Deep feature regression (DFR) for 3D vessel segmentation.
In this study, a deep feature regression (DFR) method based on a convolutional regression network (CRN) and a stable point clustering mechanism for 3D vessel segmentation is proposed. First, the vessel model is constructed by a vessel section generator and a series of deviation parameter estimators. The generator provides 2D images for the training and prediction processes, while the estimators calculate pose parameters of an input vessel section. Second, estimators are trained by a series of CRNs, in which deep vessel features are automatically learned from 600,000 sample images. Third, we propose a stable point clusterin...
Source: Physics in Medicine and Biology - March 12, 2019 Category: Physics Authors: Zhao J, Ai D, Yang Y, Song H, Huang Y, Wang Y, Yang J Tags: Phys Med Biol Source Type: research

Automatic segmentation of levator hiatus from ultrasound images using U-net with dense connections.
Abstract In this paper, we propose a fully automatic method based on densely connected convolutional network for the segmentation of the levator hiatus from ultrasound images. A densely connected path is incorporated into a U-net to achieve a deep architecture and improve the segmentation performance. The proposed network architecture provides dense connections between layers that encourage feature reuse and reduce the number of parameters while maintaining good performance. The parameters of the network are optimized by training with a binary cross entropy i.e. logarithmic loss funct...
Source: Physics in Medicine and Biology - March 12, 2019 Category: Physics Authors: Li X, Hong Y, Kong D, Zhang X Tags: Phys Med Biol Source Type: research

Towards a second-generation PET/MR insert with enhanced timing and count rate performance.
Abstract Previously we have developed a first-generation PET insert prototype for small animal PET/MR imaging, which used resistor-based charge division multiplexing circuits and SensL B-series silicon photomultipliers (SiPMs). In this work we present results from a second-generation readout board with improved timing and count rate performance Three detector boards were tested: the first-generation readout board with SensL SPMArray4B (SiPM-B), the second-generation readout board with SensL ArrayC-30035-16P-PCB (SiPM-C) using the 'fast' outputs for timing, and the second generation board using Hamamatsu S11361-305...
Source: Physics in Medicine and Biology - March 12, 2019 Category: Physics Authors: Van Elburg DJ, Shrestha R, Goertzen AL Tags: Phys Med Biol Source Type: research

CT beam dosimetric characterization procedure for personalized dosimetry.
Abstract Personalized dosimetry in computed tomography (CT) can be realized by a full Monte Carlo (MC) simulation of the scan procedure. Essential input data needed for the simulation are appropriate CT x-ray source models and a model of the patients body which is based on the CT image. The purpose of this work is to develop comprehensive procedures for the determination of CT x-ray source models and their verication by comparison of calculated and measured dose distributions in physical phantoms. Mobile equipment together with customized software was developed and used for non-invasive determination of equivalent...
Source: Physics in Medicine and Biology - March 11, 2019 Category: Physics Authors: Rosendahl S, Bueermann L, Borowski M, Kortesniemi M, Sundell VM, Kosunen A, Siiskonen T Tags: Phys Med Biol Source Type: research

Time efficient scatter correction for time-of-flight PET: the immediate scatter approximation.
Abstract Utilization of Time-Of-Flight (TOF) information allows to improve image quality and convergence rate in iterative PET image reconstruction. In order to obtain quantitatively correct images accurate scatter correction (SC) is required that accounts for the non-uniform distribution of scatter events over the TOF bins. However, existing simplified TOF-SC algorithms frequently exhibit limited accuracy while the currently accepted gold standard - the TOF extension of the single scatter simulation approach (TOF-SSS) - is computationally demanding and can substantially slow down the reconstruction. In this paper...
Source: Physics in Medicine and Biology - March 11, 2019 Category: Physics Authors: Nikulin P, Maus J, Hofheinz F, Lougovski A, van den Hoff J Tags: Phys Med Biol Source Type: research

Feasibility of multi-atlas cardiac segmentation from thoracic planning CT in a probabilistic framework.
We present a probabilistic approach to segmentation, which provides a simple method to incorporate inter-observer variation, as well as a useful tool for evaluating the accuracy and sources of error in segmentation. A dataset consisting of 20 planning computed tomography images of Australian breast cancer patients with delineations of 17 structures (including whole heart, 4 chambers, coronary arteries and valves) was manually contoured by 3 independent observers, following a protocol based on a published reference atlas, with verification by a cardiologist. To develop and validate the segmentation framework a le...
Source: Physics in Medicine and Biology - March 11, 2019 Category: Physics Authors: Finnegan RN, Dowling JA, Koh ES, Tang S, Otton J, Delaney G, Batumalai V, Luo C, Atluri P, Satchithanandha A, Thwaites DI, Holloway L Tags: Phys Med Biol Source Type: research

