To determine the absorbed dose in biological samples when irradiated with an epithermal neutron beam of the VVR-SM reactor (INP AS RUz), calculations were made for a phantom object. The flux modification and Kerma reducing values were determined for the incoming neutron beam that goes into the phantom.

The precise evaluation of the absorbed dose in the tumor defines the successful use of neutron capture therapy (NCT). And the absorbed dose depends on the exact determination of the neutron spectra at the target (tumor) location. For GdNCT planning, it is necessary to consider the effect of beam attenuation (self-shielding) with the Gd element itself, which is used to enhance the absorbed dose in the tumor. To determine the effect of Gd (contained in Magnevist) self-shielding were made model calculation for the human brain with size d=7.5 cm and tumor d=4.5 cm, in which three spheres d=1.2 cm located. Calculations showed that in peripheral tumors self-shielding effect begins to affect from the concentration of 1000 ppm, in deeper tumors at low concentrations. At high concentrations of Gd the photon dose begins to increase, which can create the additional therapy effect.

The aim of the study was to develop a method for evaluation of individual sensitivity of human brain glial tumors using live tumor slices with maximum preservation of the structural organization. Fragments of tumors removed during surgery were used for the study. The samples were stored in sterile saline solution with 5% glucose, cooled to 4 ° C. From the obtained fragments of tumors, slices of human brain tumor tissues with thickness of 3 to 5 mm were prepared. Five slices were prepared from each individual tumor sample, one slice was fixed immediately and used for histological analysis of the control, the second slice was used as control and incubated for 24 hours, the remaining three slices were used for gamma-irradiation with absorbed doses of 5, 10 and 15 Gy. After irradiation, the slices were transferred to fresh saline with 5% glucose, cooled to 4°C, and incubated for 24 hours at 4°C, then fixed in 10% formalin, followed by histological analysis of the degree of tumor tissue necrosis. The radiosensitivity of glial tumor tissues was assessed using a specially developed scale. Studies were conducted on various types of glial tumors in 200 patients and the presence of resistant forms of tumors in individual patients was shown. The data obtained suggest that the developed method can be successfully used for individual prediction of the effectiveness of radiation therapy in patients with glial tumors.

For the study of radio-enhancement effect with Ag and Sm in biological matter at kilovoltage X-ray the quantitative estimation was executed by determining a parameter DEF (dose enhancement factor). The necessary for DEF calculations X-ray tube (45 kVp, with the Cu anode) radiation spectrum is modeled depends on its design and technical parameters. The use of filters for X-ray tube spectrum can increase the DEF value. For calculated X-ray spectra DEF values linearly grow at increasing of the fractions of Ag and Sm elements in the soft tissue. This research clarifies the physical reasons that led to the choice of these elements as targets for X-ray radiation, with an energy range where the photoelectric effect is predominant.

The accumulation of gadolinium in human brain gliomas is estimated after a single intravenous administration of Magnevist. The study is conducted using samples excised during standard surgeries on human brain gliomas. Gadolinium is present in all five examined samples at concentrations of 0.0093 to 0.2384 ng mg–1 (ppm) of tumor tissue.

In our study, the high-sensitivity colour indicator of the absorbed dose of radiation of epithermal neutrons with energy 0 to 10 keV for dosimetry of low-energy neutrons was developed. We had been developed an indicator on the basis of the dye solution of arsenazo III and gadopentetic acid, allowing precisely define of absorbed dose in the range 2 to 10 3 Gy. The properties of arsenazo III as metallic indicator, which changes colour after binding of free ions of metals, were used. Colour of the indicator solution before irradiation and after it is stable enough in time at storage in the dark, at artificial illumination or at scattered sunlight. The developed indicator, consisting of a solution of arsenazo III and gadopentetic acid, allows estimating the absorbed dose of epithermal neutron irradiation with good accuracy and reduces the error of measurement related to changing colour of dye under the influence of other factors (light, temperature etc.) Dosimeter is tissue-equivalent and possesses a high-sensitivity neutron radiation due to the content of gadolinium in solution, which has great neutron capture cross-section. The developed dosimeter persists spectrophotometric characteristics after irradiaion within few weeks that allows to use it for measurement of the absorbed dose, both in real time mode and with the delayed measurement within few weeks.

In this study, we evaluate the features of dose enhancement with Gd contrast agent (Magnevist). Due to the increased relaxation time and high atomic number (z=64) Gd can be used in radiation therapy as a radiosensitizer. To perform a quantitative evaluation of the radiosensitization effect is determined a parameter called the dose enhancement factor - DEF. The DEF values were calculated based on the analysis of the mass absorption coefficients for gadolinium and biological tissue. An increase in DEF is observed when the radiation energy is higher than the K-shell ionization energy of Gd atoms. For the presence of 20315 ppm Gd contrast agent in biological tissue the dose enrichment factor is maximum DEF = 4.12 at photon irradiation energy 60 keV. Also, based on calculations for photon irradiation sources considered high degrees of dose enhancement occur for Am-241, Yb-196, and 100 kVp X-ray tube.

The Geant4 code is used for Monte Carlo modeling of the angular distribution of the neutron yield from an 3 H( d , n ) 4 He reaction in a tritium target, and the effect the collimator unit has on the neutron flux. The number of all nuclear reaction channels in a 232 Th + nat U (50/50%) target per 14.1-MeV neutron is also found, along with the optimum size of the target for the maximum yield of secondary neutrons.

