Enhanced cavitation activity in a slab-shaped optical absorber during photo-mediated ultrasound therapy.
Abstract Recently, new studies have shown that combined laser and ultrasound, or photo-mediated ultrasound therapy (PUT), can enhance cavitation in optically absorptive targets to disrupt tissues through photoacoustic (PA) effect. These studies, including both experimental and theoretical investigations, have largely focused on blood vessels, which are modeled as cylindrically-shaped optical absorbers for PA wave generation and propagation. However, in many clinical situations, target tissues may not be cylindrically-shaped. In this paper we investigated the effect of PUT on a slab-shaped optical absorber, much la...
Source: Physics in Medicine and Biology - November 12, 2019 Category: Physics Authors: Hazlewood D, Yang X Tags: Phys Med Biol Source Type: research

gPET: A GPU-based, accurate and efficient Monte Carlo simulation tool for PET.
Abstract Monte Carlo (MC) simulation method plays an essential role in the refinement and development of positron emission tomography (PET) systems. However, most existing MC simulation packages suffer from long execution time for practical PET simulations. To fully address this issue, we developed and validated gPET, a graphics processing unit (GPU)-based MC simulation tool for PET. gPET was built on the NVidia CUDA platform. The simulation process was modularized into three functional parts and carried out by the GPU parallel threads: 1) source management, including positron decay, transport and annihilation; 2)...
Source: Physics in Medicine and Biology - November 11, 2019 Category: Physics Authors: Lai Y, Zhong Y, Chalise AR, Shao Y, Jin M, Jia X, Chi Y Tags: Phys Med Biol Source Type: research

Towards 4D dedicated breast CT perfusion imaging of cancer: development and validation of computer simulated images.
In conclusion, the proposed pipeline could simulate images with a good level of realism, resulting in a tool that can be used for the design, development, and optimization of a 4D dedicated breast CT system. PMID: 31703216 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - November 8, 2019 Category: Physics Authors: Caballo M, Michielsen K, Fedon C, Sechopoulos I Tags: Phys Med Biol Source Type: research

Radiation dose efficiency of multi-energy CT for dual-contrast imaging.
Abstract Compared to traditional multi-scan single-energy CT (SECT), one potential advantage of single-scan multi-energy CT (MECT) proposed for simultaneous imaging of multiple contrast agents is the radiation dose reduction. This phantom study aims to rigorously evaluate whether the radiation dose can truly be reduced in a single-scan MECT protocol (MECT_1s) in biphasic liver imaging with iodine and gadolinium, and small bowel imaging with iodine and bismuth, compared to traditional two-scan SECT protocols (SECT_2s). For MECT_1s, mixed iodine/gadolinium samples were prepared corresponding to late arterial/portal-...
Source: Physics in Medicine and Biology - November 8, 2019 Category: Physics Authors: Ren L, Rajendran K, McCollough CH, Yu L Tags: Phys Med Biol Source Type: research

Multi-objective ensemble deep learning using electronic health records to predict outcomes after lung cancer radiotherapy.
Abstract Accurately predicting treatment outcome is crucial for creating personalized treatment plans and follow-up schedules. Electronic health records (EHRs) contain valuable patient-specific information that can be leveraged to improve outcome prediction. We propose a reliable multi-objective ensemble deep learning (MoEDL) method that uses features extracted from EHRs to predict high risk of treatment failure after radiotherapy in patients with lung cancer. The dataset used in this study contains EHRs of 814 patients who had not achieved disease-free status and 193 patients who were disease-free with at least o...
Source: Physics in Medicine and Biology - November 7, 2019 Category: Physics Authors: Wang R, Weng Y, Zhou Z, Chen L, Hao H, Wang J Tags: Phys Med Biol Source Type: research

A collection input based support tensor machine for lesion malignancy classification in digital breast tomosynthesis.
Abstract Digital breast tomosynthesis (DBT) with improved lesion conspicuity and characterization has been adopted in screening practice. DBT-based diagnosis strongly depends on physicians' experience, so an automatic lesion malignancy classification model using DBT could improve the consistency of diagnosis among different physicians. Tensor-based approaches that use the original imaging data as input have shown promising results for many classification tasks. However, DBT data are pseudo-3D volumetric imaging as the slice spacing of DBT is much coarser than that of the in-plane resolution. Thus, directly constru...
Source: Physics in Medicine and Biology - November 7, 2019 Category: Physics Authors: Yang B, Wu Y, Zhou Z, Li S, Qin G, Chen L, Wang J Tags: Phys Med Biol Source Type: research

