Radiation Technologies in Medicine: The Role of Secondary Particles in Forming Doses
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ation Technologies in Medicine: The Role of Secondary Particles in Forming Doses P. P. Gantsovskya, M. V. Zheltonozhskayab, A. Yu. Komarova, E. N. Lykovac, *, A. G. Tsovyanova, A. P. Chernyaevb, c, F. Yu. Smirnova, Yu. P. Zinchenkob, M. S. Kovyazinab, and R. S. Shilkob aState
Research Center Burnasyan Federal Medical Biophysical Center, Federal Medical Biological Agency, Moscow, 123098 Russia b Moscow State University, Moscow, 119991 Russia cSkobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received June 18, 2020; revised July 10, 2020; accepted July 27, 2020
Abstract—The Bonner sphere technique with activation foil made of natural tantalum is used to estimate doses during secondary particle irradiation. The neutron spectrum in the isocenter of a Varian Trilogy medical linear accelerator (linac) is calculated. The average neutron energy and the effective neutron cross section are determined. The flux of the (γ, n) reaction is calculated using a measured spectrum. The fluxes measured using Bonner spheres with a natural tantalum activation target correspond to the results from similar measurements obtained in other ways. DOI: 10.3103/S1062873820110106
INTRODUCTION Modern nuclear physics has become an integral part of medical technologies. Medicine now has more than 110 000 high-tech devices for diagnostic and therapeutic purposes that use sources of ionizing radiation (e.g., X-ray tubes, natural and artificial isotopes, and accelerators). Around 13 000 accelerators have now been used in radiation therapy, including 136 heavycharged-particle accelerators, >400 tomotherapy
facilities, 200 intraoperative radiation therapy units, and ~350 cyber knives (Table 1) [1]. In this work, we consider the physical principles of improving and developing nuclear technologies in medicine. An important line of such research is the role of fluxes of secondary neutrons. It was assumed for many years that these fluxes were negligible during the operation of medical accelerators, and their contribution to an integral dose could be ignored.
Table 1. High-tech medical devices in Russia and the world in 2020 Device Accelerators 60Со
sources of gamma radiation
World
Russia
~13000
~220
~2000
~236
Gamma cameras and SPECT
~17000
~281
Computer tomographs
~40000
~1100
MRT
~30000
~ 500
~4000
54
PET centers
~600
18
Gamma knife
~300
5
Cyber knife
~300
9
~2200
~150
PET scanners
Brachytherapy facilities Proton and ion therapy complexes X-ray units 1330
136
5
~4 mln
55000
RADIATION TECHNOLOGIES IN MEDICINE
Beams of bremsstrahlung photons that form on the bremsstrahlung targets of linacs with electron energies of 6 to 20 MeV are used most often in radiation therapy. At energies higher than 8 MeV (where many photonuclear reaction channels open), bremsstrahlung photons produce fluxes of secondary neutrons as they interact with the accelerator’s elements and materials of the medical unit’s construction [2, 3]. Since the source of a medical accelerator’s
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