Juan Ignacio Lagares

GAMOS: A Geant4-based easy and flexible framework for nuclear medicine applications

The use of Monte Carlo has proved to be an essential tool in nuclear medicine, to assist in the design of new medical devices, in the development of new image reconstruction algorithms and correction techniques in PET and SPECT, for the precise determination of the dose in radiotherapy, etc. Among the several general-purpose codes, Geant4 is widely used for its modern technology, its flexibility and its wide range of applications. Nevertheless the use of Geant4 in nuclear medicine requires often a long learning-curve that implies a good knowledge of C++ and the Geant4 codes itself to write the code needed to obtain the required results. GAMOS, the Geant4-based Architecture for Medicine-Oriented Simulations, facilitates the use of Geant4 by providing a simple script language that covers almost all the needs of a nuclear medicine simulation. Its modular and flexible design, based on the use of the plug-in technology, as well as a clear documentation and detailed examples, makes easy to extend the framework to cover any extra need an expert user may have. We describe in this paper the basic components of GAMOS as well as provide a few examples of its use in PET and Radiotherapy simulations.

GAMOS: An easy and flexible way to use GEANT4

The wide range of physics models available in GEANT4, as well as its outstanding geometry and visualization tools, has made it gain widespread use in several fields of physics, like high energy, medical, space, etc. Nevertheless the use of GEANT4 often requires a long learning-curve, which implies a good knowledge of C++ and the GEANT4 code itself. GAMOS facilitates the use of GEANT4 by avoiding the need to use C++, providing instead a set of user commands. One of the novelties of GAMOS with respect to similar simulation codes lies in its flexibility, which makes it appropriate for simulation in many physics fields. This flexibility is sustained by the wide range of geometrical configurations, primary generators and physics lists supported and by the comprehensive set of tools that help the user in extracting detailed information from the simulation through user commands. The use of the plug-in technology contributes to this flexibility, as it facilitates the extension of the framework to include extra functionality not foreseen by the framework authors. GAMOS counts already with several hundreds registered users in the five continents; while it is more frequently used in the medical physics field, its use has also been extended to other fields, like high energy physics, space physics, neutron shielding, etc.

Neutron spectra around a tandem linear accelerator in the generation of 18F with a bonner sphere spectrometer

A Bonner sphere spectrometer was used to measure the neutron spectra produced at the collision of protons with an H2(18)O target at different angles. A unique H2(18)O target to produce (18)F was designed and placed in a Tandem linear particle accelerator which produces 8.5MeV protons. The neutron count rates measured with the Bonner spheres were unfolded with the MAXED code. With the GEANT4 Monte Carlo code the neutron spectrum induced in the (p, n) reaction was estimated, this spectrum was used as initial guess during unfolding. Although the cross section of the reaction (18)O(p,n)(18)F is well known, the neutron energy spectra is not correctly defined and it is necessary to verify the simulation with measurements. For this reason, the sensitivity of the unfolding method to the initial spectrum was analyzed applying small variation to the fast neutron peak.

Production of [11C]CO2 with gas target at low proton energies.

Nowadays the demand and the installation of self-shielded low-energy cyclotrons is growing, allowing the use of (11)C in many more centers. The aim of this study was the design of a new target and the evaluation of the production of (11)C as [(11)C]CO2 at low proton energies. The target was coupled to an IBA Cyclone-18/9 and the energy was decreased to 4-16 MeV. The newly designed target allowed the production of [(11)C]CO2 at different proton energies, and the results suggest that the cyclotron energy of Cyclone-18/9 is slightly higher than the nominal 18 MeV.

Anew physics model for the charged particle transport with Geant4

An accurate modeling of the interactions of charged particles (protons, 2H, 3H, 3He, α-particles…) with energies up to tenths of MeV is necessary for many physical problems and applications such as proton therapy or isotope production for medical imaging (e.g. 11C and 18F), activation calculations, accelerator shielding or material damage calculations. Most of the Monte Carlo simulation codes, and in particular the Geant4 simulation package, applied to these types of problems do rely on theoretical nuclear models rather than evaluated cross section data. It is well known that the validity of nuclear models used in Monte Carlo codes for describing the interaction of charged particles in the energy range up to tenths of MeV can be poor and lead to unacceptably large systematic uncertainties if the model parameters are not adjusted by comparison to experimental data. For this reason, we have developed the G4ParticleHP package for Geant4. The package allows simulating the interaction of charged particles interactions using evaluated nuclear data libraries for charged particles such as ENDF-B.VII or TENDL.

Calculation by GAMOS/Geant4 simulation of cellular energy distributions from alpha and lithium-7 particles created by BNCT

Monte Carlo (MC) has demonstrated to be a suitable technique to evaluate the microdosimetric parameters at the cellular level for Boron Neutron Capture Therapy (BNCT). The objectives of the current study are first to validate GAMOS MC codes with different Geant4 physics models for the range calculations of alpha particles. Once the proper physics is selected, the second objective is to determine the distributions of deposited energy in cellular medium originated by alpha and lithium-7 particles induced by 10B(n,α)7Li.

A utility to read automatically DICOM format data for GAMOS/Geant4 simulation

Introduction The simulation of a real clinical radiotherapy treatment requires using the detailed information about patient, acceleration and plan. Modern machines can provide this information in DICOM format, but Monte Carlo codes are not able to treat it. Purpose To provide a tool to automatically read the data on patient anatomy, including RT structures, and the RT plan parameters and prepare the corresponding Monte Carlo jobs. Materials and methods We have developed in GAMOS/Geant4 framework a set of tools based on DCMTK to read a patient anatomy in DICOM format and transform the Hounsfield values into Geant4 materials. The DICOM RT Structure files are also read and combined with the anatomy to identify the voxels that are included in each structure. Another tool converts the many parameters of a RT plan into Monte Carlo parameters. Several utilities help the user check for the correct interpretation of the DICOM parameters. Results The tool has been applied to read many different DICOM patient anatomies from different providers. A full radiotherapy treatment has been simulated and the dose calculated and written in DICOM format has been compared with the one obtained using the vendor TPS. Conclusion A simple way is provided to automatically convert a radiotherapy treatment in DICOM format to GAMOS/Geant4 parameters so that real clinical treatments can be easily simulated.