Soft-tissue prostate intrafraction motion tracking in 3D cine-MR for MR-guided radiotherapy.
CONCLUSION: A fast, robust and accurate soft tissue tracking algorithm was developed which obviates the need for fiducial markers during MR-guided prostate radiotherapy. To our knowledge, this is the first data using full 3D cine-MR images for real-time soft-tissue prostate tracking, which is validated against previously obtained marker tracking data. PMID: 31698351 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - November 7, 2019 Category: Physics Authors: de Muinck Keizer DM, Kerkmeijer LGW, Maspero M, Andreychenko A, van der Voort van Zyp JRN, Van den Berg CAT, Raaymakers BW, Lagendijk JJW, de Boer JCJ Tags: Phys Med Biol Source Type: research

MR-MOTUS: model-based non-rigid motion estimation for MR-guided radiotherapy using a reference image and minimal k-space data.
Abstract Time-resolved motion estimation from MRI data has received an increasing amount of interest due to the advent of the MR-Linac. The combination of an MRI scanner and a linear accelerator enables radiation plan adaptation based on internal organ motion estimated from MRI data. However, time-resolved estimation of this motion from MRI data still remains a challenge. In light of this application, we propose MR-MOTUS, a framework to estimate non-rigid 3D motion from minimalk-space data. MR-MOTUS consists of two main components: (1) a signal model that explicitly relates thek-space signal of a deforming object ...
Source: Physics in Medicine and Biology - November 7, 2019 Category: Physics Authors: Huttinga NRF, Van den Berg CAT, Luijten PR, Sbrizzi A Tags: Phys Med Biol Source Type: research

Increasing the precision in the estimates of noise power spectrum in digital x-ray imaging systems.
Abstract The noise power spectrum (NPS) of a digital x-ray imaging device is usually estimated from the average of periodograms of ROIs in images obtained with uniform radiation fields. The purpose of this work was developing a new estimator for calculating the NPS and comparing its uncertainties with those of the smoothed periodogram. The new estimator is built by removing those addends in the summation of the periodogram that do not contain information on stochastic noise. This was carried out by applying a short-length lag window to the autocorrelation function of noise. The length of the window was obtained fr...
Source: Physics in Medicine and Biology - November 6, 2019 Category: Physics Authors: Gonzalez-Lopez A Tags: Phys Med Biol Source Type: research

Technical advances in X-ray microbeam radiation therapy.
This article reviews technical developments in MRT and discusses existing solutions for dosimetric validation, reliable treatment planning and safety. Instrumentation at synchrotron facilities, including beam production, collimators and patient positioning systems, is also discussed. Specific solutions reviewed in this article include: dosimetry techniques that can cope with high spatial resolution, low photon energies and extremely high dose rates of up to \SI{15000}{Gy/s}, dose calculation algorithms - apart from pure Monte Carlo Simulations - to overcome the challenge of small voxel sizes and a wide dynamic dose-range, ...
Source: Physics in Medicine and Biology - November 6, 2019 Category: Physics Authors: Bartzsch SH, Corde S, Crosbie JC, Day LRJ, Donzelli M, Krisch M, Lerch MLF, Pellicioli P, Smyth LML, Tehei M Tags: Phys Med Biol Source Type: research

Automatic classification of dental artifact status for efficient image veracity checks: effects of image resolution and convolutional neural network depth.
CONCLUSION: Our experiments demonstrate the potential to automate specific quality assurance tasks required for unbiased and robust automated pipeline and image analysis research. Additionally, we determined that there is an opportunity to simplify CNNs with smaller resampling grids to make the process more amenable to very large datasets that will be available in the future. PMID: 31683260 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - November 4, 2019 Category: Physics Authors: Welch ML, McIntosh C, Purdie TG, Wee L, Traverso A, Dekker A, Haibe-Kains B, Jaffray DA Tags: Phys Med Biol Source Type: research

Dose-volume histogram prediction in volumetric modulated arc therapy for nasopharyngeal carcinomas based on uniform-intensity radiation with equal angle intervals.
In this study, we developed a gated recurrent unit (GRU)-based recurrent neural network (RNN) for dose-volume histogram (DVH) prediction in volumetric modulated arc therapy (VMAT) planning for nasopharyngeal carcinomas (NPCs) based on uniform-intensity radiation with equal angle intervals and investigated the feasibility and usefulness of this method in optimization. METHODS AND MATERIALS: 124 NPC patients were selected from a database containing clinical VMAT plans from 2015 to 2018; of these patients, 100 were used for training the GRU-RNN, and 24 were used for testing. Regarding the prescribed doses covered 95 % of...
Source: Physics in Medicine and Biology - November 4, 2019 Category: Physics Authors: Zhuang Y, Han J, Chen L, Liu X Tags: Phys Med Biol Source Type: research