Experimental validation of magnetically focused proton beams for radiosurgery.
Abstract We performed experiments using a triplet of quadrupole permanent magnets to focus protons and compared their dose distributions with unfocused collimated beams using energies and field sizes typically employed in proton radiosurgery. Experiments were performed in a clinical treatment room wherein small-diameter proton beams were focused by a magnet triplet placed immediately upstream of a water tank. The magnets consisted of segments of Sm<sub>2</sub>Co<sub>17</sub> rare-earth permanent magnetic material adhered into Halbach cylinders with nominal fi...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: McAuley GA, Teran AV, McGee PQ, Nyguen TT, Slater JM, Slater JD, Wroe AJ Tags: Phys Med Biol Source Type: research

Precise delineation and tumor localization based on novel image registration strategy between optical coherence tomography and computed tomography in the radiotherapy of intraocular cancer.
Abstract Radiation-associated toxicities due to sophisticated ocular anatomy and shape variability of organs at risk (OARs) are major concerns during external beam radiation therapy (EBRT) of patients with intraocular cancer. A novel two-step image registration strategy between optical coherence tomography (OCT) and computed tomography (CT) images was proposed and validated to precisely localize the target in the EBRT of patients with intraocular cancer. Specifically, multiple features from OCT and CT images were extracted automatically, then spatial transformation based on thin-plate spline function was performed...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Gong C, Shen M, Zheng X, Han C, Zhou Y, Xie C, Jin X Tags: Phys Med Biol Source Type: research

Dielectric properties of muscle and tissue-mimicking solutions for microwave medical imaging applications.
Abstract The aim of the present study was to synthesize mixture solutions which can accurately mimic the dielectric properties of biological tissues, specifically muscle and adipose tissues between 500 MHz and 50 GHz. Mixtures utilizing concentrations of bovine serum albumin (BSA) dissolved in phosphate buffered saline (PBS) and Ringer's solutions were synthesized to mimic in vivo and ex vivo muscle tissues. Solutions consisting of concentrations of peanut oil and Triton X 100 (TX) in PBS and Ringer's solutions were also synthesized to mimic in vivo and ex vivo adipose tissue. Results were then analysed and compar...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Pollacco DA, Caligari Conti M, Farrugia L, Schembri Wismayer P, Farina L, Sammut CV Tags: Phys Med Biol Source Type: research

Determination of ion recombination and polarity effect correction factors for a plane-parallel ionization Bragg Peak chamber under proton and carbon ion pencil beams.
Abstract Within the dosimetric characterization of particle beams, laterally-integrated depth-dose-distributions (IDDs) are measured and provided to the treatment planning system (TPS) for beam modeling or used as a benchmark for Monte Carlo (MC) simulations. The purpose of this work is the evaluation, in terms of ion recombination and polarity effect, of the dosimetric correction to be applied to proton and carbon ion curves as a function of linear energy transfer (LET). LET was calculated with a MC code for selected IDDs. Several regions of Bragg Peak (BP) curve were investigated. The charge was measured wi...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Mirandola A, Magro G, Maestri D, Mairani A, Mastella E, Molinelli S, Russo S, Vai A, Ciocca M Tags: Phys Med Biol Source Type: research

Single-arc VMAT optimization for dual-layer MLC.
In this study, we develop a novel single-arc VMAT optimization framework to take advantage of the unique DLMLC characteristics fully. Direct Aperture Optimization (DAO) for single-arc DLMLC VMAT was formulated as a least square dose fidelity objective, along with an anisotropic total variation term to regulate the fluence smoothness and a single segment term for forming simple apertures. The DAO was solved through alternating optimization approach. The DLMLC deliverability constraint and the MLC leaf speed constraint were formulated as the optimization constraints and solved using a graph optimization algorithm. Feasibilit...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Lyu Q, Neph R, Yu VY, Ruan D, Sheng K Tags: Phys Med Biol Source Type: research

