical physics communities. In this work, we present some results of our preliminary design for the ion accelerator column of a compact neutron generator. Also, we present the characterization of the kinematical and dose distributions of boron neutron capture processes using Geant4.

Feasibility study of using IRT-T research reactor for BNCT applications

This paper presents the results of neutron and gamma calculations aimed at assessing the feasibility of creating an installation for performing research in the field of NСT at the research reactor IRT-T. Considered aspects of choosing a suitable experimental channel as the basis for the installation being created. The calculation results of possible ways of outlet beam parameters improvement consist of inserting of reflector in channel, BSA with filters and collimator are shown.

BNCT research activities at the Granada group and the project NeMeSis: Neutrons for medicine and sciences, towards an accelerator-based facility for new BNCT therapies, medical isotope production and other scientific neutron applications

The Granada group in BNCT research is currently performing studies on: nuclear and radiobiological data for BNCT, new boron compounds and a new design for a neutron source for BNCT and other applications, including the production of medical radioisotopes. All these activities are described in this report.

Exploring neutron capture therapy with 33S and 10B

The ³³S(n,α)³⁰Si reaction was proposed as cooperative neutron capturer to ¹⁰B(n,α)⁷Li in Neutron Capture Therapy (NCT). At that moment, the available ³³S(n,α)³⁰Si cross-section data were scarce and discrepant in key energy ranges for its use in NCT. Since then, three experiments have been carried out at n_TOF facility at CERN and at Institut Laue-Langevin. These new data are used for the calculation of the dose rate on ICRU-4 tissue by using kerma factors, a simplified model of tissue and a 13.45 keV neutron beam, energy of the most important ³³S(n,α)³⁰Si resonance. A significant enhancement of the dose rate due to the presence of ³³S is shown. In spite of the limitations, the cooperative action of ³³S and ¹⁰B is an interesting possibility to be studied for accelerator-based neutron sources with non-moderated neutrons.

A systematic review of clinical applications of polymer gel dosimeters in radiotherapy

Radiotherapy has rapidly improved because of the use of new equipment and techniques. Hence, the appeal for a feasible and accurate three-dimensional (3D) dosimetry system has increased. In this regard, gel dosimetry systems are accurate 3D dosimeters with high resolution. This systematic review evaluates the clinical applications of polymer gel dosimeters in radiotherapy. To find the clinical applications of polymer gel dosimeters in radiotherapy, a full systematic literature search was performed on the basis of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in electronic databases up to January 31, 2017, with use of search-related terms in the titles and abstracts of articles. A total of 765 articles were screened in accordance with our inclusion and exclusion criteria. Eventually, 53 articles were included in the study. The findings show that most clinical applications of polymer gel dosimeters relate to external radiotherapy. Most of the gel dosimeters studied have acceptable dose accuracy as a 3D dosimeter with high resolution. It is difficult to judge which is the best polymer gel dosimeter to use in a clinical setting, because each gel dosimeter has advantages and limitations. For example, methacrylic acid-based gel dosimeters have high dose sensitivity and low toxicity, while their dose response is beam energy dependent; in contrast, N-isopropylacrylamide gel dosimeters have low dose resolution, but their sensitivity is lower and they are relatively toxic.

Gadolinium borate and iron oxide bioconjugates: Nanocomposites of next generation with multifunctional applications

The systematic investigations concerning the bioconjugation of GdBO₃-Fe₃O₄ nanocomposite and their in vitro biocompatibility with cancer cell lines are reported. The nanocomposites were prepared hydrothermally from magnetite (Fe₃O₄), borax or boric acid and a Gd³⁺ salt. Bioconjugation processes were performed with citric acid and fluorescein isothiocyanate-doped silica, followed by the treatment with folic acid. Overall, the procedure involved "bare or PEGylated Fe₃O₄ as the magnetic core" and "vaterite- or triclinic-type of GdBO₃ as the surface borate layer" for comparative evaluation of the results. The successful vectorization of the nanocomposite particles was demonstrated by quantitative and qualitative analytical data. All bioconjugates displayed soft ferromagnetic properties and negative zeta potential values that are appropriate for biological applications. The ¹⁰B and ¹⁵⁷Gd contents were ca. 10¹⁴ atom/μg making them promising agents for BNCT, GdNCT and the combined GdBNCT. The Gd/Fe molar ratios (0.27-0.63) provided the capability for T1- or dual (T1 + T2) magnetic resonance imaging (MRI). In vitro studies were conducted to investigate the efficiency of targeted FA-conjugated versus non-FA conjugated nanoformulations on Mia-Pa-Ca-2, HeLa and A549 cells. Fluorescence microscopy and flow cytometry data unveiled the essential role of the zeta potential competing with folate targeting in the uptake mechanism. The bioconjugated nanoplatforms of GdBO₃-Fe₃O₄ composite, introduced herein, proved to have potential features of next generation agents for magnetically targeted therapy, fluorescence imaging, magnetic resonance imaging/diagnosis and Neutron Capture Therapy.

