%#!latexmk proc
\documentclass{CHEP2006}
\setlength{\paperheight}{297mm}
\setlength{\paperwidth}{210mm}

%%
%%  Use \documentclass[boxit]{JAC2003}
%%  to draw a frame with the correct margins on the output.
%%
%%  Use \documentclass[acus]{JAC2003}
%%  for US letter paper layout
%%

\usepackage{graphicx}

%%
%%   VARIABLE HEIGHT FOR THE TITLE BOX (default 35mm)
%%

\setlength{\titleblockheight}{72mm}

\begin{document}
\title{SIMULATION OF HEAVY ION THERAPY SYSTEM USING GEANT4}

%\author{S. Kameoka\thanks{JST-CREST}, T. Sasaki, K. Murakami,\\
%High Energy Accelerator Research Organization (KEK),
%Oho 1-1, Tsukuba 305-0801, Japan\\
%T. Aso, Toyama National College of Maritime Technology,
%1-2 Ebie-Neriya, Imizu-Shi, Toyama 933-0293 Japan\\
%A. Kimura, 268-1 Ohmaecho, Ashikaga-shi, Tochigi 326-8558 Japan\\
%M. Komori, T Kanai, N Kanematsu, Y Kobayashi, S Yonai,
%National Institute of Radiological Sciences (NIRS),
%4-9-1 Anagawa-4-chome, Inage-ku, 263-8555, Chiba-shi, Japan\\
%Y. Kusano, T. Nakajima, O. Takahashi,
%Accelerator Engineering Corporation (AEC),
%2-13-1 Konakadai, 263-0043, Chiba-Inage, Japan\\
%M. Tashiro, Gunma University, Maebashi 371-8512, Japan\\
%Y. Ihara, H. Koikegami, Ishikawa-harima Heavy Industries (IHI),
%TOYOSU IHI BUILDING., 1-1, Toyosu 3-chome, Koto-ku, Tokyo 135-8710, Japan}

\author{S. Kameoka\thanks{JST-CREST}, T. Sasaki$^*$, K. Murakami$^*$,\\
High Energy Accelerator Research Organization (KEK),
Oho 1-1, Tsukuba 305-0801, Japan\\
T. Aso$^*$, Toyama National College of Maritime Technology,
1-2 Ebie-Neriya, Imizu 933-0293 Japan\\
A. Kimura$^*$, Ashikaga Institute of Technology,
268-1 Ohmaecho, Ashikaga 326-8558 Japan\\
M. Komori, T. Kanai, N. Kanematsu, Y. Takei, S. Yonai,
 Institute of Radiological Sciences (NIRS),\\
 4-9-1 Anagawa-4-chome, Inage-ku, Chiba 263-8555, Japan\\
Y. Kusano, T. Nakajima, O. Takahashi,
Accelerator Engineering Corporation (AEC),\\
2-13-1 Konakadai, Inage-ku, Chiba 263-0043, Japan\\
M. Tashiro, Gunma University, Maebashi 371-8512, Japan\\
Y. Ihara, H. Koikegami, Ishikawa-harima Heavy Industries (IHI),\\
TOYOSU IHI BUILDING., 1-1, Toyosu 3-chome, Koto-ku, Tokyo 135-8710, Japan}

\maketitle
%\vspace{2cm}
\begin{abstract}
 We implemented the geometry of 
 a new beamline of HIMAC (Heavy Ion Medical Accelerator in Chiba)
 in Geant4~\cite{Agostinelli:2002hh}, and
 simulated the dose distribution in a water target irradiated with
 carbon beam.
 The simulation well reproduced the Bragg peak
 for the beam energy of 290~MeV and 400~MeV
 while leaving room for improvement in the agreement 
 for the spread-out Bragg peak produced with the ridge filter
 inserted in the beam path.
 This work provides a basis to establish a simulation framework that allows
 comprehensive and accurate treatment planning in heavy ion therapy.
\end{abstract}

\section{Introduction}
Nowadays, effectiveness of heavy ion beam for medical treatment
has been recognized and number of facilities for heavy ion therapy are
in operation or being planned around the world.
Distinct advantage of the heavy ion beam is the capability to
localize dose.
The dose given by a heavy charged particle penetrating matter rises
sharply at the end of the range
while that by a photon beam are maximal near the surface.
This sharp peak in the dose distribution is known as Bragg peak.
If the beam energy is chosen so that the particle stops at the depth of lesion,
the dose can be concentrated on the spot
with minor exposure of adjacent normal tissue.
In addition, heavy ion beam is expected to be effective even aganist
radiation-resistant cells due to higher biological effect
over photon or proton beam.
% higher biological effect over ... is another factor promoting ...