< i > In silico < /i > evaluation of the thermal stress induced by MRI switched gradient fields in patients with metallic hip implant.
In silico evaluation of the thermal stress induced by MRI switched gradient fields in patients with metallic hip implant. Phys Med Biol. 2019 Nov 04;: Authors: Arduino A, Bottauscio O, Brühl R, Chiampi M, Zilberti L Abstract This work focuses on the in silico evaluation of the energy deposed by MRI switched gradient fields in bulk metallic implants and the consequent temperature increase in the surrounding tissues. An original computational strategy, based on the subdivision of the gradient coil switching sequences into sub-signals and on the time-harmonic electromagnetic field solution, allows t...
Source: Physics in Medicine and Biology - November 4, 2019 Category: Physics Authors: Arduino A, Bottauscio O, Brühl R, Chiampi M, Zilberti L Tags: Phys Med Biol Source Type: research

Temperature control in TTFields therapy of GBM: impact on the duty cycle and tissue temperature.
Abstract In TTFields therapy, Optune® is used to deliver the electric field to the tumor via 4 transducer arrays. This device monitors the temperature of the transducers and reduces the current whenever a transducer reaches 41ºC. Our aim is to quantify Optune's duty cycle and to predict the steady-state temperature distribution in the head during GBM treatment. We used a realistic head model and the finite element method to solve Pennes equation and to simulate how Optune operates considering that current reduces to zero when the thermal limit is reached. The thermal impact was evaluated considering the m...
Source: Physics in Medicine and Biology - October 31, 2019 Category: Physics Authors: Gentilal N, Salvador R, Miranda PC Tags: Phys Med Biol Source Type: research

Accounting for respiratory motion in small serial structures during radiotherapy planning: proof of concept in virtual bronchoscopy-guided lung functional avoidance radiotherapy.
Abstract Respiratory motion management techniques in radiotherapy (RT) planning are primarily focused on maintaining tumor target coverage. An inadequately addressed need is accounting for motion in dosimetric estimations in smaller serial structures. Accurate dose estimations in such structures are more sensitive to motion because respiration can cause them to move completely in or out of a high dose-gradient field. In this work, we study three motion management strategies (m1-m3) to find an accurate method to estimate the dosimetry in airways. To validate these methods, we generated a "ground truth" di...
Source: Physics in Medicine and Biology - October 30, 2019 Category: Physics Authors: Vicente E, Modiri A, Yu KC, Wibowo H, Yan Y, Timmerman RD, Sawant A Tags: Phys Med Biol Source Type: research

Dosimetric performance of the Elekta Unity MR-linac system: 2D and 3D dosimetry in anthropomorphic inhomogeneous geometry.
Abstract Following the clinical introduction of the Elekta Unity MR-linac, there is an urgent need for development of dosimetry protocols and tools, not affected by the presence of magnetic field. This work presents a benchmarking methodology comprising 2D/3D passive dosimetry and involving on-couch adaptive treatment planning, a unique step in MR-linac workflows. Two identical commercially available 3D-printed head phantoms (featuring realistic bone anatomy and MR/CT contrast) were employed. One phantom incorporated a film dosimetry insert, while the second was filled with polymer gel. Gel dose-response character...
Source: Physics in Medicine and Biology - October 30, 2019 Category: Physics Authors: Pappas E, Kalaitzakis G, Boursianis T, Zoros E, Zourari K, Pappas EP, Makris DN, Seimenis I, Efstathopoulos EP, Maris TG Tags: Phys Med Biol Source Type: research

Physical characteristics at the turnover-points of relative biological effect (RBE) with linear energy transfer (LET).
CONCLUSIONS: Each ion probably has a unique LETU value. Kinematic studies show maximum bio-effectiveness occurs at particle velocities where electron stripping remains at around 99% and where the velocity per nucleon is around 3-4 nm.fs-1. PMID: 31665711 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 30, 2019 Category: Physics Authors: Jones B, Hill MA Tags: Phys Med Biol Source Type: research

Computational analysis of non-invasive deep brain stimulation based on interfering electric fields.
The objective of this study is to provide insight into the fundamental mechanisms of this strategy and assess the potential uses of this method through computational analysis. Approach‎. ‎Analytical and numerical methods are used to compute the electric potential and field distributions generated during NDBS in homogeneous and inhomogeneous models of the brain‎. ‎The computational results are used for specifying the activated area in the brain (macroscopic approach)‎, ‎and quantifying its relationships to the stimulation parameters‎. ‎Two automatic algorithms‎, ‎using artificial neur...
Source: Physics in Medicine and Biology - October 29, 2019 Category: Physics Authors: Karimi F, Attarpour A, Amirfattahi R, Zeidaabadi Nezhad A Tags: Phys Med Biol Source Type: research

The production of positron emitters with millisecond half-life during helium beam radiotherapy.
This study presents the first measurements of the production of short-lived positron emitters in water, graphite, calcium and phosphorus targets irradiated with 59 MeV/u 3He and 50 MeV/u 4He beams. For these targets, the most produced short-lived nuclides are 13O/12N (T1/2 = 8.6/11 ms) on water, 13O/12N on graphite, 43Ti/41Sc/42Sc (T1/2 = 509 - 680 ms) on calcium, 28P (T1/2 = 268 ms) on phosphorus. A translation of the results from elemental targets to PMMA and representative tissues such as adipose tissue, muscle, compact and cortical bone, shows the dominance of 13O/12N in at least the first 20 s of an irradiation with 4...
Source: Physics in Medicine and Biology - October 28, 2019 Category: Physics Authors: Ozoemelam IS, van der Graaf ER, Brandenburg S, Dendooven P Tags: Phys Med Biol Source Type: research

