ИСТИНА

Immuno-PET is an area of ​​positron emission tomography (PET), the newest diagnostic method that allows you to get images at the molecular level. Since the radioisotope in Immuno-PET attaches to monoclonal antibodies (monAT), it is necessary that the biological monAT half-life coincides with the isotope half-life. Antibodies have half-lives ranging from days to weeks. PET-images, as a rule, provides maximum signal-to-background ratios 2-6 days after the introduction of an antibody-based label to the patient. That why it requires the use of radioactive isotopes with a longer half-life compared to the traditional PET-method. Currently, for the Immuno-PET method, iodine-124 (4.18 days half-life) is used as a radioactive label. However, there are problems with visualization accuracy using I-124. Since its decay with a 63% probability is accompanied by the emission of gamma quanta (603 keV), due to the low energy resolution of the detecting equipment, it is impossible to separate the signal from gamma quanta with an energy of 603 keV from the signal of annihilation gamma quanta. Its leads to a distortion of the obtained using radiofrequency images. Zr-89 has ideal characteristics: it decays with T1/2 = 78.41 h through positron emission and electron capture in the intermediate state 89mY, which decays to stable 89Y through gamma radiation (909 keV) with a half-life of 15.7 s. The low average energy of emitted positrons (395.5 keV) leads to high image resolution, and the mismatch of energies between annihilation gamma rays with an energy of 511 keV and gamma rays with an energy of 909 keV does not allow the latter to interfere with the detection of coincident gamma rays. In addition, Zr is safer to handle, cheaper to manufacture, more stable in vivo, and more efficiently accumulated in tumors than I-124. Traditionally, Zr-89 is producing from yttrium by cyclotrons in reactions 89Y(p, n)89Zr and 89Y(d, 2n)89Zr. In both cases, the technology is complicated by the formation in the reactions (p, 2n) and (d, 3n) of the isotope Zr-88 isotope (83.4 days), which decays into the daughter radioactive isotope Y-88 (106 days). The production of radionuclides at electron accelerators is much more economical and technologically simpler than nucleon accelerators. Since medical sources require high specific activity and radiochemical purity from impurity radionuclides, the use of photonuclear reactions with the release of charged particles allows us to solve this problem and to easily separate the resulting radionuclide from the irradiated matrix.

Будут использоваться активационные методы с использованием ускорителей электронов, прикладные ядерно-спектрометрические методы с применением полупроводниковых спектрометров с детекторами из сверхчистого германия. Мишени природного молибдена и ниобия, а также обогащенные по изотопам молибдена, будут облучаться на ускорителях электронов (микротрон НИИЯФ МГУ с максимальной энергией пучка 55 МэВ и линейный ускоритель электронов Линак-200 ОИЯИ г. Дубна в режимах максимальной энергии пучка 20, 30 и 40 МэВ). Облученные мишени будут исследоваться на полупроводниковых спектрометрах Canberra и Ortec с детекторами из сверхчистого германия. Моделирование условий эксперимента будет осуществляться с использованием программных кодов Geant4 и TALYS.

Было проведено облучение сборки фольг естественных Ta, Nb, Mo тормозным пучком с максимальной энергией гамма-квантов 55 МэВ. Были получены экспериментальные выходы 89Zr после облучения природного ниобия и экспериментальный выход 89Zr после облучения природного молибдена. Было получено, что примесь 88Zr в облученных мишенях крайне незначительна. Также следует отметить, что при использовании молибденовых мишеней одновременно с 89Zr можно также получать 99mTc из 99Mo. M. V. Zheltonozhskaya, V. A. Zheltonozhsky, (...), A. P. Chernyaev et al. Production of zirconium-89 by photonuclear reactions // Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms. — 2020. — Vol. 470. — P. 38–41. https://doi.org/10.1016/j.nimb.2020.03.002