General Purpose Transistor Characterized as Dosimetry Sensor of Proton Beams

A commercial pMOS transistor (MOSFET), 3N163 from Vishay (USA), has been characterized as a low-energy proton beam dosimeter. The top of the samples' housing has been removed to guarantee that protons reached the sensitive area, that is, the silicon die. Irradiations took place at the National Accelerator Centre (Seville, Spain). During irradiations, the transistors were biased to improve the sensitivity, and the silicon temperature was monitored activating the parasitic diode of the MOSFET. Bias voltages of 0, 1, 5, and 10 V were applied to four sets of three transistors, obtaining an averaged sensitivity that was linearly dependent on this voltage. In addition, the short-fading effect was studied, and the uncertainty of this effect was obtained. The bias voltage that provided an acceptable sensitivity, (11.4 ± 0.9) mV/Gy, minimizing the uncertainty due to the fading effect (-0.09 ± 0.11) Gy was 1 V for a total absorbed dose of 40 Gy. Therefore, this off-the-shelf electronic device presents promising characteristics as a dosimeter sensor for proton beams.

Monte Carlo calculation of charge collection efficiencies in ionization chambers

Collection efficiency is an important quantity in dosimetry with ionization chambers. It can be calculated by solving a hyperbolic system of partial differential equations. This system can be solved only in few, simple, idealized geometries, but for more realistic designs an analytical resolution is no longer possible. In the present work a Monte Carlo scheme that could permit to calculate the collection efficiency for any ionization chamber geometry is proposed. This scheme has been tested against Boag's approach for three chambers with plane-parallel, cylindrical and spherical geometries, operated in the recombination regime. The results obtained in the full Monte Carlo simulation closely agree with the Boag's ones for the three ideal geometries considered. The largest relative difference, ∼0.3%, has been found for the plane-parallel chamber in case of 50 V, the lowest potential difference investigated in this study. Results appear to be stable against changes in the chamber volume, the ion mobility and the recombination constant. The method proposed could be a useful tool to calculate collection efficiencies of ionization chambers, provided the electric field inside them is known.

Abstract 178: Quantification of matrix remodeling during H1299 lung cancer cell migration in microfluidic devices

Introduction

Metastasis is a hallmark of cancer and represents a major clinical challenge. Since cell migration is a key process for metastasis, it is of great importance to understand the mechanisms of cancer cell migration. In the last decade, novel microfluidic devices, containing extracellular matrix (ECM) biomimetic hydrogels, have become attractive tools to recapitulate the tumor microenvironment, thus permitting the study of cancer cell migration in a more physiological 3D environment.

Previously, we have used microfluidic platforms, filled with hydrogels of mixed collagen-Matrigel composition, to investigate the effect of the microenvironment on H1299 NSCLC migration, and demonstrated how the biomechanical properties of the hydrogels determined the phenotype and migration speed of the cells. We concluded that a balanced composition of collagen and Matrigel favors cell migration, due to an increased matrix stiffness and pore size of the hydrogels.

Objectives

To further examine the impact of the ECM on cell migration, we now quantify matrix remodeling due to metalloproteinase (MMP) activity during H1299 migration, in mixed collagen-Matrigel hydrogels. Our second goal is to study the relationship between H1299 cancer cell migration and H1299 integrin expression levels in the same hydrogels, to understand how integrin profile is modulated by hydrogel composition.

Methods

We used three different hydrogels with the same collagen concentration of 2 mg/ml and 0 (C), 2 (CM) and 4 (CM+) mg/ml of Matrigel respectively. Proteolytic degradation of hydrogel caused during H1299 cell migration was quantified as the volume of a dye-quenched protein substrate (DQ collagen I) at 25 µg/ml, imaged by confocal microscopy (40X) and measured using in-house developed image analysis tools.

β1 and β3 integrin expression at cell surface was quantified by flow cytometry after stimulating cell migration inside the hydrogels for 24 h.