Boron delivery agents for neutron capture therapy of cancer

Boron neutron capture therapy (BNCT) is a binary radiotherapeutic modality based on the nuclear capture and fission reactions that occur when the stable isotope, boron-10, is irradiated with neutrons to produce high energy alpha particles. This review will focus on tumor-targeting boron delivery agents that are an essential component of this binary system. Two low molecular weight boron-containing drugs currently are being used clinically, boronophenylalanine (BPA) and sodium borocaptate (BSH). Although they are far from being ideal, their therapeutic efficacy has been demonstrated in patients with high grade gliomas, recurrent tumors of the head and neck region, and a much smaller number with cutaneous and extra-cutaneous melanomas. Because of their limitations, great effort has been expended over the past 40 years to develop new boron delivery agents that have more favorable biodistribution and uptake for clinical use. These include boron-containing porphyrins, amino acids, polyamines, nucleosides, peptides, monoclonal antibodies, liposomes, nanoparticles of various types, boron cluster compounds and co-polymers. Currently, however, none of these have reached the stage where there is enough convincing data to warrant clinical biodistribution studies. Therefore, at present the best way to further improve the clinical efficacy of BNCT would be to optimize the dosing paradigms and delivery of BPA and BSH, either alone or in combination, with the hope that future research will identify new and better boron delivery agents for clinical use.

Gd-DTPA Adsorption on Chitosan/Magnetite Nanocomposites

The synthesis of the chitosan/magnetite nanocomposites is presented. Composites were prepared by co-precipitation of iron(II) and iron(III) salts by aqueous ammonia in the 0.1 % chitosan solution. It was shown that magnetite synthesis in the chitosan medium does not affect the magnetite crystal structure. The thermal analysis data showed 4.6 % of mass concentration of chitosan in the hybrid chitosan/magnetite composite. In the concentration range of initial Gd-DTPA solution up to 0.4 mmol/L, addition of chitosan to magnetite increases the adsorption capacity and affinity to Gd-DTPA complex. The Langmuir and Freundlich adsorption models were applied to describe adsorption processes. Nanocomposites were characterized by scanning electron microscopy (SEM), differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and specific surface area determination (ASAP) methods.

Measurement of the (33)S(n,α) cross-section at n_TOF(CERN): Applications to BNCT

AIM

The main purpose of this work is to present a new (n,α) cross-section measurement for a stable isotope of sulfur, (33)S, in order to solve existing discrepancies.

BACKGROUND

(33)S has been studied as a cooperating target for Boron Neutron Capture Therapy (BNCT) because of its large (n,α) cross-section in the epithermal neutron energy range, the most suitable one for BNCT. Although the most important evaluated databases, such as ENDF, do not show any resonances in the cross-section, experimental measurements which provided data from 10 keV to 1 MeV showed that the lowest-lying and strongest resonance of (33)S(n,α) cross-section occurs at 13.5 keV. Nevertheless, the set of resonance parameters that describe such resonance shows important discrepancies (more than a factor of 2) between them.

MATERIALS AND METHODS

A new measurement of the (33)S(n,α)(30)Si reaction cross-section was proposed to the ISOLDE and Neutron Time-of-Flight Experiments Committee of CERN. It was performed at n_TOF(CERN) in 2012 using MicroMegas detectors.

RESULTS

In this work, we will present a brief overview of the experiment as well as preliminary results of the data analysis in the neutron energy range from thermal to 100 keV. These results will be taken into account to calculate the kerma-fluence factors corresponding to (33)S in addition to (10)B and those of a standard four-component ICRU tissue.

CONCLUSIONS

MCNP simulations of the deposited dose, including our experimental data, shows an important kerma rate enhancement at the surface of the tissue, mainly due to the presence of (33)S.

Tissue composition effect on dose distribution in neutron brachytherapy/neutron capture therapy

AIM

The aim of this study is to assess the effect of the compositions of various soft tissues and tissue-equivalent materials on dose distribution in neutron brachytherapy/neutron capture therapy.

BACKGROUND

Neutron brachytherapy and neutron capture therapy are two common radiotherapy modalities.

MATERIALS AND METHODS

Dose distributions were calculated around a low dose rate (252)Cf source located in a spherical phantom with radius of 20.0 cm using the MCNPX code for seven soft tissues and three tissue-equivalent materials. Relative total dose rate, relative neutron dose rate, total dose rate, and neutron dose rate were calculated for each material. These values were determined at various radial distances ranging from 0.3 to 15.0 cm from the source.

RESULTS

Among the soft tissues and tissue-equivalent materials studied, adipose tissue and plexiglass demonstrated the greatest differences for total dose rate compared to 9-component soft tissue. The difference in dose rate with respect to 9-component soft tissue varied with compositions of the materials and the radial distance from the source. Furthermore, the total dose rate in water was different from that in 9-component soft tissue.

