CN-122025364-A - Fast scanning magnet for homogenizing proton beam current of boron neutron capture treatment system based on high-current cyclotron

CN122025364ACN 122025364 ACN122025364 ACN 122025364ACN-122025364-A

Abstract

The invention belongs to the technical field of nuclear medicine and electromagnetic intersection, and particularly relates to a rapid scanning magnet for homogenizing proton beam of a boron neutron capture treatment system based on a strong current cyclotron, which comprises a magnetic yoke and an exciting coil, wherein the magnetic yoke is made of ferrite, the height of an air gap is determined by matching according to the outer diameter of a beam vacuum tube, the proton beam vacuum tube is a large-caliber beam channel which is determined by taking the inner diameter of the proton beam vacuum tube as targets for scanning and targeting, beam corona expansion and collimation errors of the proton beam, the exciting coil comprises two groups which are respectively arranged on two opposite magnetic pole surfaces in a magnetic window and are positioned at two sides of the air gap, and the ratio of the width of the magnetic pole surface of the magnetic yoke and the height of the air gap and the size and the space layout of the exciting coil meet that the uniformity deviation of an integral field in a good field is less than 1 percent. The invention can solve the problems of temperature rise, slow magnetic field response and uniformity degradation of an integral field caused by eddy current effect of the scanning magnet in the existing BNCT system under the condition of rapid excitation.

Inventors

CHEN QUSHAN
LIU YIPING
QIN BIN
LIU XU
JIN LIANGZAN

Assignees

华中科技大学

Dates

Publication Date: 20260512
Application Date: 20260331

Claims (7)

1. A fast scan magnet for homogenizing proton beam of a boron neutron capture treatment system based on a high-current cyclotron, which is arranged at the upstream of a neutron conversion target of the treatment system along the beam transmission direction in a pairwise orthogonal mode to form a two-dimensional scan unit, wherein the scan magnet for x-direction scanning continuously scans at a frequency of 200 Hz and above, and is characterized by comprising a magnet yoke and an exciting coil; The magnetic yoke is made of ferrite, an opening area surrounded by the magnetic yoke is of a rectangular window structure, the height of an air gap is determined by matching according to the outer diameter of a proton beam vacuum tube to be penetrated, and mechanical allowance is reserved while the requirement of the proton beam vacuum tube with a large caliber is met, wherein the proton beam vacuum tube is a large caliber beam channel which is determined by taking the inner diameter of the proton beam vacuum tube as targets for scanning and targeting, beam halo expansion and collimation errors, the exciting coil comprises two groups which are respectively arranged on two opposite magnetic pole faces in the rectangular window structure and are positioned on two sides of the air gap, and the proportion of the width of the magnetic pole face of the magnetic yoke and the height of the air gap and the size and the space layout of the exciting coil are determined by taking the uniformity deviation of an integral field in a preset field area in the proton beam vacuum tube as targets of less than 1%.
2. A fast scan magnet according to claim 1, wherein the portion of each set of field coils extending beyond the air gap is bent away from the air gap and attached to the yoke such that the field coils are saddle-shaped.
3. The rapid-scan magnet of claim 1, wherein the exciting coil is hollow, a cooling water channel is arranged in the conductor to form a water-cooled coil structure, and the cooling condition satisfies the water flow speed of less than 3m/s, the Reynolds number Re of more than 2300 and the loop pressure drop of not more than 10bar.
4. A fast scan magnet according to claim 3, wherein each set of exciting coils has 15 turns, the coil conductors are hollow copper conductors with outer square and inner round, the cross section of the conductors is 11 x 11mm2, and water cooling holes with diameter phi of 5mm are arranged in the conductors.
5. A proton beam fast scan system for a high current cyclotron-based boron neutron capture therapy system, comprising a proton beam transport vacuum tube, a first split scan magnet SMX, a second split scan magnet SMY disposed orthogonal to the SMX, a detector, and a neutron conversion target, wherein the SMX and the SMY are both scan magnets as set forth in any one of claims 1 to 4.
6. The proton beam fast scan system according to claim 5, wherein the exciting current of the SMX is a triangular wave reciprocating scan waveform for implementing reciprocating linear scan in the x-direction, and the exciting current of the SMY is a step wave reciprocating scan waveform for implementing progressive scan in the y-direction.
7. The proton beam fast scan system according to claim 5, wherein the number of steps of the step wave is determined according to a density distribution in a y direction of a cluster drifting from a system entrance to a target center, and the beam intensity distribution in a target range is flat-topped and uniformity is higher than a preset value by setting a step wave level and a step width.

