Akinori Kimura

Verification of the dose distributions with GEANT4 simulation for proton therapy

The GEANT4 based simulation of an irradiation system for the proton therapy has been developed for the verification of dose distributions. The simulation represents a treatment room with the beam irradiation system at the Hyogo Ion Beam Medical Center (HIBMC). The beam irradiation system consists of a lateral beam-spreading system and a range modulating system, so that the dose distribution is achieved in three dimensionally. The simulation was carried out for the proton beams at the isocentric gantry nozzle for the therapeutic energy of 150, 190, and 230 MeV, respectively. The simulated dose distributions are compared with measurements, where dose distributions are obtained using a water phantom at an isocenter, which simulate practical situations of the beam irradiation to the patients. The validation of the simulation was performed for the proton ranges in important materials at beam line and lateral uniformity of the irradiation field at an isocenter, respectively. Then, the dose distribution in simulation based on GEANT4 were verified with measurements for Bragg peak and spread out Bragg peak, respectively. The result of verification shows the depth-dose distributions in simulation are in good agreement with measurements.

GEANT4 based simulation framework for particle therapy system

The particle therapy simulation framework has been developed for radiation therapy using GEANT4 simulation toolkit. The developed simulation framework provides a common interface for composing irradiation systems of different radiation therapy facilities. A particle therapy simulator on the framework represents a treatment room with an irradiation system. Popular beam modifiers for hadron therapy are included in the framework as beam modules and are utilized for composing an irradiation system. The developed framework is designed to be able to customize beam modules as flexible as possible without modifying source codes, because end users such as medical physicists are supposed not to be familiar with developing programming code. Each three types of irradiation systems have been successfully carbon therapy.

Effect of inhomogeneity in a patient's body on the accuracy of the pencil beam algorithm in comparison to Monte Carlo

The pencil beam algorithm (PBA) is reasonably accurate and fast. It is, therefore, the primary method used in routine clinical treatment planning for proton radiotherapy; still, it needs to be validated for use in highly inhomogeneous regions. In our investigation of the effect of patient inhomogeneity, PBA was compared with Monte Carlo (MC). A software framework was developed for the MC simulation of radiotherapy based on Geant4. Anatomical sites selected for the comparison were the head/neck, liver, lung and pelvis region. The dose distributions calculated by the two methods in selected examples were compared, as well as a dose volume histogram (DVH) derived from the dose distributions. The comparison of the off-center ratio (OCR) at the iso-center showed good agreement between the PBA and MC, while discrepancies were seen around the distal fall-off regions. While MC showed a fine structure on the OCR in the distal fall-off region, the PBA showed smoother distribution. The fine structures in MC calculation appeared downstream of very low-density regions. Comparison of DVHs showed that most of the target volumes were similarly covered, while some OARs located around the distal region received a higher dose when calculated by MC than the PBA.

Parallel volume segmentation with tetrahedral adaptive grid

We propose a general-purposed parallel algorithm for volume segmentation, which does not require any prior knowledge on volume nor region. The algorithm provides binary tree structured split-and-merge mechanism to search and localize boundaries along discontinuities and adapts the partition of volume to those detected discontinuities. This algorithm is independent from order of processing or seed selection. And, even though overlapping only one voxel wide boundary between process blocks, by adopting the smoothness-based local feature as homogeneity criteria, consistencies are maintained without overhead of communication between adjacent process blocks. Our efficient hierarchical step-wised mechanism in merging target evaluation makes merge process so simple and efficient that only two brother blocks are considered at each merge step in binary fashion. Experimental results on an artificial and a CT scan volume data are shown.

A Visualization Tool for Geant4-Based Medical Physics Applications

We have been developing a visualization tool for Geant4-based medical physics applications. Geant4 is successfully adapted to radiotherapy, PET and MRT. However, its graphics systems are not suitable for displaying a complex patient data and a dose distribution. In this paper, we describe our visualization tool that supports displaying complex data acquired through the simulation.

