ИСТИНА

Usage of charged particle accelerators for radiotherapy in such techniques as the methods of proton and ion beam therapy is one of the promising areas in the treatment of cancer. A characteristic feature of the beams of protons and light ions is the presence of the Bragg peak in a function of the specific energy loss at different depths in the substance. This allows to localize the process of energy release during radiotherapy irradiation with high accuracy. Compared to radiation therapy using low-energy gamma-ray beams, interaction of charged particles with energies of up to several hundred MeV with the matter involves significantly more complicated processes leading to the generation of secondary particles (in particular, neutrons) and rescattering effects. A notable source of such secondary neutrons is constituted by photonuclear reactions triggered by bremsstrahlung photons. An inherent part of radiotherapy treatment is computer simulation, which is used for irradiation planning and dosimetry monitoring. Currently, simulation packages based on the Monte Carlo method are widely used for detailed calculation of the transport of particles of ionizing radiation in particle beam therapy. The present work considers nuclear reactions leading to the emission of secondary neutrons on stable W isotopes. Tungsten is a frequently used material in accelerator technology. In particular, multileaf collimators (MLC), made of it, are used in nuclear medicine to form a beam in close proximity to the patient, and in the process of irradiation this can become a source of increased neutron background for him. In this work, using the method of induced activity at the facility [1], experimental yields of reactions with the neutron emission occuring in a tungsten target under the action of an electron beam with an energy of 55 MeV were obtained. These results are compared with the calculations of the generation of secondary neutrons, performed using the Monte-Carlo GEANT4 package [2], as well as with the yields of the corresponding photonuclear reactions, calculated on the basis of the available tabular and theoretical cross sections. The obtained data provide a measure of the accuracy of neutron dose calculation in GEANT4 when used for prediction of irradiation exposure in radiation therapy. [1] K. A. Stopani et al. // Nucl. Instrum. Meth. in Phys. Res. A. 2014. V. 745. P. 133. [2] S. Agostinelli et al. // Nucl. Instrum. Meth. in Phys. Res. A. 2003. V. 506. P. 250.