Simulation of heavy ion therapy system using Geant4

Satoru Kameoka 1, 2※ ※ Takashi SASAKI 1, 2, Koichi MURAKAMI 1, 2, Tsukasa ASO 2 3, Ak※ ※ ※ ※ ※ ※inori KIMURA 2 4, Masataka KOMORI 5, Tatsuaki KANAI 5, Nobuyuki K※ ※ ※ ※ANEMATSU 5, Yuka KOBAYASHI 5, Syunsuke YONAI 5, Yousuke KUS※ ※ ※ANO 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, Ashika※ ※ga Institute of Technology 4, National Institute of Radiological Sciences 5, ※ ※

Accelerator Engineering Corporation 6, Gunma University 7※ ※Ishikawa-harima Heavy Industries 8 ※

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

Physical (dis)advantage of heavy ion beam

• Dose-localizing capability (Bragg peak)

• High biological effect (cell-killing capability)

• Beam fragmentation

Site of cancer © NIRSDepth of penetration

Rel

ativ

e do

se (

%)

proton

Heavy ion

X-ray

-ray neutron

tail

Bragg peak

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 basi

s• Broad beam method using wobbler-scatterer sys

tem

Broad beam method Patient body

Wobbler magnets

YX

Ridge Filter

Scatterer

RangeShifter

Collimator

Compensator(Bolus)

Target volume(tumor)

Bragg peak

Spread-outBragg peak

Depth

dose

Beam

RidgeFilter

By = Ay sin(t)

Bx = Ax sin(t+/2)

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

Experimental setup / Geometry implementation in Geant4 simulation

Treatment position(isocenter)

Vacuum window

Watertarget

Acrylicvessel

New beam line of NIRS-HIMAC for R & D(overhead view)

Secondary emissionmonitor

Wobber magnets

X Y Scatterer(lead)

DoseMonitor

(ionization Chamber)

Collimator

Ridge filter(aluminum)

Range shifter(unused)

Multi-leafCollimator

(open)

Collimator

Beam profileMonitor

(ionizationChamber)

Beam12C

Target / sensitive detector

400 mm

300 mm

2 mm

1 mm

2 mmWatertarget

Beam (12C)

Sensitive region

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

Results (12C 290 MeV/n)

w/ Ridge filterwo/ Ridge filter

Offset = - 0.8 mm Offset = -1.0 mm

Single Bragg peak Spread-out Bragg peak

Depth in water (mm) Depth in water (mm)

Re

lativ

e d

ose

Re

lativ

e d

ose

Results (12C 400 MeV/n)

Offset = -1.2 mm Offset = -2.8 mm

w/ Ridge Filterwo/ Ridge Filter

Single Bragg peak Spread-out Bragg peak

Depth in water (mm) Depth in water (mm)

Re

lativ

e d

ose

Re

lativ

e d

ose

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.

Spare OHPs

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

Horizontal dose profile

Position (mm)

Rel

ativ

e do

se

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

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

Wobbler-scatterer system

• Wobbler magnets + scatterer + ridge filter

Resutls

• この絵と一緒に (isocenter での ) beam profile を見せる

Centralregion

Peripheralregion

Beam profile at surface of water target

400 mm

300 mm

Implementation of the beamline geometry in the simulation

• Show the output of viewer

Treatment position(isocenter)

Wobbler magnet

Vacuum window

waterAcrylicvessel

NIRS-HIMAC