Progress on the development of a proton therapy system based on superconducting cyclotron at HUST Kuanjun Fan Institute of applied electromagnetic engineering Huazhong university of science and technology

OUTLINE Background Wuhan-Proton Therapy Facility Some challenging problems Summary

Urgency of R&D new cancer therapy devices 2016. 08， 全国卫生与健康大会，习近平， “没有全民健康，就没有全面小康” “建设健康环境、发展健康产业为重点，...” Cancer: Leading cause of death in China, major public health problem 20% world’s population; 22% new cancer cases; 27% cancer deaths; 2015, new cases 4.3 million, new deaths 2.8 million; The number is expected to increase continuously because of aging /growth of population; High demand for quality and efficient new cancer treatment methods

Proton therapy(PT) PT: precisely target tumor without harming healthy tissue; PTCOG: more than 131,240 patients have been treated by proton, 67 PT centers in operation, Wanjie 1st PT: Wanjie Hospital in Zibo, IBA, Cyclotron based, with gantry; 2nd PT: Shanghai Proton/Heavy Ion Center (SPHIC) Siemens, Synchrotron based, no gantry Shanghai

China needs domestic PT The rising rates of cancer  fast growing demand for PT facility More than 60 PT centers are in planning or under construction; Almost all from foreign manufactures; (waiting for government permission) Worries: science, technology support the PT boom; Shanghai-PTF Wuhan-PTF Government aims: Develop domestic PT system; Industrialization Two projects are supported by “The national Key R&D program of CN” in 2016 Shanghai-PTF, synchrotron based Wuhan-PTF, SC cyclotron based

OUTLINE Background Wuhan-Proton Therapy Facility Some challenging problems Summary

Wuhan-PTF project HUST organizes a big team to R&D the project R&D management, General system design; Beam transport line, Gantry, nozzle, control system, safety system, IGPT, TPS… PT center construction Clinical experiment, CFDA certificate… Future industrialization of PT system; Superconducting cyclotron

Wuhan-PTF layout Wuhan-PTF One SC cyclotron, one beam line with ESS system, 2 rotating gantries, one fixed treatment rooms, 2 nozzles with pencil beam scanning; Scanning Nozzle 250 MeV/500nA SC-cyclotron Two 360 degree Gantry Fixed treatment room(Hor.+Ver.) Energy degrader and ESS: 70 -250 MeV Beam transport line

Basic parameters of the Wuhan-PTF Maximum energy 250 MeV Aims: Key components, such as SC cyclotron, gantry, Nozzle, transport line… must be developed in China; Complete 80 clinical experiments to obtain CFDA certificate. Energy stability ≤ ±0.1% Energy adjustable range 70-250 MeV Energy adjustment step ≤ 100ms/5 mm Rotation angle Iso-center accuracy ±185° ≤0.5mm Angular speed Gantry 0.1-1rpm adjustable Maximum dose rate ≥3Gy/min Irradiation field 300×300mm

SC-cyclotron CIAE: R&D SC cyclotron features: Parameters: Weight: 90 Tons; Diameter: 3.5 m Max magnetic: 3.2 Tesla; RF cavity number: 4 Beam current: >500 nA; Extraction efficiency: >60% SC cyclotron features: Compact, energy saving, simplicity DC-like beam, high stability and reliability, Ability to modulate beam intensity rapidly and accurately IMPT

Challenging in SC-cyclotron R&D First trial SC cyclotron R&D in China Magnet, RF system, cryostat, cold PIG source, compact central region, extraction, quench protection….

Energy degrader Cyclotrons generate fixed energy, degrader is needed Single wedge Dual wedge Wedge on cylinder Multi-wedge Degrader task: Change energy (250  70 MeV) Material: high density, low atomic number，graphite  boron carbide (B4C)  Fast energy change: 100 ms /5mm step (multi-wedge)

Energy selecting system(ESS) Degrader: Multiple scattering  emittance and momentum spread increases  exceed acceptance Momentum spread  decreases sharpness of Bragg peak; >1% cannot be transported Energy selection system (ESS) is needed Collimator, dipole, energy slit…

Beam transport line Transport line design Transport, intercept and detect 0.1~10 nA p-beam with energy of 70-250 MeV. Adjustment speed t<100 ms / step (5 mm water ) Special care: maximum beam size, possible beam loss, location for beam diagnostics, stability and reproducibility of settings; 恒张力绕线机

Gantry design Isocentric type to provide flexibility Active downstream scanning Large irradiation field (300*300 mm) Small final bending magnet SAD( Source to Isocenter Axis distance) > 2.5 m 360° rotating iso-centric gantry Large inertia, big size, heavy weight Cylinder structure features: High rigidity, angular positioning accuracy, easy to assemble with high accuracy Disadvantage：Heavy

Nozzle with pencil beam scanning Pencil beam scanning nozzle Two magnets deflect the beam to generate a real 3D dose distribution inside the tumor, reduce risks; Features: Spot/lines/contours beam scanning Variable magnetic scan speed

Nozzle with pencil beam scanning Nozzle tasks Detect beam dose, position, size, profile on line.. Control beam deliver and ensure patient safety;

Beam diagnostics system Beam diagnostics is critical for proton Therapy system Tune machine: commissioning/operation Machine safety: MPS Patient treatment: PPS Commissioning Monitoring(position, dose, energy, loss…) Safety Interlock ...  Redundancy robustness is very important Challenges: Small signal with large dynamic range background radiation

Image Guided Proton Therapy system Proton Therapy system Requires accurate localize tumor position Two CBCT are installed on the nozzle oriented at iso-center, More confidence and stability in image quality.  Freedom to capture images from any treatment angle.  Image Guided Proton Therapy CBCT system offers 3D anatomical imaging provide for the most advanced IGPT capabilities.

Control system Control system Machine control: accelerator, beam line, safety… Treatment control: TPS, patient position, medical data access…

Proton therapy center Wuhan PT center: Xiehe (协和) hospital (new campus) 30 km 21

OUTLINE Background Wuhan-Proton Therapy Facility Some challenging problems Summary

Beam extraction from SC cyclotron Superconducting cyclotron High M-field ~3.2 T at extraction Compact size  narrow turn separation at extraction, Limited energy gain by acc. Extraction by electrostatic septum difficult Beam loss at extraction Small turn separation leads to beam loss at ESS Activation, nuclear heating, SC material damage Risk of quench

Precessional resonant extraction Generate first order perturbation at nr=1 using trim rods or coils  beam oscillates around its equilibrium orbit Two consecutive turns oscillate with a slightly different frequency, which increase the phase difference Turn separation increases extraction ↑ Harmonic field

Using a scatter to reduce beam loss Beam loss reduction A small scatter in front of septum to deviate proton beam slightly; Scatter angle optimization: material, position, size…

Energy dependent transmission 4cm 32cm Energy dependence in transmission Transmission varies significantly (0.17%-20% ) Bad dose distribution inside a tumor;

Intensity compensation-1 150 MeV: 2.8 mm 170 MeV: 4.2 mm 190 MeV: 8.2 mm … 230 MeV 12.5 mm Intensity compensation: Mitigate dependence between beam intensity and beam energy De-focussing beam in front of a collimation after ESS

Intensity compensation-2 Defocussing beam in front of a degrader at different beam energy Higher quadeipole

Intensity compensation-3 Fast beam intensity modulation Vert. deflector adjust beam intensity quickly (~50 ms)  IMPT on real time

Summary A SC-cyclotron based PT system is being developed at HUST and CIAE； Many challenging difficulties are expected and must be overcome; Domestic and overseas collaboration is very important;

Summary

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