Monte Carlo simulation of a realistic anatomical phantom described by triangle meshes: Application to prostate brachytherapy imaging

Abstract

Purpose-Monte Carlo codes can simulate the transport of radiation within matter with high accuracy and can be used to study medical applications of ionising radiations. The aim of our work was to develop a Monte Carlo code capable of generating projection images of the human body. In order to obtain clinically realistic images a detailed anthropomorphic phantom was prepared. These two simulation tools are intended to study the multiple applications of imaging in radiotherapy, from image guided treatments to portal imaging.Methods-We adapted the general purpose code PENELOPE 2006 to simulate a radiation source, an ideal digital detector, and a realistic model of the patient anatomy. The anthropomorphic phantom was developed using computer-aided design tools, and is based on the NCAT phantom. The surface of each organ is modelled using a closed triangle mesh, and the full phantom contains 330 organs and more than 5 million triangles. A novel object-oriented geometry package, which includes an octree structure to sort the triangles, has been developed to use this complex geometry with PENELOPE.Results-As an example of the capabilities of the new code, projection images of the human pelvis region were simulated. Radioactive seeds were included inside the phantom's prostate. Therefore, the resulting simulated images resemble what would be obtained in a clinical procedure to assess the positioning of the seeds in a prostate brachytherapy treatment.Conclusions-The new code can produce projection images of the human body that are comparable to those obtained by a real imaging system (within the limitations of the anatomical phantom and the detector model). The simulated images can be used to study and optimise an imaging task (i.e., maximise the object detectability, minimise the delivered dose, find the optimum beam energy, etc.). Since PENELOPE can simulate radiation from 50 eV to 1 GeV, the code can also be used to simulate radiotherapy treatments and portal imaging. Using the octree data structure, the new Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript geometry model does not significantly increase the computing time when compared to the simulation of a much simpler quadric geometry. In conclusion, we have shown that it is feasible to use PENELOPE and a complex triangle mesh geometry to simulate real medical physics applications.

Determination of absorbed dose in water at the reference point for an HDR brachytherapy source using a Fricke system

“…Aspects related to both condensed and mixed simulation schemes and reduction in computing time have been described by Salvat et al 21 This MC has been used extensively for simulation of brachytherapy sources. [22][23][24][25][26][27] Photons were simulated until their energy fell below 10 keV. At the energy used in this study, it has been verified previously 13 and in our own calculation that it is not necessary to follow the electrons.…”

penMesh—Monte Carlo Radiation Transport Simulation in a Triangle Mesh Geometry

“…Triangle meshes can approximate any arbitrary surface and, therefore, can represent the boundary of virtually any object. PenMesh has been successfully employed in the past to study two medical imaging applications: coronary angiography [8], [9] and prostate brachytherapy imaging [10]. Other MC codes have also been extended to CAD geometries, such as GEANT [11] or EGS4 [12].…”

“…The simulation code penMesh [7]- [10] implements a general-purpose MC algorithm that simulates the transport of electrons, positrons and photons in a geometry composed of homogeneous bodies limited by triangle meshes. The interaction between matter and radiation, in the energy range from 50 to 1 GeV, is simulated by the state-of-the-art physics subroutines from the PENELOPE 2006 package [1].…”

Realistic X-ray CT simulation of the XCAT phantom with SINDBAD

“…They either propose analytical [3] or Monte Carlo approaches [4] to model the X-ray image generation. SINDBAD both combine the advantages of these two different approaches in order to quickly provide simulated images including both primary and scatter components.…”