Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Monte Carlo (MC) codes serve as the gold standard simulation tool during design and optimisation of x-ray imaging systems. Such simulations often model Rayleigh scattering based on the Independent Atom Approximation Model (IAM). This model neglects the low range molecular interference (MI) effects of non-crystalline materials such as human tissues. Previous work has found discrepancies in the simulated images of planar x-ray images between IAM and MI models. However, insignificant differences were found for computed tomography (CT) reconstructions. In this work we present Geant4 MC simulations of a flat panel source digital tomosynthesis (DT) system for human extremities. Results show that with a 1:9 scatter to primary ratio (SPR) in the x-ray projections, the DT reconstructions are insensitive to the differences of the IAM and MI models. Therefore, MC codes that use the IAM model are sufficient for the study of DT systems. That is because DT algorithms have a larger effect on image quality than the few percent change in the noise due to a physical model and noise suppression methods make this change even less important. Dependency of this conclusion on SPR must be considered in other DT modalities where SPR might be larger.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Brachytherapy is a common treatment in cervical, uterine and vaginal cancer management. The technique is characterised by rapid developments in the fields of medical imaging, dosimetry planning and personalised medical device design. To reduce unnecessary burden on patients, assessments and training of these technologies should preferable be done using high-fidelity physical phantoms. In this study, anthropomorphic deformable phantoms of the vaginal wall and cavity were developed for image-guided adaptive brachytherapy, in which vaginal wall biomechanics were mimicked. Phantoms were produced from both silicone and polyvinyl alcohol materials. Material characterisations were performed with uniaxial tensile tests, via which Young’s moduli and toughness were quantified. In addition, the contrast between adjacent phantom layers was quantified in magnetic resonance images. The results showed that stress-strain curves of the silicone phantoms were within the range of those found in healthy human vaginal wall tissues. Sample preconditioning had a large effect on Young’s moduli, which ranged between 2.13 and 6.94 MPa in silicone. Toughness was a more robust and accurate metric for biomechanical matching, and ranged between 0.23 and 0.28 ·10<jats:sup>6</jats:sup> J·m<jats:sup>−3</jats:sup> as a result of preconditioning. The polyvinyl alcohol phantoms were not stiff or tough enough, with a Young’s modulus of 0.16 MPa and toughness of 0.02 ·10<jats:sup>6</jats:sup> J·m<jats:sup>−3</jats:sup>. All materials used could be clearly delineated in magnetic resonance images, although the MRI sequence did affect layer contrast. In conclusion, we developed anthropomorphic deformable phantoms that mimic vaginal wall tissue and are well visible in magnetic resonance images. These phantoms will be used to evaluate the properties and to optimise the development and use of personalised brachytherapy applicators.</jats:p>