Synthetic 4D-CT of the thorax for treatment plan adaptation on MR-guided radiotherapy systems.
Abstract MR-guided radiotherapy treatment planning utilises the high soft-tissue contrast of MRI to reduce uncertainty in delineation of the target and organs at risk. Replacing 4D-CT with MRI-derived synthetic 4D-CT would support treatment plan adaptation on hybrid MR-guided radiotherapy systems for inter- and intrafractional differences in anatomy and respiration, whilst mitigating the risk of CT to MRI registration errors. Three methods were devised to calculate synthetic 4D and midposition (time-weighted mean position of the respiratory cycle) CT from 4D-T1w and Dixon MRI. The first approach employe...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Freedman JN, Bainbridge H, Nill S, Collins DJ, Kachelriess M, Leach MO, McDonald F, Oelfke U, Wetscherek A Tags: Phys Med Biol Source Type: research

pGPUMCD: an efficient GPU-based Monte Carlo code for accurate proton dose calculations.
e;s P Abstract In proton therapy, Monte Carlo simulations are desirable to accurately predict the delivered dose. This paper introduces and benchmarks pGPUMCD, a GPU-based Monte Carlo code implementing the physical processes required for protontherapy applications. In pGPUMCD, the proton transport is carried out in a voxelized geometry with a class II condensed history scheme. For this purpose, the equivalent restricted stopping power formalism (L<sub>eq</sub> formalism), the Fermi-Eyges scattering theory and the discrete electromagnetic/nuclear interactions were considered. pGPUMCD was...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Maneval D, Ozell B, Després P Tags: Phys Med Biol Source Type: research

Fast gamma-ray interaction-position estimation using k-d tree search.
Abstract We have developed a fast gamma-ray interaction-position estimation method using k-d tree search, which can be combined with various kinds of closeness metrics such as Euclidean distance, maximum-likelihood estimation, etc.. Compared with traditional search strategies, this method can achieve both speed and accuracy at the same time using the k-d tree data structure. The k-d tree search method has a time complexity of O(log2(N)), where N is the number of entries in the reference data set, which means large reference datasets can be used to efficiently estimate each event's interaction position. This method...
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Li X, Tao L, Levin CS, Furenlid LR Tags: Phys Med Biol Source Type: research

Higher SNR PET image prediction using a deep learning model and MRI image.
Conclusions Our proposed method could improve the PET SNR without having higher SNR PET images. . PMID: 30844784 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 7, 2019 Category: Physics Authors: Liu CC, Qi J Tags: Phys Med Biol Source Type: research

Intravascular optical coherence tomography to validate finite-element simulation of angioplasty balloon inflation.
Abstract Concrete methods are lacking to examine angioplasty simulation results. For the first time, we explored the application of intravascular optical coherence tomography (IVOCT) to experimentally validate results obtained from finite-element simulation of angioplasty balloon deployment. In order to simulate each experimental scenario, IVOCT images were used to create initial geometrical models for the balloon and the phantoms. The study comprised three scenarios. The first scenario involved experimentally monitoring as well as simulating free expansion of the balloon. The second scenario involved experimental...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Azarnoush H, Pazos V, Vergnole S, Boulet B, Lamouche G Tags: Phys Med Biol Source Type: research

Four-dimensional digital tomosynthesis image reconstruction using brute force-based adaptive total variation (BF-ATV) in a prototype LINAC system.
In conclusion, the proposed low-dose 4D-DTS reconstruction scheme may provide better performance due in part to its rapid scanning. Therefore, it is potentially applicable to practical 4D imaging for radiotherapy. PMID: 30840940 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Choi S, Lee S, Kang YN, Hsieh SS, Kim HJ Tags: Phys Med Biol Source Type: research

A comparative study of information retrieval in grating-based X-ray phase-contrast imaging.
Abstract The cosine-model analysis (CMA) method and the small angle X-ray scattering (SAXS) method are two major types of information retrieval algorithms, commonly utilized in X-ray phase-contrast imaging with a grating interferometer. However, there are significant differences between the two methods in algorithm implementation, and the existing literature has not completely revealed their intrinsic relationship. In this paper, we theoretically derive and experimentally verify the intrinsic connections between CMA and SAXS, and it is seen that SAXS can be interpreted well by the cosine-model assumption of CMA. T...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Li X, Gao H, Chen Z, Zhang L, Zhu X, Wang S, Peng W Tags: Phys Med Biol Source Type: research

Evaluation of ge-doped silica fibre TLDs for < i > in vivo < /i > dosimetry during intraoperative radiotherapy.
In this study, using the INTRABEAM® system, investigation was made of the potential application of GDSF TLDs for in vivo IORT dosimetry. The GDSFs were calibrated over the respective dose- and depth-range 1 to 20 Gy and 3 to 45 mm from the X-ray probe. The effect of different sizes of spherical applicator on TL response of the fibres was also investigated. The results show the GDSF TLDs to be applicable for IORT dose assessment, with the important incorporated correction for beam quality effects using different spherical applicator sizes. The total uncertainty in use of this type of GDSF for dosimetry has been found to...
Source: Physics in Medicine and Biology - March 6, 2019 Category: Physics Authors: Moradi F, Ung NM, Mahdiraji GA, Khandaker MU, See MH, Mohd Taib NA, Bradley DA Tags: Phys Med Biol Source Type: research

