1. 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

2. OUTLINE
Background
Wuhan-Proton Therapy Facility
Some challenging problems
Summary

3. Urgency of R&D new cancer therapy devices
， 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

4. 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

5. 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

6. OUTLINE
Background
Wuhan-Proton Therapy Facility
Some challenging problems
Summary

7. 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

8. 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: MeV
Beam transport line

9. 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
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

10. 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

11. 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….

12. 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)

13. 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…

14. Beam transport line Transport line design
Transport, intercept and detect 0.1~10 nA p-beam with energy of 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

15. 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

16. 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

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

18. 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

19. 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.

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

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

22. OUTLINE
Background
Wuhan-Proton Therapy Facility
Some challenging problems
Summary

23. 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

24. 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

25. 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…

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

27. 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

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

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

30. 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;

31. Summary

32. Thank you!