Block matching frame based material reconstruction for spectral CT.
Abstract Spectral computed tomography (CT) has a great potential in material identification and decomposition. To achieve high-quality material composition images and further suppress the x-ray beam hardening artifacts, we first propose a one-step material reconstruction model based on Taylor's first-order expansion. Then, we develop a basic material reconstruction method named material simultaneous algebraic reconstruction technique (MSART). Considering the local similarity of each material image, we incorporate a powerful block matching frame (BMF) into the material reconstruction (MR) model and generate a BMF b...
Source: Physics in Medicine and Biology - October 28, 2019 Category: Physics Authors: Wu W, Wang Q, Liu F, Zhu Y, Yu H Tags: Phys Med Biol Source Type: research

Characterization of an x-ray source with a partitioned diamond-tungsten target for electronic brachytherapy with 3D beam directionality.
This article reports the spectral and dosimetric characterization of the SculpturaTMx-ray source through a combination of measurements and Monte Carlo simulations for operating points between 50 - 100 kV. Excellent agreement (~5% discrepancy) between the simulations and measurements was obtained for in-air dose rate characterization. The validated simulations were then used to calculate the dose distribution in water. Dose rates of>2 cGy/min/µA can be produced at 100 kV, thus delivering 10 Gy in 1 minute for typical operating conditions. The dose distributions are sharply peaked, with a full-width at half-maximum ...
Source: Physics in Medicine and Biology - October 25, 2019 Category: Physics Authors: Badali DS, Plateau GR, Ellenor CW, Ku CY, Vatahov P, Esterline J, Wilfley BP, Mitchell CR, Fishman K, Funk T Tags: Phys Med Biol Source Type: research

Dynamic lung phantom commissioning for 4D dose assessment in proton therapy.
Abstract Anthropomorphic phantoms mimicking organ and tumor motion of patients are essential for end-to-end testing of motion mitigation techniques in ion beam therapy. In this work a commissioning procedure developed with the in-house designed respiratory phantom ARDOS (Advanced Radiation DOSimetry system) is presented. The phantom was tested and benchmarked for 4-dimensional dose verification in proton therapy, which included: characterization of the tissue equivalent materials from computed tomography (CT) imaging, assessment of dose calculation accuracy in critical structures of the phantom, and testing variou...
Source: Physics in Medicine and Biology - October 25, 2019 Category: Physics Authors: Kostiukhina N, Palmans H, Stock M, Georg D, Knaeusl B Tags: Phys Med Biol Source Type: research

Prediction of dose-volume histograms in nasopharyngeal cancer IMRT using geometric and dosimetric information.
Abstract PURPOSE: A method using both patient geometric and dosimetric information was proposed to predict dose-volume histograms (DVHs) of organs at risk (OARs) for a nasopharyngeal cancer (NPC) intensity-modulated radiation therapy (IMRT) plan. METHODS AND MATERIALS: A total of 106 nine-field IMRT NPC plans were used in this study. Twenty-six plans were randomly selected as testing cases, and the remaining plans were used as the training data. A method employing geometric and dosimetric information was developed for OAR DVH prediction. The dosimetric information was derived from an initial dose calculation ...
Source: Physics in Medicine and Biology - October 24, 2019 Category: Physics Authors: Jiao SX, Chen L, Zhu J, Wang M, Liu X Tags: Phys Med Biol Source Type: research

A systematic evaluation and optimization of automatic detection of ulcers in wireless capsule endoscopy on a large dataset using deep convolutional neural networks.
Abstract Compared with conventional gastroscopy which is invasive and painful, wireless capsule endoscopy (WCE) can provide noninvasive examination of gastrointestinal (GI) tract. The WCE video can effectively support physicians to reach a diagnostic decision while a huge number of images need to be analyzed (more than 50,000 frames per patient). In this paper, we propose a computer-aided diagnosis method called second glance (secG) detection framework for automatic detection of ulcers based on deep convolutional neural networks that provides both classification confidence and bounding box of lesion area. We evalu...
Source: Physics in Medicine and Biology - October 23, 2019 Category: Physics Authors: Wang S, Xing Y, Zhang L, Gao H, Zhang H Tags: Phys Med Biol Source Type: research

