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1.
Phys Imaging Radiat Oncol ; 28: 100506, 2023 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-38045641

RESUMO

Background and purpose: Accurate dosimetry in Ultra-High Dose Rate (UHDR) beams is challenging because high levels of ion recombination occur within ionisation chambers used as reference dosimeters. A Small-body Portable Graphite Calorimeter (SPGC) exhibiting a dose-rate independent response was built to offer reduced uncertainty on secondary standard dosimetry in UHDR regimes. The aim of this study was to quantify the effect of the geometry and material properties of the device on the dose measurement. Materials and methods: A detailed model of the SPGC was built in the Monte Carlo code TOPAS (v3.6.1) to derive the impurity and gap correction factors, kimp and kgap. A dose conversion factor, DwMC/DgMC, was also calculated using FLUKA (v2021.2.0). These factors convert the average dose to its graphite core to the dose-to-water for a 249.7 MeV mono-energetic spot-scanned clinical proton beam. The effect of the surrounding Styrofoam on the dose measurement was examined in the simulations by substituting it for graphite. Results: The kimp and kgap correction factors were 0.9993 ± 0.0002 and 1.0000 ± 0.0001, respectively when the Styrofoam was not substituted, and 1.0037 ± 0.0002 and 0.9999 ± 0.0001, respectively when substituted for graphite. The dose conversion factor was calculated to be 1.0806 ± 0.0001. All uncertainties are Type A. Conclusions: Impurity and gap correction factors, and the dose conversion factor were calculated for the SPGC in a FLASH proton beam. Separating out the effect of scatter from Styrofoam insulation showed this as the dominating correction factor, amounting to 1.0043 ± 0.0002.

2.
Sci Rep ; 13(1): 2054, 2023 02 04.
Artigo em Inglês | MEDLINE | ID: mdl-36739297

RESUMO

A paradigm shift is occurring in clinical oncology exploiting the recent discovery that short pulses of ultra-high dose rate (UHDR) radiation-FLASH radiotherapy-can significantly spare healthy tissues whilst still being at least as effective in curing cancer as radiotherapy at conventional dose rates. These properties promise reduced post-treatment complications, whilst improving patient access to proton beam radiotherapy and reducing costs. However, accurate dosimetry at UHDR is extremely complicated. This work presents measurements performed with a primary-standard proton calorimeter and derivation of the required correction factors needed to determine absolute dose for FLASH proton beam radiotherapy with an uncertainty of 0.9% (1[Formula: see text]), in line with that of conventional treatments. The establishment of a primary standard for FLASH proton radiotherapy improves accuracy and consistency of the dose delivered and is crucial for the safe implementation of clinical trials, and beyond, for this new treatment modality.


Assuntos
Neoplasias , Terapia com Prótons , Humanos , Prótons , Dosagem Radioterapêutica , Radiometria , Neoplasias/radioterapia
3.
Colloids Surf B Biointerfaces ; 161: 677-687, 2018 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-29175762

RESUMO

While stainless steel is a broadly used alloy with interesting mechanical properties, its applications in medicine suffers from inherent biocompatibility limitations. An attractive opportunity to improve its performance is to alter its surface, but this has proven challenging. We now show how high range anodization conditions using H2SO4/H2O2 as an atypical electrolyte can efficiently nanocavitate the surface of both stainless steel SS304 and SS316 and create a topography with advantageous biomedical characteristics. We describe the structural and chemical features of the resulting surfaces, and propose a nanocorrosion/transpassivation/repassivation mechanism for its creation. Our approach creates a thin mesoporous layer of crystalline oxide that selectively promotes mammalian cell activity and limits bacterial adhesion. The modified surfaces favor the formation and maturation of focal adhesion plaques and environment-sensing filopodia with abundant extra small lateral membrane protrusions, suggesting an increase in membrane fluidity. These protrusions represent a yet undescribed cellular response. Such surfaces promise to facilitate the integration of implantable SS devices, in general. In addition, our strategy simultaneously provides a simple, commercially attractive way to control the adhesion of microorganisms, making nanostructured stainless steel broadly useful in hospital environments, in manufacturing medical devices, as well as offering possibilities for non-medical applications.


Assuntos
Materiais Revestidos Biocompatíveis/química , Eletrólitos/química , Nanoestruturas/química , Aço Inoxidável/química , Animais , Aderência Bacteriana/efeitos dos fármacos , Adesão Celular/efeitos dos fármacos , Linhagem Celular , Materiais Revestidos Biocompatíveis/farmacologia , Técnicas Eletroquímicas/métodos , Peróxido de Hidrogênio/química , Camundongos , Microscopia de Força Atômica , Células NIH 3T3 , Nanoestruturas/ultraestrutura , Porosidade , Ácidos Sulfúricos/química , Propriedades de Superfície
4.
BMJ ; 327(7425): s164-5, 2003 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-14630786
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