Pancharatnam--Berry phase in space-variant polarization-state manipulations with subwavelength gratings

We report the appearance of a geometrical phase in space-variant polarization-state manipulations. This phase is related to the classic Pancharatnam-Berry phase. We show a method with which to calculate it and experimentally demonstrate its effect, using subwavelength metal stripe space-variant gratings. The experiment is based on a unique grating for converting circularly polarized light at a wavelength of 10.6 mum into an azimuthally polarized beam. Our experimental evidence relies on analysis of far-field images of the resultant polarization.

Permeabilizing Cell Membranes with Electric Fields

The biological impact of exogenous, alternating electric fields (AEFs) and direct-current electric fields has a long history of study, ranging from effects on embryonic development to influences on wound healing. In this article, we focus on the application of electric fields for the treatment of cancers. In particular, we outline the clinical impact of tumor treating fields (TTFields), a form of AEFs, on the treatment of cancers such as glioblastoma and mesothelioma. We provide an overview of the standard mechanism of action of TTFields, namely, the capability for AEFs (e.g., TTFields) to disrupt the formation and segregation of the mitotic spindle in actively dividing cells. Though this standard mechanism explains a large part of TTFields' action, it is by no means complete. The standard theory does not account for exogenously applied AEFs' influence directly upon DNA nor upon their capacity to alter the functionality and permeability of cancer cell membranes. This review summarizes the current literature to provide a more comprehensive understanding of AEFs' actions on cell membranes. It gives an overview of three mechanistic models that may explain the more recent observations into AEFs' effects: the voltage-gated ion channel, bioelectrorheological, and electroporation models. Inconsistencies were noted in both effective frequency range and field strength between TTFields versus all three proposed models. We addressed these discrepancies through theoretical investigations into the inhomogeneities of electric fields on cellular membranes as a function of disease state, external microenvironment, and tissue or cellular organization. Lastly, future experimental strategies to validate these findings are outlined. Clinical benefits are inevitably forthcoming.

Chondrocyte deformation induces mitochondrial distortion and heterogeneous intracellular strain fields

Chondrocyte mechanotransduction is poorly understood but may involve cell deformation and associated distortion of intracellular structures and organelles. This study quantifies the intracellular displacement and strain fields associated with chondrocyte deformation and in particular the distortion of the mitochondria network, which may have a role in mechanotransduction. Isolated articular chondrocytes were compressed in agarose constructs and simultaneously visualised using confocal microscopy. An optimised digital image correlation technique was developed to calculate the local intracellular displacement and strain fields using confocal images of fluorescently labelled mitochondria. The mitochondria formed a dynamic fibrous network or reticulum, which co-localised with microtubules and vimentin intermediate filaments. Cell deformation induced distortion of the mitochondria, which collapsed in the axis of compression with a resulting loss of volume. Compression generated heterogeneous intracellular strain fields indicating mechanical heterogeneity within the cytoplasm. The study provides evidence supporting the potential involvement of mitochondrial deformation in chondrocyte mechanotransduction, possibly involving strain-mediated release of reactive oxygen species. Furthermore the heterogeneous strain fields, which appear to be influenced by intracellular structure and organisation, may generate significant heterogeneity in mechanotransduction behaviour for cells subjected to identical levels of deformation.

Computer-generated space-variant polarization elements with subwavelength metal stripes

A novel method of performing two-dimensional space-variant polarization operations is presented. The method is based on determining the local direction and period of subwavelength metal-stripe gratings by use of vectorial optics to obtain any desired continuous polarization change. We demonstrate our approach with specific computer-generated space-variant polarization elements for laser radiation at 10.6mum. The polarization properties are verified with complete space-variant polarization analysis and measurement.

Spatial Fourier-transform polarimetry using space-variant subwavelength metal-stripe polarizers

A novel method for rapid polarization measurement is suggested. The method is based on a periodic space-variant polarizer that can be realized by use of subwavelength metal-stripe gratings. The Stokes parameters of the incident beam are determined by Fourier analysis of the space-variant intensity transmitted through the grating, thus permitting real-time polarization measurement. We discuss the design and realization of such polarizers and demonstrate our technique with polarization measurements of CO(2)-laser radiation at a wavelength of 10.6mum.