CONCLUSION

Taking the same composition for various soft tissues and tissue-equivalent media can lead to error in treatment planning in neutron brachytherapy/neutron capture therapy. Since the International Commission on Radiation Units and Measurements (ICRU) recommends that the total dosimetric uncertainty in dose delivery in radiotherapy should be within ±5%, the compositions of various soft tissues and tissue-equivalent materials should be considered in dose calculation and treatment planning in neutron brachytherapy/neutron capture therapy.

In vivo evaluation of neutron capture therapy effectivity using calcium phosphate-based nanoparticles as Gd-DTPA delivery agent

PURPOSE

A more immediate impact for therapeutic approaches of current clinical research efforts is of major interest, which might be obtained by developing a noninvasive radiation dose-escalation strategy, and neutron capture therapy represents one such novel approach. Furthermore, some recent researches on neutron capture therapy have focused on using gadolinium as an alternative or complementary for currently used boron, taking into account several advantages that gadolinium offers. Therefore, in this study, we carried out feasibility evaluation for both single and multiple injections of gadolinium-based MRI contrast agent incorporated in calcium phosphate nanoparticles as neutron capture therapy agent.

METHODS

In vivo evaluation was performed on colon carcinoma Col-26 tumor-bearing mice irradiated at nuclear reactor facility of Kyoto University Research Reactor Institute with average neutron fluence of 1.8 × 10(12) n/cm(2). Antitumor effectivity was evaluated based on tumor growth suppression assessed until 27 days after neutron irradiation, followed by histopathological analysis on tumor slice.

RESULTS

The experimental results showed that the tumor growth of irradiated mice injected beforehand with Gd-DTPA-incorporating calcium phosphate-based nanoparticles was suppressed up to four times higher compared to the non-treated group, supported by the results of histopathological analysis.

CONCLUSION

The results of antitumor effectivity observed on tumor-bearing mice after neutron irradiation indicated possible effectivity of gadolinium-based neutron capture therapy treatment.

Pretreatment with buthionine sulfoximine enhanced uptake and retention of BSH in brain tumor

To determine the influence of buthionine sulfoximine (BSO) on boron biodistribution after sulfhydryl borane (BSH) administration for boron neutron capture therapy, the effectiveness of the combination of BSO with sulfhydril- (BSH) and non-sulfhydril (B12H12 and BNH3) boron compounds, and the interval between BSO and BSH administration, the retention of boron in tissues have been evaluated using a 9L rat tumor model. Simultaneous administration of BSH and BSO showed significantly higher boron accumulation compared to that without BSO, however there was no difference in tissue boron level between B12H12 and BNH3 administration with BSO or without BSO. The longer interval (6h) between BSH and BSO administration related to the highest boron concentration in the brain and subcutaneous tumors compared to shorter intervals (0.5, 3h). Boron concentration in subcutaneous and brain tumors was maintained for 6 and 12h after the administration of BSH following BSO pretreatment.

(33)S as a cooperative capturer for BNCT

(33)S is a stable isotope of sulfur for which the emission of an α-particle is the dominant exit channel for neutron-induced reactions. In this work the enhancement of both the absorbed and the equivalent biologically weighted dose in a BNCT treatment with 13.5keV neutrons, due to the presence of (33)S, has been tested by means of Monte Carlo simulations. The kerma-fluence factors for the ICRU-4 tissue have been calculated using standard weighting factors. The simulations depend crucially on the scarce (33)S(n,α)(30)Si cross-section data. The presence of a high resonance at 13.5keV was established by previous authors providing discrepant resonance parameters. No experimental data below 10keV are available. All of this has motivated a proposal of experiment at the n_TOF facility at CERN. A setup was designed and tested in 2011. Some results of the successful test will be shown. The experiment is scheduled for the period November to December 2012.

Tumor growth suppression by gadolinium-neutron capture therapy using gadolinium-entrapped liposome as gadolinium delivery agent

Neutron capture therapy (NCT) is a promising non-invasive cancer therapy approach and some recent NCT research has focused on using compounds containing gadolinium as an alternative to currently used boron-10 considering several advantages that gadolinium offers compared to those of boron. In this study, we evaluated gadolinium-entrapped liposome compound as neutron capture therapy agent by in vivo experiment on colon-26 tumor-bearing mice. Gadolinium compound were injected intravenously via tail vein and allowed to accumulate into tumor site. Tumor samples were taken for quantitative analysis by ICP-MS at 2, 12, and 24 h after gadolinium compound injection. Highest gadolinium concentration was observed at about 2 h after gadolinium compound injection with an average of 40.3 μg/g of wet tumor tissue. We performed neutron irradiation at JRR-4 reactor facility of Japan Atomic Energy Research Institute in Tokaimura with average neutron fluence of 2×10¹² n/cm². The experimental results showed that the tumor growth suppression of gadolinium-injected irradiated group was revealed until about four times higher compared to the control group, and no significant weight loss were observed after treatment suggesting low systemic toxicity of this compound. The gadolinium-entrapped liposome will become one of the candidates for Gd delivery system on NCT.