Computer-aided diagnosis system for breast ultrasound images using deep learning.
Abstract The purpose of this study was to develop a computer-aided diagnosis (CAD) system for the classification of malignant and benign masses in the breast using ultrasonography based on a convolutional neural network (CNN), a state-of-the-art deep learning technique. We explored the regions for the correct classification by generating a heat map that presented the important regions used by the CNN for human malignancy/benign classification. Clinical data was obtained from a large-scale clinical trial previously conducted by the Japan Association of Breast and Thyroid Sonology. Images of 1536 breast masses (897 ...
Source: Physics in Medicine and Biology - October 23, 2019 Category: Physics Authors: Tanaka H, Chiu SW, Watanabe T, Kaoku S, Yamaguchi T Tags: Phys Med Biol Source Type: research

Removal of computed tomography ring artifacts via radial basis function artificial neural networks.
In this study, a radial basis function neural network (RBFNN) was used to remove ring artifacts. The proposed method employs polar coordinate transformation. First, ring artifacts were transformed into linear artifacts by polar coordinate transformation. Then, smoothing operators were applied to locate these artifacts exactly. Subsequently, RBFNN was operated on each linear artifact. The neuron numbers of the input, hidden, and output layers of the neural network were 8, 40, and 1, respectively. Neurons in the input layer were selected according to the characteristics of the artifact itself and its relationship with the su...
Source: Physics in Medicine and Biology - October 22, 2019 Category: Physics Authors: Chao Z, Kim HJ Tags: Phys Med Biol Source Type: research

Modeling tissue-selective cavitation damage.
In this study, numerical simulations are used to calculate stress, strain, and strain rate fields produced by bubble oscillation under histotripsy forcing in a variety of tissues with literature-sourced viscoelastic and acoustic properties. Strain field calculations are then used to predict a theoretical damage radius using tissue ultimate strain data. Simulation results support the hypothesis that differential tissue responses could be used to design tissue--selective treatments. Results agree with studies correlating tissue ultimate fractional strain with resistance to histotripsy ablation and are also consistent with ex...
Source: Physics in Medicine and Biology - October 22, 2019 Category: Physics Authors: Mancia L, Vlaisavljevich E, Yousefi N, Rodriguez M, Ziemlewicz TJ, Lee FT, Henann D, Franck C, Xu Z, Johnsen E Tags: Phys Med Biol Source Type: research

Biomechanical quality assurance criteria for deformable image registration algorithms used in radiotherapy guidance.
Abstract Image-guided radiation therapy (IGRT) allows radiation dose deposition with a high degree of geometric accuracy. Previous studies have demonstrated that such therapies may benefit from the employment of deformable image registration (DIR) algorithms, which allow both the automatic tracking of anatomical changes and accumulation of the delivered radiation dose over time. In order to ensure patient care and safety, however, the estimated deformations must be subjected to stringent quality assurance (QA) measures. In the present study we propose to extend the state-of-the-art methodology for QA of DIR algori...
Source: Physics in Medicine and Biology - October 22, 2019 Category: Physics Authors: Zachiu C, Denis de Senneville B, Raaymakers BW, Ries MG Tags: Phys Med Biol Source Type: research

Patient and scanner-specific variable acquisition times for whole-body PET/CT imaging.
raj R Abstract Image quality in positron emission tomography (PET) is limited by the number of detected photons. Heavier patients present higher photon attenuation levels, thus increasing image noise. In this work, we propose a new method that uses the combined patient attenuation/system matrix together with a tracer uptake prediction model to optimize scan times for different bed positions in whole body scans. Our main goal is to achieve consistent noise levels across patients and anatomical regions. We propose to optimize scan times for individual bed positions, for patients of any size, based on the scanner sen...
Source: Physics in Medicine and Biology - October 21, 2019 Category: Physics Authors: Namías M, Jeraj R Tags: Phys Med Biol Source Type: research

Time-of-flight (TOF) implementation for PET reconstruction in practice.
Abstract The time-of-flight (TOF) feature of PET scanners has been used for a long time in PET reconstruction, but many implementational aspects are still incomplete or ambiguous in the literature. Here we formalize and present theoretical and practical implementation details for the reconstruction of clinical TOF histogram and list-mode data using ML-EM. Relevant aspects include the computation of the TOF component of the system matrix, the processing of TOF bins, the use of estimations of random and scattered coincidences, and differences between histogram and list-mode ML-EM TOF reconstruction. Several approach...
Source: Physics in Medicine and Biology - October 18, 2019 Category: Physics Authors: Filipovic M, Comtat C, Stute S Tags: Phys Med Biol Source Type: research

Absorbed dose calorimetry.
This article reviews the development and summarizes the state-of-the-art in absorbed dose calorimetry for all the common clinical beam modalities covered in reference dosimetry codes of practice, as well as for small and nonstandard fields, and brachytherapy. It focuses primarily on work performed in the last ten years by national laboratories and research institutions and is not restricted to primary standard instruments. The most recent absorbed dose calorimetry review article was published over twenty years ago by Ross and Klassen (1996), and even then, its scope was limited to water calorimeters. Since the application ...
Source: Physics in Medicine and Biology - October 18, 2019 Category: Physics Authors: Renaud J, Palmans H, Sarfehnia A, Seuntjens J Tags: Phys Med Biol Source Type: research

