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Pham T.,University of Connecticut | Deherrera M.,Edwards Group | Sun W.,University of Connecticut
Computer Methods in Biomechanics and Biomedical Engineering | Year: 2014

Recent clinical studies of the percutaneous transvenous mitral annuloplasty (PTMA) devices have shown a short-term reduction of mitral regurgitation after implantation. However, adverse events associated with the devices such as compression and perforation of vessel branches, device migration and fracture were reported. In this study, a finite element analysis was carried out to investigate the biomechanical interaction between the proximal anchor stent of a PTMA device and the coronary sinus (CS) vessel in three steps including: (i) the stent release and contact with the CS wall, (ii) the axial pull t the stent connector and (iii) the pressure inflation of the vessel wall. To investigate the impact of the material properties of tissues and stents on the interactive responses, the CS vessel was modelled with human and porcine material properties, and the proximal stent was modelled with two different Nitinol materials with one being stiffer than the other. The results indicated that the vessel wall stresses and contact forces imposed by the stents were much higher in the human model than the porcine model. However, the mechanical differences induced by the two stent types were relatively small. The softer stent exhibited a better fatigue safety factor when deployed in the human model than in the porcine model. These results underscored the importance of the CS tissue mechanical properties. Vessel wall stress and stent radial force obtained in the human model were higher than those obtained in the porcine model, which also brought up questions as to the validity of using the porcine model to assess device mechanical function. The quantification of these biomechanical interactions can offer scientific insight into the development and optimisation of the PTMA device design. © 2013 © 2013 Taylor & Francis. Source

Pinkham M.B.,University of Manchester | Pinkham M.B.,University of Queensland | Sanghera P.,Edwards Group | Wall G.K.,Neuropsychology | And 2 more authors.
Clinical Oncology | Year: 2015

About 90% of patients with brain metastases have impaired neurocognitive function at diagnosis and up to two-thirds will show further declines within 2-6 months of whole brain radiotherapy. Distinguishing treatment effects from progressive disease can be challenging because the prognosis remains poor in many patients. Omitting whole brain radiotherapy after local therapy in good prognosis patients improves verbal memory at 4 months, but the effect of higher intracranial recurrence and salvage therapy rates on neurocognitive function beyond this time point is unknown. Hippocampal-sparing whole brain radiotherapy and postoperative stereotactic radiosurgery are investigational techniques intended to reduce toxicity. Here we describe the changes that can occur and review technological, pharmacological and practical approaches used to mitigate their effect in clinical practice. © 2015 The Royal College of Radiologists. Source

Sanghera P.,Edwards Group | Rampling R.,Beatson West of Scotland Cancer Center | Haylock B.,Clatterbridge Center for Oncology | Jefferies S.,Addenbrookes Hospital | And 4 more authors.
Clinical Oncology | Year: 2012

Since postoperative radiotherapy plus concomitant temozolomide followed by adjuvant temozolomide has become standard treatment for glioblastoma, the phenomenon of early post-treatment enlargement of the imaged tumour volume, usually without clinical deterioration, has become widely recognised. The term pseudoprogression has been used to describe a poorly understood pathophysiological process. In this review, the pathophysiological concepts, relevance, diagnosis and management of patients with 'pseudoprogression' and 'pseudoresponse' are discussed. Guidelines are given with respect to radiological imaging modality, mode and frequency. Further biological and clinical insights into these phenomena require carefully designed prospective studies. © 2011 The Royal College of Radiologists. Source

Chalkley A.,Edwards Group
The British journal of radiology | Year: 2014

To evaluate a new commercial PTW-60019 microDiamond (PTW, Freiburg, Germany) synthetic single-crystal diamond detector for relative dosimetry measurements on a clinical CyberKnife™ VSI (Accuray Inc., Sunnyvale, CA) system. Relative output factors (ROFs) were measured for collimator diameters from 5 to 60 mm, and compared with diode [PTW-60017, PTW-60018 and IBA Dosimetry (Schwarzenbruck, Germany) SFD] and ionization chamber (PTW-31014 PinPoint and PTW-31010 Semiflex) measurements. Beam profiles were measured at a range of depths, and collimator sizes, with the detector stem oriented both parallel and perpendicular to the central axis (CAX). Percentage depth-dose (PDD) curves were obtained for the 60-mm collimator and compared with natural Diamond Detector (PTW-60003) and ionization chamber curves to evaluate energy dependence. Penumbral broadening was noted on profile measurements made with the microDiamond oriented with the stem parallel to the CAX, in comparison with diodes. Oriented perpendicular to the CAX, the profile penumbra was sharper, but stem effects could not be ruled out. The PDD measurements were within 0.5% of ionization chamber measurements, indicating insignificant dose-rate dependence. The ROF for the microDiamond fell between diode and ionization chamber results. Published Monte Carlo-derived CyberKnife-specific factors were applied to the PTW-60017, PTW-60018 and PTW-31014 ROFs, and the microDiamond factors agreed within 2.0% of the mean of these. Over a range of small field relative dosimetry measurements, the microDiamond detector shows excellent spatial resolution, dose-rate independence and water equivalence. The microDiamond is a suitable tool for commissioning stereotactic systems. Source

Hartley A.,Edwards Group | Sanghera P.,Edwards Group | Kazi W.,Edwards Group | Mehanna H.,Coventry University | And 3 more authors.
Clinical Oncology | Year: 2011

Aims: There has been a resurgence in interest in radiobiological modelling in head and neck cancer. The aim of this study was to determine if currently used parameters accurately predict both tumour and toxicity outcomes. Materials and methods: Trials were identified from a recent meta-analysis of altered fractionation. The tumour biologically effective dose (tBED; α/β=10Gy, tk [onset time of accelerated repopulation]=22 days, tp [average doubling time during accelerated repopulation]=3 days, α=0.3Gy-1), acute mucosal biologically effective dose (amBED; α/β=10Gy, tk=7 days, tp=2.5 days, α=0.3Gy-1) and late mucosal biologically effective dose (lmBED; α/β=3Gy) were calculated for each arm of each trial. The correlation between the absolute percentage difference in BED between treatment arms and the observed percentage difference in local control, acute grade 3 mucositis and late grade 3 mucosal reaction was then assessed. Results: A strong correlation was observed between the percentage difference in tBED and the percentage difference in local control (P=0.006). A trend towards a correlation was seen between the percentage difference in amBED and the percentage difference in acute grade 3 mucositis (P=0.06). A significant correlation was observed between the percentage difference in lmBED and the percentage difference in grade 3 late mucosal toxicity (P=0.02). However, a 15% decrease in lmBED between control and experimental arms of the study was necessary for any sparing of late mucosal toxicity to be observed. Conclusions: Currently used parameters for tumour accurately predict outcomes in randomised trials of altered fractionation. Although the relationship may be more complex for late mucosal reaction, the presence of a correlation is noteworthy given the infrequent reporting or occurrence of this toxicity. In the future, radiobiological modelling with the addition of volumetric parameters will be highly relevant, given attempts to dose escalate with intensity-modulated radiotherapy in poor risk patients and de-escalate in patients with an excellent prognosis. © 2010 The Royal College of Radiologists. Source

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