Development of a high resolution voxelised head phantom for medical physics applications

Abstract

Computational anthropomorphic phantoms have become an important investigation tool for medical imaging and dosimetry for radiotherapy and radiation protection. The development of computational phantoms with realistic anatomical features contribute significantly to the development of novel methods in medical physics. For many applications, it is desirable that such computational phantoms have a real-world physical counterpart in order to verify the obtained results. In this work, we report the development of a voxelised phantom, the HIGH_RES_HEAD, modelling a paediatric head based on the commercial phantom 715-HN (CIRS). HIGH_RES_HEAD is unique for its anatomical details and high spatial resolution (0.18 × 0.18 mm2 pixel size). The development of such a phantom was required to investigate the performance of a new proton computed tomography (pCT) system, in terms of detector technology and image reconstruction algorithms. The HIGH_RES_HEAD was used in an ad-hoc Geant4 simulation modelling the pCT system. The simulation application was previously validated with respect to experimental results. When compared to a standard spatial resolution voxelised phantom of the same paediatric head, it was shown that in pCT reconstruction studies, the use of the HIGH_RES_HEAD translates into a reduction from 2% to 0.7% of the average relative stopping power difference between experimental and simulated results thus improving the overall quality of the head phantom simulation. The HIGH_RES_HEAD can also be used for other medical physics applications such as treatment planning studies. A second version of the voxelised phantom was created that contains a prototypic base of skull tumour and surrounding organs at risk.

HDR brachytherapy in vivo source position verification using a 2D diode array: A Monte Carlo study

“…This was achieved by first converting the Hounsfield unit (HU) numbers to a mass density value using a CT–density curve, and then converting from mass density to a material using a look up table . Once imported into the simulation, a geometrical phantom is created, within which is an array of voxels containing the materials (and their compositions) determined from the HU numbers . The compositions and the densities of materials used in the simulations were obtained from the AAPM TG 186 Report .…”

A Geant4 simulation for three-dimensional proton imaging of microscopic samples

“…To broaden the context of this work, it should be mentioned that the Geant4 toolkit has been widely used in the field of macroscopic pCT, either directly or using specific Geant4-based tools suited to medical imaging and radiotherapy, such as GATE (http://www.opengatecollaboration.org) or TOPAS (http://www.topasmc.org). Some of the main topics address the evaluation of the accuracy when determining: (i) dose maps and proton ranges, compared to conventional X-ray scanners [12,13], (ii) relative stopping power, using high spatial resolution voxelized phantoms [14], (iii) individual proton tracking, with the purpose to optimize the experimental setup [15][16] and/or the reconstruction [17,18].…”

The role of Monte Carlo simulation in understanding the performance of proton computed tomography

“…In the case of the simulation of the Phase-II pCT scanner in Geant4, simulation of voxelised phantoms was based on DICOM extended example, which starting from DICOM images of phantoms or patients, converts them into voxelised geometries, typically by employing a stoichiometric calibration from CT values to stopping power. A high-resolution pediatric head phantom [107] was scanned and reconstructed using the Phase-II pCT scanner [105]. It is based on an existing commercially available tissue equivalent pediatric head phantom (model HN715, CIRS, Norfolk, Virginia, USA), and was created by merging eight separate high-resolution helical x-ray CT scans of the physical phantom (pixel size 0.1875 mm × 0.1875 mm).…”