Modelling Tumor Treating Fields for the treatment of lung-based tumors

Tumor Treating Fields (TTFields), low-intensity electric fields in the frequency range of 100-500 kHz, exhibit antimitotic activity in cancer cells. TTFields were approved by the U. S. Food and Drug Administration for the treatment of recurrent glioblastoma in 2011. Preclinical evidence and pilot studies suggest that TTFields could be effective for treating certain types of lung cancer, and that treatment efficacy depends on the electric field intensity. To optimize TTFields delivery to the lungs, it is important to understand how TTFields distribute within the chest. Here we present simulations showing how TTFields are distributed in the thorax and torso, and demonstrate how the electric field distribution within the body can be controlled by personalizing the layout of the arrays used to deliver the field.

Computational simulations establish a novel transducer array placement arrangement that extends delivery of therapeutic TTFields to the infratentorium of patients with brainstem gliomas

Background and Purpose

Tumor treating fields (TTFields) are a non-invasive, efficacious treatment modality currently approved for supratentorial glioblastomas. Despite their ability to improve overall survival in supratentorial tumors, the current placement of arrays is limited to the supratentorial head, precluding its use in infratentorial tumors. Infratentorial malignancies are in need of new therapy modalities given their poor prognoses in both children and adults. The aim of this research is to determine whether rearrangement of TTFields may allow for management of infratentorial tumors.

Materials and methods

Delivery of TTFields using Novocure’s prototype Optune™ device human male head model was simulated based on brain MRIs from patients with brainstem gliomas to develop a novel array layout designed to extend adequate infratentorial coverage.

Results

Array placement on the vertex, bilateral posterolateral occiput, and superior-posterior neck achieved intensities above 1.1 V/cm (average 1.7 V/cm; maximum 2.3 V/cm) in the vertical field direction and above 1 V/cm (average 2 V/cm; maximum 2.8 V/cm) in the horizontal field direction of the infratentorium. The calculated field intensity within the simulated tumors were in the therapeutic range and demonstrated the effective delivery of TTFields to the infratentorial brain.

Conclusions

Our findings suggest that rearrangement of the TTFields standard array with placement of electrodes on the vertex, bilateral posterolateral occiput, and superior-posterior neck allows for adequate electric field distribution in the infratentorium that is within the therapeutic range.

RDNA-10. TTFIELDS TREATMENT PLANNING FOR TARGETING MULTIPLE LESIONS SPREAD THROUGHOUT THE BRAIN

Tumor Treating Fields (TTFields) are approved for the treatment of Glioblastoma Multiforme (GBM) in supratentorium. When treating GBM in the suprtaentorial brain, TTFields are delivered using 2 pairs of transducer arrays positioned in close proximity to the tumor. This results in an increased TTFields dose in the affected tumor region, whilst reducing the dose in other regions, particularly the infratentorium. Brain metastases, occur in 10 to 30 percent of adults with cancer, and can occur throughout the brain, including in infratentorial regions. Therefore, when using TTFields to treat brain metastases, it is desirable to deliver TTFields at therapeutic intensities to the entire brain or to the infratentorium depending on the location of the lesions. We performed computational studies to identify array layouts for delivering TTFields at therapeutic intensities to the infratentorium and to the entire brain. The computer simulations utilized a realistic computerized head model of a 40+ years old human male prepared in-house. TTFields could be delivered effectively to the infratentorium using a layout in which a pair of arrays was placed on the lateral aspects of the neck below the ears, and the second pair on the upper head and lower neck yielded field intensities above 1 V/cm in the infratentorial brain. Other layouts in which one pair of arrays was placed on the right temple and left scapula, and the second pair placed on the left temple and right scapula yielded a uniform intensity distribution within the entire brain. This layout could be useful for treating multiple lesion spread in both the infratentorial and supratentorial regions. This study suggests that careful treatment planning could be used to optimize TTFields treatment targeting multiple lesions spread throughout the brain.

NIMG-20. EVALUATION OF HEAD SEGMENTATION QUALITY FOR TREATMENT PLANNING OF TUMOR TREATING FIELDS IN BRAIN TUMORS

Tumor treating fields (TTFields) is an FDA approved therapy for the treatment of glioblastoma multiform (GBM), malignant pleural mesothelioma (MPM), and currently being investigated for additional tumor types. TTFields are delivered to the tumor through the placement of transducer arrays (TAs) placed on the patient’s shaved scalp. The positions of the TAs are associated with treatment outcomes via simulations of the electric fields. Therefore, we are currently developing a method for recommending optimal placement of TAs. A key step to achieve this goal is to correctly segment the head into tissues of similar electrical properties. Visual inspection of segmentation quality is invaluable but time-consuming. Automatic quality assessment can assist in automatic refinement of the segmentation parameters, suggest flaw points to the user and indicate if the segmented method is of sufficient accuracy for TTFields simulation. As a first step in this direction, we identified a set of features that are relevant to atlas-based segmentation and show that these are significantly correlated (p < 0.05) with a similarity measure between gold-standard and automatically computed segmentations. Furthermore, we incorporated these features in a decision tree regressor to predict the similarity of the gold-standard and computed segmentations of 20 TTFields patients using a leave-one-out approach. The predicted similarity measures were highly correlated with the actual ones (average absolute difference 3% (SD = 3%); r = 0.92, p < 0.001). We conclude that automatic quality estimation of segmentations is feasible by incorporating segmentation-relevant features with statistical and machine learning methods, such as decision tree regressor.