Cell Migration in Microfluidic Devices: Invadosomes Formation in Confined Environments.
Abstract The last 20 years have seen the blooming of microfluidics technologies applied to biological sciences. Microfluidics provides effective tools for biological analysis, allowing the experimentalists to extend their playground to single cells and single molecules, with high throughput and resolution which were inconceivable few decades ago. In particular, microfluidic devices are profoundly changing the conventional way of studying the cell motility and cell migratory dynamics. In this chapter we will furnish a comprehensive view of the advancements made in the research domain of confinement-induced cel...
Source: Physics in Medicine and Biology - October 17, 2019 Category: Physics Authors: Chi PY, Spuul P, Tseng FG, Genot E, Chou CF, Taloni A Tags: Adv Exp Med Biol Source Type: research

CBCT correction using a cycle-consistent generative adversarial network and unpaired training to enable photon and proton dose calculation.
Abstract In presence of inter-fractional anatomical changes, clinical benefits are anticipated from image-guided adaptive radiotherapy. Nowadays, cone-beam CT (CBCT) imaging is mostly utilized during pre-treatment imaging for position verification. Due to various artifacts, image quality is typically not sufficient for photon or proton dose calculation, thus demanding accurate CBCT correction, as potentially provided by deep learning techniques. This work aimed at investigating the feasibility of utilizing a cycle-consistent generative adversarial network (cycleGAN) for prostate CBCT correction using unpaired trai...
Source: Physics in Medicine and Biology - October 14, 2019 Category: Physics Authors: Kurz C, Maspero M, Savenije MHF, Landry G, Kamp F, Pinto M, Li M, Parodi K, Belka C, Van den Berg CAT Tags: Phys Med Biol Source Type: research

End-to-end test of an online adaptive treatment procedure in MR-guided radiotherapy using a phantom with anthropomorphic structures.
CP Abstract Online adaptive treatment procedures in magnetic resonance (MR)-guided radiotherapy (MRgRT) allow compensating for inter-fractional anatomical variations in the patient. Clinical implementation of these procedures, however, requires specific end-to-end tests to validate the treatment chain including imaging, treatment planning, positioning, treatment plan adaption and accurate dose delivery. For this purpose, a new phantom with reproducibly adjustable anthropomorphic structures has been developed. These structures can be filled either with contrast materials providing anthropomorphic image contrast in...
Source: Physics in Medicine and Biology - October 14, 2019 Category: Physics Authors: Elter A, Dorsch S, Mann P, Runz A, Johnen W, Spindeldreier CK, Klüter S, Karger CP Tags: Phys Med Biol Source Type: research

A mathematical optimization model for spatial adjustments of dose distributions in high dose-rate brachytherapy.
The objective function considers pairs of dose points and each pair is given a distance-based penalty if the dose is either too high or too low at both dose points. Constraints are included to retain dosimetric indices at acceptable levels. Our model is designed to automate the manual adjustment step in the planning process. In the automatic adjustment step large-scale optimization models are solved. We show reductions of the volumes of the largest hot and cold spots, and the computing times are feasible in clinical practice. PMID: 31610533 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 14, 2019 Category: Physics Authors: Morén B, Larsson T, Carlsson Tedgren Å Tags: Phys Med Biol Source Type: research

Development and validation of single field multi-ion particle therapy treatments.
i A Abstract PURPOSE: To develop and validate combined ion-beam with constant RBE (CICR) particle therapy in single field arrangements for improved treatment efficacy, robustness and normal tissue sparing. METHODS: The PRECISE (PaRticle thErapy using single and Combined Ion optimization StratEgies) treatment planning system (TPS) was developed to investigate clinical viability of CICR treatments. Single-field uniform dose (SFUD) with a single ion (p, He, or C) and CICR (C-p and C-He) treatments were generated for three patient cases with a clinically prescribed dose of 3 Gy(RBE) per fraction. Spread-out Bragg...
Source: Physics in Medicine and Biology - October 11, 2019 Category: Physics Authors: Kopp B, Mein S, Dokic I, Harrabi S, Böhlen TT, Haberer T, Debus J, Abdollahi A, Mairani A Tags: Int J Radiat Oncol Biol Phys Source Type: research

Coupled thermo-electro-mechanical models for thermal ablation of biological tissues and heat relaxation time effects.
Abstract Thermal ablation is a widely applied electrosurgical process in medical treatment of soft biological tissues. Numerical modeling and simulations play an important role in prediction of temperature distribution and damage volume during the treatment planning stage of associated therapies. In this contribution we report a coupled thermo-electro-mechanical model, accounting for heat relaxation time, for more accurate and precise prediction of the temperature distribution, tissue deformation and damage volume during the thermal ablation of biological tissues. Finite element solutions are obtained for most wid...
Source: Physics in Medicine and Biology - October 10, 2019 Category: Physics Authors: Singh S, Melnik RVN Tags: Phys Med Biol Source Type: research