The heavy ion beam involves more complex processes in matter
as compared to photon beam used in conventional radiation therapy.
The heavy ion beam suffers fragmentation into lighter nuclei
with longer ranges, giving tail dose beyond the Bragg peak.
This unwanted dose also needs to be precisely evaluated in treatment planning.
In addition,
taking advantage of the heavy ion beam employs
a variety of instruments specifically designed for the purpose.
To extract such parameters of these instruments %and finely tune the beam
that optimize the clinical effect,
a reliable simulator is essential.
We launched a project aimed at providing a simulation framework for
heavy ion therapy using Geant4.
% paper��refer���Ƥ���Τ�Geant4���������פ�ʤ��Ȼפ��롣

This paper presents the implementation of the geometry of a newly developed
heavy ion beam line of NIRS-HIMAC as a part of the project,
and the validation of the simulator through comparison with experimental data.

\section{BEAMLINE}
HIMAC was constructed at NIRS, national institute of radiological
science in Japan, as the first heavy ion accelerator
dedicated to medical treatment in the world.
Over 2,000 cases have been treated so far and accumulated data
are showing heavy ion therapy to be promising for cancer treatment.

In HIMAC, broad beam method was developed so that
desired volume inside a human body is irradiated with the heavy ion beam.
Fig.~\ref{beamline} shows the beamline instruments and the experimental target
implemented and visualized in the simulation.
The broad beam method combines a pair of dipole magnets (wobbler magnets)
and scattering material
to produce uniform radiation field at treatment position.
The magnetic fields are modulated in such a way that
the beam is moved periodically painting circular-shaped dose distribution.
The detailed description of the wobbler system
is found elsewhere~\cite{komori}.

Secondary emission monitor, installed in front of the wobbler magnets,
consists of parallel aluminum foils enclosed by vacuum windows.
Electrons emanating from the foils are collected
to measure the beam intensity.
The beam line is equipped with two ionization chambers with identical structure
to monitor dose and beam profile.

The Bragg peak is spread by having the beam pass
through a plate made of many ridges (ridge filter)
enough to cover the target thickness.
The ridge filter is designed to flatten the dose over the spread-out Bragg peak
with the biological effectiveness
being ignored specifically for this experiment.

Plates with various thickness~(range shifter) may be inserted in the beam path
to ajust the residual range
although not used in the present experiment.
Lateral beam profile is shaped by collimators.
Multi-leaf collimator is the one with many movable leaves
to change the aperture shape and trim the beam dynamically.
%Finally, range distribution of the beam is modified by a compensator
%to conform to irregular volume.
Note that this beamline was constructed for research and development,
in which the configuration of the components are different from that used in
the actual treatment.

The water in an acrylic vessel was placed at the treatment center (isocenter)
to imitate the human body.
The target was irradiated with $^{12}$C beam and
dose distribution in the water was measured
with multi-channel dosimeter.
In the simulation, the water target was divided into voxels
according to the segmentation of the dosimeter,
and energy deposit in each of them was accumulated.
%
\begin{figure*}[t]
\centering
\includegraphics*[width=145mm,clip]{ihi.eps}
\caption{Heavy ion beam line of HIMAC modeled in Geant4 simiulation}
\label{beamline}
\end{figure*}

\section{SIMULATION}

Geant4 version 8.0 was used in the present work.
Geant4 physics models were configured
to enable ionization, multiple scatternig,
and inelasitc hadronic reactions for ions.
The inelastic reaction is invoked according to the inclusive cross section
based on emprical formulae,
and the rest of the process is treated as intranuclear cascade.
Radioactive decay is invoked when an unstable nucleus is generated.
For secondary particles, available electromagnetic interactions and
hadronic interactions were applied.