To measure the total neutron cross sections, the authors developed a convenient technique using silicon semiconductor detectors with the simple and compact detecting system. The created technique was used to measure A + n total cross sections at the energy E n = 14.1 MeV for several nuclei in different mass region. The neutron generator NG-150 in D + T regime of neutrons generation is used as fast neutrons source. The results of measurements and their comparison with the appropriate literature values are also presented.

To measure the total neutron cross sections, the authors developed a convenient technique using silicon semiconductor detectors with the simple and compact detecting system. The created technique was used to measure A + n total cross sections at the energy En = 14.1 MeV for several nuclei in different mass region. The neutron generator NG-150 in D + T regime of neutrons generation is used as fast neutrons source. The results of measurements and their comparison with the appropriate literature values are also presented.

The aim of our study was to directly determine the accumulation of gadolinium in glial brain tumors after a single intravenous injection of an MRI contrast agent Magnevist. Study was carried out on samples of glial tumours of human brain extracted during standard brain surgery. The samples from five patients with glial tumours and single Magnevist intravenous injection for MRI in different times before surgery were studied. Samples of two patients with glial tumours and without intravenous administration of Magnevist and other gadolinium containing compounds were studied as control. Gadolinium content in tumour tissues was analyzed by method of neutron activation analysis. It was found that in all five investigated samples gadolinium present in concentrations from 0.0093 to 0.2384 ng/mg (ppm) tumour tissue. In control samples, the gadolinium has not been detected. The correlation between the Gd accumulation and the amount of Magnevist injection during MRI was observed. At present time, the clinical importance of detected effect of gadolinium accumulation in brain tumours after intravenous introduction of pharmacological chelate compounds of gadolinium is not clear enough. As free gadolinium is toxic, so the establishment of fact of gadolinium accumulation in brain tumours can appear significant for interpretation of various unexpected clinical effects in the future.

In the present work, based on publications dedicated to nat Gd natural gadolinium isotopes, characteristics of secondary particles are analysed in details for various neutron-induced reactions.Characteristics of the secondary particles produced in these reactions that make significant contribution to absorbed dose are estimated.It is also established that the main contribution to the absorbed dose is made by secondary particles produced in interactions of neutrons and 155 Gd and 157 Gd isotopes.From comparison of gamma-radiation spectra it is defined that the amount of -quanta with energies 0-400 keV (i.e.effective -quanta) produced in the (n,)-reaction by 155 Gd is higher than that by 157 Gd.Compared spectra of other particles (internal conversion electrons, Auger electrons, x-ray radiation) have shown that earlier used average values of their energy must be defined more precisely.When biological objects are irradiated for approximately 30 minutes by epithermal neutrons in the nat Gd NCT (Gadolinium-based neutron-capture therapy), one should take into account energies of secondary particles produced by 152 Gd, 154 Gd, 156 Gd, 158 Gd and 160 Gd isotopes as they have high linear energy transfer (LET).It is demonstrated that when combined, all these secondary particles can make significant contribution to the absorbed dose at neutron-irradiation of biological objects by the nat Gd NCT technique.

In article are presented the devices and characteristics of channel of epithermal neutrons created on nuclear reactor WWR-SM INP AS of RUz for medical and biologic researches. Realized medical and biologic researches on neutroncapture therapy are discussed. Developed for treatment of radio resistant malignant tumors the Gadolinium neutron capture therapy (GdNCT) is based on the nuclear capture and reactions that occur when 155Gd and 157Gd, which are nonradioactive constituents of natural elemental gadolinium, are irradiated by thermal neutrons with low energy 0.025 eV. In this article, results of scientific researches on development GdNCT in Uzbekistan are presented. The beam of epithermal neutrons with characteristics satisfying the all requirements of IAEA was received. Neutron kerma for biological tissues Kbt n=1,35•10–4 Gr/s and for 1 mg natural gadolinium in 1 g of biological tissues KGd n = 3,1•10–7 Gr/s for this beam was calculated. As gadolinium delivery agent the well-known pharmacological preparation Magnevist was chosen. For absorbed dose calculation, the Magnevist pharmacokinetics was studied after intratumoral injection in mice and intramuscular injection in rats. Results of researches of influence epithermal neutrons beam on binding ability of transport proteins of human blood, on tumor cells С-180 at mice and on surgical material of human stomach adenocarcinoma are presented. Planned scientific researches with application of this beam in Uzbekistan are summarized.

Gadolinium neutron capture therapy (GdNCT) is used for treatment of radioresistant malignant tumors. The absorbed dose in GdNCT can be divided into four primary dose components: thermal neutron, fast neutron, photon and natural gadolinium doses. The most significant is the dose created by natural gadolinium. The amount of gadolinium at the irradiated region is changeable and depends on the gadolinium delivery agent and on the structure of the location where the agent is injected. To de- fine the time dependence of the gadolinium concentration ρ(t) in the irradiated region the pharmacokinetics of gadolinium delivery agent (Magnevist) was studied at intratumoral injection in mice and intramuscular injection in rats. A polynomial approximation was applied to the experimental data and the influence of ρ(t) on the relative change of the absorbed dose of gadolinium was studied.