Results

The DQ volume per cell ratio revealed the proteolytic degradation was ~5 times higher in Matrigel-containing hydrogels CM and CM+ than in collagen-only hydrogel C. Cytometry assays showed β1 integrin is expressed by H1299 cells significantly more than β3 integrin in all three hydrogels. Moreover, we found β1 integrin expression at cell surface was higher in CM and CM+ hydrogels than in C hydrogels.

Conclusions

Hydrogel composition modifies H1299 integrin profile at cell surface. Accordingly, β1 integrin expression is higher than β3 integrin expression in all hydrogels studied as a result of collagen type I being the main binding ligand to β1 integrin.

Matrigel, at an intermediate, balanced concentration, enhances cell migration by stimulating both integrin expression at cell surface and matrix degradation due to MMP activity, thus compensating the higher degree of cell confinement compared to collagen-only hydrogels.

Citation Format: Maria Anguiano, Xabier Morales, Mikel Ariz, Martín Martínez Villar, Carlos Ortiz-de-Solorzano. Quantification of matrix remodeling during H1299 lung cancer cell migration in microfluidic devices [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 178.

Characterization of the role of collagen network structure and composition in cancer cell migration

The geometry of 3D collagen networks is a key factor that influences the behavior of live cells within extra-cellular matrices. This paper presents a method for automatic quantification of the 3D collagen network geometry with fiber resolution in confocal reflection microscopy images. The proposed method is based on a smoothing filter and binarization of the collagen network followed by a fiber reconstruction algorithm. The method is validated on 3D collagen gels with various collagen and Matrigel concentrations. The results reveal that Matrigel affects the collagen network geometry by decreasing the network pore size while preserving the fiber length and fiber persistence length. The influence of network composition and geometry, especially pore size, is preliminarily analyzed by quantifying the migration patterns of lung cancer cells within microfluidic devices filled with three different hydrogel types. The experiments reveal that Matrigel, while decreasing pore size, stimulates cell migration. Further studies on this relationship could be instrumental for the study of cancer metastasis and other biological processes involving cell migration.

Ex Vivo Profiling of PD-1 Blockade Using Organotypic Tumor Spheroids

Ex vivo systems that incorporate features of the tumor microenvironment and model the dynamic response to immune checkpoint blockade (ICB) may facilitate efforts in precision immuno-oncology and the development of effective combination therapies. Here, we demonstrate the ability to interrogate ex vivo response to ICB using murine- and patient-derived organotypic tumor spheroids (MDOTS/PDOTS). MDOTS/PDOTS isolated from mouse and human tumors retain autologous lymphoid and myeloid cell populations and respond to ICB in short-term three-dimensional microfluidic culture. Response and resistance to ICB was recapitulated using MDOTS derived from established immunocompetent mouse tumor models. MDOTS profiling demonstrated that TBK1/IKKε inhibition enhanced response to PD-1 blockade, which effectively predicted tumor response in vivo Systematic profiling of secreted cytokines in PDOTS captured key features associated with response and resistance to PD-1 blockade. Thus, MDOTS/PDOTS profiling represents a novel platform to evaluate ICB using established murine models as well as clinically relevant patient specimens.Significance: Resistance to PD-1 blockade remains a challenge for many patients, and biomarkers to guide treatment are lacking. Here, we demonstrate feasibility of ex vivo profiling of PD-1 blockade to interrogate the tumor immune microenvironment, develop therapeutic combinations, and facilitate precision immuno-oncology efforts. Cancer Discov; 8(2); 196-215. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Deng et al., p. 216This article is highlighted in the In This Issue feature, p. 127.

Multiple scattering of 13 and 20 MeV electrons by thin foils: a Monte Carlo study with GEANT, Geant4, and PENELOPE

PURPOSE

In this work, recent results from experiments and simulations (with EGSnrc) performed by Ross et al. [Med. Phys. 35, 4121-4131 (2008)] on electron scattering by foils of different materials and thicknesses are compared to those obtained using several Monte Carlo codes.

METHODS

Three codes have been used: GEANT (version 3.21), Geant4 (version 9.1, patch03), and PENELOPE (version 2006). In the case of PENELOPE, mixed and fully detailed simulations have been carried out.