\section{RESULTS AND DISCUSSION}

Fig.~\ref{dose290} shows the depth-dose distribution in the water
for the beam energy of 290~MeV/n.
The left figure shows the monochromatic Bragg peak
where the ridge filter was not used.
The right figure shows the spread-out Bragg peak (SOBP) produced
by using the ridge filter.
The Geant4 simulation is shown with solid lines and
the experimental data are plotted with red circles.
The simulated data are fitted to the measured dose curve
with the offset and the scale as parameters.
The fitting resulted in the offset less than the voxel length
in the depth direction (1~mm),
which indicates that the range of the carbon beam in water
is reproduced pretty well.
However the tail dose beyond the Bragg peak seems to be underestimated
in the SOBP.
%to determine whether the slight underestimation in the monochromatic peak
%stack to form clear discrepancy in the SOBP or
%
Further investigation is required to determine whether
the discrepancy is built up of the slight underestimation in the monochromatic
peak or
resulting from the placement of the ridge filter.

The comparison between the simulation and the measurement
for the beam energy of 400~MeV/n
is shown in Fig.\ref{dose400} alike.
Although the spectral shapes are in good agreement with the measurement,
the ranges are found to be underestimated by 1.2~mm and by 2.8~mm
for the monochromatic and the spread-out Bragg peak, respectively.
The different behavior between the enegies of 290~MeV/n and 400~MeV/n
may suggest energy dependent problem of the Geant4 physics models for ions.

\begin{figure*}[htb]
 \begin{minipage}{0.5\linewidth}
  \includegraphics[width=\linewidth,clip]{mono290.eps}
 \end{minipage}
 \begin{minipage}{0.5\linewidth}
  \includegraphics[width=\linewidth,clip]{sobp290.eps}
 \end{minipage}
 \caption{Measured and simulated depth-dose distribution in the water
 irradiated with 290~MeV/n $^{12}$C beam}
 \label{dose290}
\end{figure*}


\begin{figure*}[htb]
 \begin{minipage}{0.5\linewidth}
  \includegraphics[width=\linewidth,clip]{mono400.eps}
 \end{minipage}
 \begin{minipage}{0.5\linewidth}
  \includegraphics[width=\linewidth,clip]{sobp400.eps}
 \end{minipage}
 \caption{Measured and simulated depth-dose distribution in the water
 irradiated with 400~MeV/n $^{12}$C beam}
 \label{dose400}
\end{figure*}


\section{SUMMARY}

We have proposed to utilize Geant4 for the treatment planning
in heavy ion therapy, starting with
the implementation of the new beamline of NIRS-HIMAC in Geant4.
%and simulated the dose measurement in a water target
The Geant4 simulation successfully reproduced the Bragg peaks 
in the water bombarded with $^{12}$C beam
with the energy of 290~MeV/n and 400~MeV/n.
On the other hand,
the tail dose beyond the spread-out Bragg peak produced with 290~MeV/n beam
tends to be underestimated
while the depth of the peak position is slightly underestimated
for 400~MeV/n beam.
We will proceed to improve the simulation capability 
especially for the case where the ridge filter is inserted.
It would be helpful to carry out more thorough experiment
including the identification of secondary particles
to validate the Geant4 physics models for ions in detail.

%\section{ACKNOWLEDGEMENTS}
%
%
%\begin{thebibliography}{9}   % Use for  1-9  references
%%\begin{thebibliography}{99} % Use for 10-99 references
%
%\bibitem{chep04-ref}
%http://www.chep2004.org.
%
%\bibitem{accelconf-ref}
%http://www.JACoW.org.
%
%\bibitem{jacow-help} A. Name and D. Person, Modern Editor.s Journal 25
%(1997) 56.
%
%\bibitem{exampl-ref}
%A.N. Other, ``A Very Interesting Paper'', EPAC'96, Sitges, June 1996.
%
%
%\end{thebibliography}

\bibliography{chervil}
\bibliographystyle{unsrt}

\end{document}