Reconstructing 3-D proton dose distribution using ionoacoustics.
In conclusion, this numerical study suggests that the ionoacoustic wave field may well be used to monitor the proton dose distribution during breast cancer treatment. PMID: 31600743 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 10, 2019 Category: Physics Authors: van Dongen KWA, de Blecourt AJ, Lens E, Schaart DR, Vos FM Tags: Phys Med Biol Source Type: research

A method to reconstruct intra-fractional liver motion in rotational radiotherapy using linear fiducial markers.
In this study, we developed a Six Degree of Freedom Projection Marker Matching method (6-DoF PM3) to reconstruct translational and rotational liver tumor motion in a rotational treatment delivery, such as volumetric modulated arc therapy (VMAT). Specifically, we modeled the use of two gold markers implanted in a linear form. The four endpoints of the two gold linear markers were used as tracking surrogates. During delivery, kV x-ray projection images were acquired. A method was developed to automatically identify the 2D marker-endpoints on the projection images. To determine marker positions in 3D, we formulated an optimiz...
Source: Physics in Medicine and Biology - October 8, 2019 Category: Physics Authors: Chi Y, Shen C, Li B, Zhang Y, Yang M, Folkert MR, Jia X Tags: Phys Med Biol Source Type: research

The importance of dead material within a tumour on the dynamics in response to radiotherapy.
We present a three phase tumour growth model that accounts for the effects of radiotherapy and use it to investigate how dead material within the tumour may affect the spatio-temporal tumour response dynamics. We use numerical simulation of the model equations to characterise qualitatively different tumour volume dynamics in response to fractionated radiotherapy. We demonstrate examples, and associated parameter values, for which the properties of the dead material significantly alter the observed tumour volume dynamics throughout treatment. These simulations suggest that for some cases it may not be possible to accurately...
Source: Physics in Medicine and Biology - October 8, 2019 Category: Physics Authors: Lewin T, Byrne H, Maini PK, Caudell JJ, Moros EG, Enderling H Tags: Phys Med Biol Source Type: research

Reducing crosstalk in optically-pumped magnetometer arrays.
Abstract Optically pumped magnetometers (OPMs) operating in the spin-exchange relaxation-free regime are emerging as alternative sensors to superconducting quantum interference devices (SQUIDs) for magnetoencephalography (MEG). As the number of OPMs in a single imaging system increases to rival SQUID MEG systems, cross-talk between nearby sensors limits the measurement accuracy. We experimentally demonstrate a coil geometry, which generates an order of magnitude less cross-talk (less than 0.5 %) than a Helmholtz coil (8 %). The new coil design is simple and compact, requiring two coaxial coil pairs that add 1 mm t...
Source: Physics in Medicine and Biology - October 8, 2019 Category: Physics Authors: Nardelli N, Krzyzewski SP, Knappe S Tags: Phys Med Biol Source Type: research

Effect of grid geometry on the transmission properties of 2D grids for flat detectors in CBCT.
This study also implies that 2D grids can provide substantially better scatter suppression and primary transmission than high-performance 1D grids currently available. PMID: 31585444 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 4, 2019 Category: Physics Authors: Altunbas C, Alexeev T, Miften M, Kavanagh B Tags: Phys Med Biol Source Type: research

A comparison between unfocused and focused transmit strategies in cardiac strain imaging.
Abstract Unfocused ultrasound imaging, particularly coherent compounding with diverging waves, is a commonly employed high-frame rate transmit strategy in cardiac strain imaging. However, the accuracy and precision of diverging wave imaging compared to focused-beam transmit approaches in human subjects is unknown. Three transmit strategies-coherent compounding imaging, composite focused imaging with ECG gating and narrow-beams, and focused imaging with wide-beams-were compared in simulation and in transthoracic imaging of healthy human subjects (n=7). The focused narrow-beam sequence estimated radial end-systolic ...
Source: Physics in Medicine and Biology - October 4, 2019 Category: Physics Authors: Sayseng V, Grondin J, Weber RA, Konofagou EE Tags: Phys Med Biol Source Type: research

Quality assurance for gamma knife perfexion using the exradin W1 plastic scintillation detector and Lucy phantom.
CONCLUSIONS: In light of our results, the Exradin W1 PSD is well suited for beam quality assurance of a Gamma Knife Perfexion irradiator. PMID: 31581139 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - October 3, 2019 Category: Physics Authors: Therriault-Proulx F, Pino R, Yang JN, Beddar S Tags: Phys Med Biol Source Type: research