RESULTS

Transverse dose distributions in air have been obtained in order to compare with measurements. The detailed PENELOPE simulations show excellent agreement with experiment. The calculations performed with GEANT and PENELOPE (mixed) agree with experiment within 3% except for the Be foil. In the case of Geant4, the distributions are 5% narrower compared to the experimental ones, though the agreement is very good for the Be foil. Transverse dose distribution in water obtained with PENELOPE (mixed) is 4% wider than those calculated by Ross et al. using EGSnrc and is 1% narrower than the transverse dose distributions in air, as considered in the experiment.

CONCLUSIONS

All the codes give a reasonable agreement (within 5%) with the experimental results for all the material and thicknesses studied.

On the safety assessment of human exposure in the proximity of cellular communications base-station antennas at 900, 1800 and 2170 MHz

In this work, the procedures for safety assessment in the close proximity of cellular communications base-station antennas at three different frequencies (900, 1800 and 2170 MHz) are analysed. For each operating frequency, we have obtained and compared the distances to the antenna from the exposure places where electromagnetic fields are below reference levels and the distances where the specific absorption rate (SAR) values in an exposed person are below the basic restrictions, according to the European safety guidelines. A high-resolution human body model has been located, in front of each base-station antenna as a worst case, at different distances, to compute whole body averaged SAR and maximum 10 g averaged SAR inside the exposed body. The finite-difference time-domain method has been used for both electromagnetic fields and SAR calculations. This paper shows that, for antenna-body distances in the near zone of the antenna, the fact that averaged field values be below the reference levels could, at certain frequencies, not guarantee guidelines compliance based on basic restrictions.

Comparison of FDTD-calculated specific absorption rate in adults and children when using a mobile phone at 900 and 1800 MHz

In this paper, the specific absorption rate (SAR) in scaled human head models is analysed to study possible differences between SAR in the heads of adults and children and for assessment of compliance with the international safety guidelines, while using a mobile phone. The finite-difference time-domain method (FDTD) has been used for calculating SAR values for models of both children and adults, at 900 and 1800 MHz. Maximum 1 g averaged SAR (SAR1 g) and maximum 10 g averaged SAR (SAR10 g) have been calculated in adults and scaled head models for comparison and assessment of compliance with ANSI/IEEE and European guidelines. Results show that peak SAR1 g and peak SAR10 g all trend downwards with decreasing head size but as head size decreases, the percentage of energy absorbed in the brain increases. So, higher SAR in children's brains can be expected depending on whether the thickness of their skulls and surrounding tissues actually depends on age. The SAR in eyes of different sizes, as a critical organ, has also been studied and very similar distributions for the full size and the scaled models have been obtained. Standard limits can only be exceeded in the unpractical situation where the antenna is located at a very short distance in front of the eye.

Synthesis and amyloid binding properties of rhenium complexes: preliminary progress toward a reagent for SPECT imaging of Alzheimer's disease brain

The definitive diagnosis of Alzheimer's disease (AD) requires the detection of amyloid plaques in postmortem brain. Although the amount of fibrillar amyloid roughly correlates with the severity of symptoms at the time of death, the temporal relationship between amyloid deposition, neuronal loss, and cognitive decline is unclear. To elucidate this relationship, a noninvasive, practical method for the quantitation of brain amyloid deposition is required. We describe herein the initial stages of a strategy to accomplish this goal by single photon computed tomographic imaging. The amyloid-binding dye Congo Red was modified to allow its conjugation to the monoamine-monoamide bis(thiol) ligand. This ligand complexes technetium(V) in its neutral oxo form. A biphenyl-containing building block was conjugated to the protected ligand, and the product was coupled to the relevant aromatic compounds. Rhenium oxo complexes, which are isosteric, but nonradioactive, analogues of the potential imaging agent technetium oxo complexes, were synthesized. These complexes bound to Abeta amyloid fibrils produced in vitro and stained amyloid plaques and vascular amyloid in AD brain sections.