Hydrogels as a water bolus during hyperthermia treatment.
m A Abstract The feasibility of using hydrogels as a water bolus during hyperthermia treatment was assessed. Three types of gels, high methoxyl (HM) pectin/alginate, xanthan/locust bean gum (LBG) and xanthan/LBG/agarose were evaluated based on their dielectric properties, rheological and mechanical properties. The most suitable, xanthan/LBG/agarose, gel was further used as a water bolus in a hyperthermia array applicator. The gels composed of polysaccharides carrying low charge displayed dielectric properties close to those of water, while the dielectric properties of HM pectin/alginate gel was deemed unsuitable&#...
Source: Physics in Medicine and Biology - March 4, 2019 Category: Physics Authors: Dobsicek Trefna H, Ström A Tags: Phys Med Biol Source Type: research

Event-by-event non-rigid data-driven PET respiratory motion correction methods: comparison of principal component analysis and centroid of distribution.
Abstract Respiratory motion is a major cause of degradation of PET image quality. Respiratory gating and motion correction can be performed to reduce the effects of respiratory motion; these methods require motion information, typically obtained from external tracking systems. Various groups have studied data-driven (DD) motion estimation methods. Recently, a data-driven respiratory motion estimation method was established by calculating the centroid of distribution (COD) of listmode events, which was then used with event-by-event respiratory motion correction (EBE-MC), and showed results comparable to those with ...
Source: Physics in Medicine and Biology - March 1, 2019 Category: Physics Authors: Ren S, Lu Y, Bertolli O, Thielemans K, Carson RE Tags: Phys Med Biol Source Type: research

Influence of cone beam CT (CBCT) scan parameters on size specific dose estimate (SSDE): A Monte Carlo study.
Abstract The CT dose index (CTDI&lt;sub&gt;vol&lt;/sub&gt;) is the dosimetric quantity used for multi-slice CT (MSCT) with beams ≤4 cm. Conversion factors (f&lt;sub&gt;size&lt;/sub&gt;) based on patient size are applied to CTDI&lt;sub&gt;vol&lt;/sub&gt; to adjust for differences in patient size and derive size-specific dose estimates (SSDE) relating to patient dose. The aim of this study is to: (1) investigate use of a similar technique to provide SSDE values for cone beam CT (CBCT) scans, (2) determine whether factors derived for narrow beam MSCT are suitable for...
Source: Physics in Medicine and Biology - March 1, 2019 Category: Physics Authors: Abuhaimed A, Martin CJ, Demirkaya O Tags: Phys Med Biol Source Type: research

VirtualDose-IR: A cloud-based software for reporting organ doses in interventional radiology.
Abstract A cloud-based software, VirtualDose-IR, designed to report organ doses and effective doses for a diverse patient population from interventional radiology (IR) procedures has been developed and tested. This software is based on a comprehensive database of Monte Carlo-generated organ dose built with a set of 21 anatomically realistic patient phantoms. The patient types included in this database are both male and female people with different ages reflecting reference adults, obese people with different BMIs and pregnant women at different gestational stages. Selectable parameters such as patient type, tube v...
Source: Physics in Medicine and Biology - March 1, 2019 Category: Physics Authors: Huo W, Pi Y, Feng M, Qi Y, Gao Y, Caracappa PF, Chen Z, Xu XG Tags: Phys Med Biol Source Type: research

Mesh-type reference Korean phantoms (MRKPs) for adult male and female for use in radiation protection dosimetry.
Abstract In the present study, to overcome the limitations of the previous voxel-type reference computational phantoms, a pair of new reference Korean phantoms, called mesh-type reference Korean phantoms (MRKPs), were developed for the adult male and female in a high-quality/fidelity mesh format. The developed phantoms include all target and source regions required for effective dose calculation, even micrometer-scale target and source regions of the respiratory and alimentary tract organs, skin, urinary bladder, and eye lens. The developed phantoms, which are in the mesh format, can be directly used in Monte Carl...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Choi C, Nguyen TT, Yeom YS, Lee H, Han H, Shin B, Zhang X, Kim CH, Chung BS Tags: Phys Med Biol Source Type: research