Partial-ring PET image restoration using a deep learning based method.
In this study, we investigated the performance of a deep learning (DL) based method for the recovery of partial-ring PET images. Twenty digital brain phantoms were used in the Monte Carlo simulation toolkit, SimSET, to simulate 15-minute full-ring PET scans. Partial-ring PET data were generated from full-ring PET data by removing coincidence events that hit these specific detector blocks. A convolutional neural network based on the residual U-Net architecture was trained to predict full-ring data from partial-ring data in either the projection or image domain. The performance of the proposed DL-based method was evaluated b...
Source: Physics in Medicine and Biology - October 3, 2019 Category: Physics Authors: Liu CC, Huang HM Tags: Phys Med Biol Source Type: research

Prediction of lung tumor motion using nonlinear autoregressive model with exogenous input.
Abstract The present note addresses the development of a lung tumor position predictor to be used in dynamic tumor tracking radiotherapy, abbreviated as DTT-RT. As there exists 50-500 ms positioning lag in the control of the multi-leaf collimator (MLC) of commercial medical linear accelerators, prediction of future lung tumor position with sufficiently long prediction horizon is inevitable for the successful implementation of DTT-RT. The present article proposes a lung tumor position predictor, which is classified as a nonlinear autoregressive model with exogenous input (NARX). The proposed predictor was trained u...
Source: Physics in Medicine and Biology - October 1, 2019 Category: Physics Authors: Jiang K, Fujii F, Shiinoki T Tags: Phys Med Biol Source Type: research

Intraoperative cone-beam CT spatial priors for diffuse optical fluorescence tomography.
Abstract A hybrid system for intraoperative cone-beam CT (CBCT) imaging and continuous-wave fluorescence tomography (FT) has been developed using an image-guidance framework. Intraoperative CBCT images with sub-millimeter spatial resolution are acquired with a flat-panel C-Arm. Tetrahedral meshes are generated from CBCT for finite element method implementation of diffuse optical tomography (NIRFAST). Structural data from CBCT is incorporated directly into the optical reconstruction process using Laplacian-type regularization ("soft spatial priors"). Experiments were performed using an in-house optical sy...
Source: Physics in Medicine and Biology - September 30, 2019 Category: Physics Authors: Daly MJ, Chan H, Muhanna N, Akens MK, Wilson BC, Irish JC, Jaffray DA Tags: Phys Med Biol Source Type: research

CNN-based PET sinogram repair to mitigate defective block detectors.
Abstract Positron emission tomography (PET) scanners continue to increase sensitivity and axial coverage by adding an ever expanding array of block detectors. As they age, one or more block detectors may lose sensitivity due to a malfunction or component failure. The sinogram data missing as a result thereof can lead to artifacts and other image degradations. We propose to mitigate the effects of malfunctioning block detectors by carrying out sinogram repair using a deep convolutional neural network. Experiments using whole-body patient studies with varying amounts of raw data removed are used to show that the neu...
Source: Physics in Medicine and Biology - September 30, 2019 Category: Physics Authors: Whiteley WJ, Gregor J Tags: Phys Med Biol Source Type: research

Spatially-variant image-based modeling of PSF deformations with application to a limited angle geometry from a dual-panel breast-PET imager.
Abstract Dual-panel PET system configuration can lead to spatially variable point-spread functions (PSF) of considerable deformations due to depth-of-interaction effects and limited angular coverage. If not modelled properly, these effects result in decreased and inconsistent recovery of lesion activity across the field-of-view (FOV), as well as mispositioning of lesions in the reconstructed image caused by strong PSF asymmetries. We implemented and evaluated models of such PSF deformations with spatially-variant image-based resolution modeling (IRM) within reconstruction (varRM) using the Direct Image REConstruct...
Source: Physics in Medicine and Biology - September 30, 2019 Category: Physics Authors: Gravel P, Surti S, Krishnamoorthy S, Karp JS, Matej S Tags: Phys Med Biol Source Type: research

A compact system for intraoperative specimen imaging based on edge illumination X-ray phase contrast.
Abstract A significant number of patients receiving breast-conserving surgery (BCS) for invasive carcinoma and ductal carcinoma in situ (DCIS) may need reoperation following tumor-positive margins from final histopathology tests. All current intraoperative margin assessment modalities have specific limitations. As a first step towards the development of a compact system for intraoperative specimen imaging based on edge illumination X-ray phase contrast, we prove that the system's dimensions can be reduced without affecting imaging performance. We analysed the variation in noise and contrast to noise ratio (CNR) wi...
Source: Physics in Medicine and Biology - September 30, 2019 Category: Physics Authors: Havariyoun G, Vittoria FA, Hagen CK, Basta D, Kallon GK, Endrizzi M, Massimi L, Munro PRT, Hawker S, Smit B, Astolfo A, Larkin O, Waltham RM, Shah Z, Duffy SW, Nelan R, Peel A, Suaris T, Jones LJ, Haig IG, Bate D, Olivo A Tags: Phys Med Biol Source Type: research