Description

Fast scanning magnet for homogenizing proton beam current of boron neutron capture treatment system based on high-current cyclotron Technical Field The invention belongs to the technical field of nuclear medicine and electromagnetic intersection, and particularly relates to a fast scanning magnet for homogenizing proton beam current of a boron neutron capture treatment system based on a high-current cyclotron. Background BNCT (boron neutron capture therapy) is a precise radiation therapy technology which has rapidly developed in recent years. The basic principle is that the boron-containing medicine is firstly targeted and transported into the patient, and then irradiated by high flux neutrons, so that the boron-10 undergoes a capture reaction and releases high-linearity energy particles, and the highly selective killing of tumor tissues is realized in the cell scale range. In order to obtain enough neutron flux and good irradiation field dose distribution, a clinical BNCT device generally adopts a proton accelerator to bombard a target material to generate neutrons, and a proton beam needs to pass through a beam current transmission and shaping system before entering the target, so that the energy, the position, the section and the time structure of the beam current are precisely controlled. In BNCT systems based on scanning beam expanding homogenization technology, a pair of orthogonally arranged scanning magnets is used for carrying out rapid two-dimensional scanning on a proton beam, and a scanning waveform and a scanning range are reasonably designed to enable the proton beam to form a uniform beam spot similar to a flat top on a target surface, so that local thermal power overload is avoided, and the spatial consistency of irradiation dose is improved. With the increasing requirements of illumination time and spatial uniformity in clinical applications, scanning magnets often need to operate under rapid excitation on the order of hundred Hz while maintaining high uniformity of the integrated field within the good field region. The traditional scanning magnet generally adopts silicon steel sheets or other metal laminations as a magnetic yoke material, and the scanning magnet has good performance under the conditions of lower frequency, continuous or quasi-continuous beam current. However, when the working frequency is raised to the order of hundred Hz and rapid periodic scanning is required, eddy current loss in the metal magnetic yoke increases sharply, which not only leads to a significant increase in the temperature rise of the magnetic yoke, but also introduces significant magnetic field hysteresis and integrated magnetic field uniformity distortion, so that the integrated field is difficult to accurately follow the excitation current variation, and the magnetic field distribution in the good field region is distorted with time. Meanwhile, in the accelerator-based BNCT system (AB-BNCT), accelerators for providing proton sources mainly include electrostatic accelerators, radio frequency linear accelerators, cyclotrons, and the like. These accelerators themselves produce a proton beam which is then used in therapy by bombarding a target material such as lithium, beryllium, etc. Among them, the cyclotron has outstanding advantages in high-power BNCT devices because it can provide continuous, high-current, strong beam current. In particular to BNCT system based on strong current cyclotron, typical proton beam parameters can reach 18 MeV and 1 mA, and beam power is larger. Because the high-power proton beam can cause serious local thermal deposition even if a small amount of beam strikes the vacuum tube wall in the transmission process, and even cause damage or melting of the tube, the system usually needs to use a beam vacuum tube with a larger caliber to improve the transmission safety margin. This further puts forward large aperture design requirements on the scanning magnet, namely, the requirements of magnetic field quality and beam accurate control need to be met under the condition of larger proton beam vacuum aperture, thereby bringing significant engineering design challenges. Therefore, it is necessary to develop a split scanning magnet with small eddy current loss, low temperature rise, fast magnetic field response and high uniformity of integral field aiming at the application requirements of BNCT magnetic scanning system for fast continuous proton beam deflection and high uniformity target surface distribution, so as to meet the higher requirements of clinical radiotherapy on beam scanning precision and stability. Disclosure of Invention Aiming at the defects or improvement demands of the prior art, the invention provides a fast scanning magnet for homogenizing proton beam current of a boron neutron capture treatment system based on a strong current cyclotron, which aims to solve the problems of high temperature rise, slow magnetic field response and integral field uniformity degradation ca