The Geant4 Visualisation System – a multi-driver graphics system

From the beginning, the GEANT4 Visualization System was designed to support several simultaneous graphics systems written to common abstract interfaces. Today, it has matured into a powerful diagnostic and presentational tool. It comes with a library of models that may be added to the current scene and which include the representation of the GEANT4 geometry hierarchy, simulated trajectories and user-written hits and digitizations. The workhorse is the OpenGL suite of drivers for X, Xm, Qt, and Win32. There is an Open Inventor driver. Scenes can be exported in special graphics formats for offline viewing in the DAWN, VRML, HepRApp and gMocren browsers. PostScript can be generated through OpenGL, Open Inventor, DAWN and HepRApp. GEANT4s own tracking algorithms are used by the Ray Tracer. Not all drivers support all features but all drivers bring added functionality of some sort. This paper describes the interfaces and details the individual drivers.

Validation of PTSIM for clinical usage

The Geant4 simulation toolkit has been widely accepted in particle therapy domain for more accurate treatment planning. In Japan, the PTSIM, Particle Therapy System Simulation Framework, has been developed by the fund from the Core Research for Evolutional Science and Technology of Japan Science and Technology Agency, JST/CREST. The PTSIM provides a common platform to model beam delivery systems including a DICOM data handling for hadron therapy facility. The PTSIM can simulate existing six irradiation systems in the world and try extending the scope for clinical usage. In this paper, the performance of PTSIM is described for the use of clinical applications as a dose engine. The PTSIM was examined at the National Cancer Center (NCC) and Hyogo Ion Beam Medical Center (HIBMC) in Japan. The dose calculations had been performed on CT images with the treatment parameters determined by a treatment planning system. The dose distributions were compared with pencil beam algorithm.

Visualization for volume data scored by Geant4 simulation

In radiotherapy simulations, Monte Carlo-based radiotherapy simulation is applied to a high accurate calculation of dose distributions in a patient or optimization of the beam delivery system. Geant4 toolkit has come to be utilized to build a Monte Carl simulator for that purpose. It needs the volume rendering capability to display a complex volume data by a visualizer. However, there is no volume rendering capability in the visualization system in Geant4. A volume visualization driver for Geant4 is described in this paper, which is available to display a complex patient image and a dose distribution calculated in a Geant4-based radiotherapy simulation with an external volume visualizer. The volume visualization driver extracts a patient data set, calculated dose distributions, particle trajectories and geometrical information of beam delivery modules in the simulation, and then saves their information as a data file. With that data file, the external volume visualizer is able easily to display results of the simulation.

Requirements in modeling and visualization for Geant4-based radiotherapy simulation

Geant4 is utilized for many radiological software applications and then successfully adopted to them. However, developers spend much time and effort to add functions in order to apply Geant4 to the research of the radiotherapy. We described requirements of the modeling of the target volume such as a patient geometry and the visualization of results in simulation. Additionally, tools we developed subject to the requirements are also described.

Recent updates and plan in Geant4 based particle therapy system simulation framework

Particle therapy system simulation framework, PTSIM, is a simulation framework based on Geant4 Monte Carlo simulation. It has been developed in the project, “Development of simulation framework for advanced radiotherapy”, funded by the Japan Science and Technology Agency (JST) in the program of Core Research for Evolutional Research and Technology (CREST), from 2003 to 2010. The PTSIM has provided a common platform to model proton and ion therapy facilities, allowing users who are not Geant4 experts to accurately and efficiently run Geant4 simulations with the pre-build configurations. Efforts on further development of PTSIM are still under way to include more functionality and improve the performance. The PTSIM has been upgraded with the extensions in the DICOM-RT interface to coordinate with hospital information system, the Web interface with universal grid environment, etc. In this paper, we report on our activities about these updates and plan for extending the PTSIM functionality with new requirements from users.