EXTH-37. A NOVEL TRANSDUCER ARRAY LAYOUT FOR DELIVERING TUMOR TREATING FIELDS TO THE SPINE

Tumor Treating Fields (TTFields) are an antimitotic technology utilising electric fields to disrupt mitosis in cancer cells. TTFields are currently approved by the FDA for the treatment of Glioblastoma Multiforme (GBM) and Malignant Pleural Mesothelioma (MPM). TTFields are delivered through 2 pairs of transducer arrays placed on the patient’s skin. Each pair delivers TTFields in a single direction, and the pairs are placed to provide perpendicular field. Preclinical studies show that 1V/cm is the clinical threshold for the treatment to be effective. Some types of cancers send metastases to the spinal cord and CSF, i.e. leptomeningeal disease. The purpose of this study was to find transducer array layouts that deliver TTFields to the spine at therapeutic intensities of above 1 V/cm. Computational simulations testing the delivery of TTFields to the spine were performed using the Sim4Life 4.0 (ZMT Zurich) computational platform, and the Duke 3.1 and Ella 3.0 (ITI’S, Zurich) realistic computational models of a male and female respectively. “Standard” layouts in which a pair of arrays are placed on the front and back of the patient and second pair on the lateral aspects of the patient failed to deliver TTFields at therapeutic intensities to the spinal cord. This is probably because the spinal cord is surrounded by the CSF and spine, which shunt the electric fields from reaching the spinal cord. However, field intensities above 1 V/cm were observed when delivering TTFields when both arrays were placed on the patients back, with a first array placed close to the neck, and second array placed towards the thighs. In this case, the spinal cord and surrounding CSF act as a conductive cable, directing the electric field along the spine. This novel layout opens the possibility for treating cancerous disease along the spine.

CSIG-26. IS INTRINSIC APOPTOSIS THE SIGNALING PATHWAY ACTIVATED BY TUMOR-TREATING FIELDS FOR GLIOBLASTOMA?

Increasingly, tumor-treating fields (TTFields, 2 V/cm, 200 kHz) are accepted as the fourth treatment modality for glioblastoma. Evidence shows that substituting non-steroidal inflammation control (celecoxib) for dexamethasone increases overall survival from 4.8 to 11.0 months, and more recently, up to 60 months. Toward explaining TTFields mechanism of action (MoA), our numerical simulations indicate that TTFields disrupt functionality of microtubules, which in turn trigger the intrinsic apoptotic pathway independent of cell cycle checkpoints. We present the theory and empirical evidence. 1) TTFields act similarly to chemotherapeutic ‘spindle poisons’ by interfering with microtubule (MT) polymerization, increasing free tubulin by 20% in relative terms; 2) Finite element modeling shows TTFields amplify electric field strength, in accord with empirical results, a) along the MT when aligned with the cell axis, where field strength exceeds 10–16 N required to disrupt motor protein transit, and b) 15x at MT ends when orthogonal to cell axis; 3) Either through producing excess free tubulin, which may block voltage-dependent anion channels, or direct effects on the mitochondrial inner and outer membranes, TTFields inhibit expression of pro-survival protein Bcl-2; 4) Decreased Bcl-2 expression activates the intrinsic apoptotic pathway in a novel cell-cycle-checkpoint and caspase-independent manner; 5) Patients using low (< 4.1 mg/day) vs. high (>4.1 mg/day) dexamethasone doses experienced an average 8.7 vs. 3.2 months OS and up to 60 months; 6) Numerous studies in both brain and other tissues show that dexamethasone a) promotes extrinsic, immune-system apoptosis and b) inhibits intrinsic, Bcl-2/Bax mediated apoptosis; 7) Downstream effects of intrinsic apoptosis are remarkably similar to empirically-observed effects of TTFields on tumor cells. Research supported by Novocure Ltd. Dept of Neurosurgery, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston MA USA. carlsokw@bidmc.harvard.edu. Dept of Physics, University of Alberta, Edmonton, Canada, Novocure Ltd., Haifa, Israel.