Simulation of heavy ion therapy system using Geant4

1. Simulation of heavy ion therapy system using Geant4 Satoru Kameoka※1,※2 Takashi SASAKI※1,※2, Koichi MURAKAMI※1,※2, Tsukasa ASO※2※3, Akinori KIMURA※2※4, Masataka KOMORI※5, Tatsuaki KANAI※5, Nobuyuki KANEMATSU※5, Yuka KOBAYASHI※5, Syunsuke YONAI※5, Yousuke KUSANO※6,Takeo NAKAJIMA※6, Osamu TAKAHASHI※6, Mutsumi TASHIRO※7, Yoshihisa IHARA※8, Hajime KOIKEGAMI※8 High Energy Accelerator Research Organization (KEK)※1, CREST JST※2, Toyama National College of Maritime Technology※3, Ashikaga Institute of Technology※4, National Institute of Radiological Sciences※5, Accelerator Engineering Corporation※6, Gunma University※7 Ishikawa-harima Heavy Industries※8

2. Motivation • Background • Effectiveness of Heavy ion beam for cancer treatment • Medical application of heavy ion beam • Complex physics processes • Various specialized instruments • Need for a reliable simulator for treatment planning • Geant4 – toolkit for the simulation of the passage of particle through matter • Objective of this work • Implementation of the geometry of a heavy ion beam line of NIRS-HIMAC • Validation through comparison with experimental data

3. Dose-localizing capability (Bragg peak) High biological effect (cell-killing capability) Beam fragmentation Physical (dis)advantage of heavy ion beam Bragg peak X-ray neutron g-ray Relative dose (%) proton tail Heavy ion Site of cancer Depth of penetration © NIRS

4. Heavy ion therapy (at NIRS-HIMAC) • NIRS – National Institute of Radiological Science (Japan) • HIMAC – Heavy Ion Medical Accelerator in Chiba • First facility for heavy ion therapy in the world • Over 2,000 cases have been treated on trial basis • Broad beam method using wobbler-scatterer system

5. Broad beam method Patient body Collimator Wobbler magnets Ridge Filter Range Shifter Target volume (tumor) X Y Scatterer Beam Compensator (Bolus) By = Ay sin(wt) Bx = Ax sin(wt+p/2) Ridge Filter Bragg peak dose Spread-out Bragg peak Depth

6. General introduction of Geant4 • Toolkit for the simulation of the passage of particle through matter • Designed with object-oriented software technology • Abundant physics models based on experimental data • Powerful capability to describe complex geometry

7. Experimental setup / Geometry implementation in Geant4 simulation Multi-leaf Collimator (open) Acrylic vessel Vacuum window Range shifter (unused) Dose Monitor (ionization Chamber) Water target Collimator Wobber magnets Collimator Scatterer (lead) X Y Beam 12C Beam profile Monitor (ionization Chamber) Ridge filter (aluminum) Treatment position (isocenter) Secondary emission monitor New beam line of NIRS-HIMAC for R & D (overhead view)

8. Target / sensitive detector Water target 2 mm Sensitive region 1 mm 2 mm 400 mm Beam (12C) 300 mm

9. Enabled physics processes in Geant4 • Ions • Electromagnetic interactions • Ionization • Multiple scattering • Inelastic hadronic reaction • Inclusive reaction cross section based on empirical formulae • Intranuclear cascade • Radioactive Decay • Other particles (secondaries) • Electromagnetic interactions • Hadronic interactions

10. Results (12C 290 MeV/n) Spread-out Bragg peak Single Bragg peak w/ Ridge filter wo/ Ridge filter Relative dose Relative dose Depth in water (mm) Depth in water (mm) Offset = - 0.8 mm Offset = -1.0 mm

11. Results (12C 400 MeV/n) Spread-out Bragg peak Single Bragg peak w/ Ridge Filter wo/ Ridge Filter Relative dose Relative dose Depth in water (mm) Depth in water (mm) Offset = -1.2 mm Offset = -2.8 mm

12. Summary • Geometry of the new beamline of NIRS-HIMAC was implemented in Geant4. • (Single) Bragg peak is well reproduced by Geant4 simulation. • Geant4 tends to underestimate the tail dose coming from the beam fragmentation. • To conduct thorough validation of ion physics models of Geant4, comparison with more detailed experiment including the identification of secondary particles is required.

13. Spare OHPs

14. Radiation therapy (of cancer) • Important ‘local treatment’ (as well as surgery) • Photon beam (X-ray or gamma ray) • Flux attenuates exponentially in matter with increasing depth • Unavoidable exposure of surrounding normal tissue limits tolerable dose

15. Horizontal dose profile Relative dose Position (mm)

16. Objective • To establish reliable simulation framework for heavy ion therapy based on Geant4 in order to extract the parameters of specialized instruments to optimize clinical effect (treatment planning) • To implement the geometry of a heavy ion beamline of NIRS-HIMAC in Geant4 and assess the usability of the simulator through comparison with experimental data

17. Instruments for heavy ion therapy • Devices to spread beam laterally • Broad beam method (describe in the next slide …) • Wobbler magnet • Scatterer • Dynamic beam delivery • Devices to shape lateral beam profile • Collimator • Devices to modulate beam range • Range shifter • Ridge filter • Compensator (Bolus) • Dynamic modulation (by accelerator) • Detector • Dosimeter • Beam profile monitor Spot scanning method

18. Wobbler-scatterer system • Wobbler magnets + scatterer + ridge filter

19. Central region Peripheral region Resutls • この絵と一緒に(isocenterでの) beam profileを見せる Beam profile at surface of water target 400 mm 300 mm

20. Implementation of the beamline geometry in the simulation • Show the output of viewer Acrylic vessel water Treatment position (isocenter) Vacuum window Wobbler magnet NIRS-HIMAC