MRI-based synthetic CT generation using semantic random forest with iterative refinement.
Abstract Target delineation for radiation therapy treatment planning often benefits from magnetic resonance imaging (MRI) in addition to x-ray computed tomography (CT) due to MRI's superior soft tissue contrast. MRI-based treatment planning could reduce systematic MR-CT co-registration errors, medical cost, radiation exposure, and simplify clinical workflow. However, MRI-only based treatment planning is not widely used to date because treatment-planning systems rely on the electron density information provided by CTs to calculate dose. Additionally, air and bone regions are difficult to separategiven their similar...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Lei Y, Harms JM, Wang T, Tian S, Zhou J, Shu HK, Zhong J, Mao H, Curran WJ, Liu T, Yang X Tags: Phys Med Biol Source Type: research

Stochastic frontier analysis as knowledge-based model to improve sparing of organs-at-risk for VMAT-treated prostate cancer.
Abstract Stochastic frontier analysis is used as a novel knowledge-based technique in order to develop a predictive model of dosimetric features from signicant geometric parameters describing a patient morphology. 406 patients treated with VMAT for prostate cancer were analyzed retrospectively. Cases were divided into three prescription-based groups. Seven geometric parameters are extracted to characterize the relationship between the organs-at-risk (bladder and rectum) with the planning volume (PTV). In total, 37 dosimetric parameters are tested for these two OARs. Stochastic frontier analysis allows the determin...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Kroshko A, Morin O, Archambault L Tags: Phys Med Biol Source Type: research

Development of multi-purpose 3D printed phantoms for MRI.
Abstract This work describes the development and application of 3D printed MRI phantoms. Unlike traditional phantoms these test objects are made from solid materials which can be imaged directly without filling. The models were manufactured using both MRI visible and invisible materials. The MRI visible materials were imaged on a 3T system to quantify their T1 and T2 properties and CT to quantify the electron density. Three phantoms are described: A distortion phantom was imaged on an open bore MRI system to assess distortion over a 30 cm field-of-view; A solid tumour model was imaged using a motion simulator and ...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Rai R, Wang YF, Manton D, Dong B, Deshpande S, Liney GP Tags: Phys Med Biol Source Type: research

Automatic PET cervical tumor segmentation by combining deep learning and anatomic prior.
Abstract Cervical tumor segmentation on 3D &lt;sup&gt;18&lt;/sup&gt;FDG PET images is a challenging task because of the proximity between cervix and bladder, both of which can uptake &lt;sup&gt;18&lt;/sup&gt;FDG tracers. This problem makes traditional segmentation based on intensity variation methods ineffective and reduces overall accuracy. Based on anatomy knowledge, including "roundness" of the cervical tumor and relative positioning between the bladder and cervix, we propose a supervised machine learning method that integrates convolutional neural network (CNN) with th...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Chen L, Shen C, Zhou Z, Maquilan G, Albuquerque K, Folkert MR, Wang J Tags: Phys Med Biol Source Type: research

Comment on 'Linear energy transfer incorporated intensity modulated proton therapy optimization'.
Abstract Cao et al (2018) published an article on inverse planning based on dose-averaged linear energy transfer (LET). Their claim that the problem can be cast as a linear optimization model relies on an incorrect application of the Charnes-Cooper transformation. In this comment we show that their linear model is simlar to one where dose-averaged LET is multiplied with dose, explaining why their model was nonetheless able to improve the LET distribution. PMID: 30811348 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 27, 2019 Category: Physics Authors: Gorissen BL Tags: Phys Med Biol Source Type: research

Reply to Comment on 'Linear energy transfer incorporated intensity modulated proton therapy optimization'.
Abstract In this reply we present additional description of our linear model for LET optimization in response to the comments by Dr Gorissen. We clarify that this model cannot guarantee global optimal solutions to the sum-of-fractions problem. Based on our data, it could be used to optimize LET efficiently while dose constraints are maintained. PMID: 30811349 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 27, 2019 Category: Physics Authors: Cao W, Khabazian A, Yepes P, Lim G, Poenisch F, Grosshans D, Mohan R Tags: Phys Med Biol Source Type: research

BrachyView: initial preclinical results for a real-time in-body HDR PBT source tracking system with simultaneous TRUS image fusion.
Abstract A prototype in-body gamma camera system with integrated trans-rectal ultrasound (TRUS) and associated real-time image acquisition and analysis software was developed for intraoperative source tracking in high dose rate (HDR) brachytherapy. The accuracy and temporal resolution of the system was validated experimentally using a deformable tissue-equivalent prostate gel phantom and a full clinical HDR treatment plan. The BrachyView system was able to measure 78% of the 200 source positions with an accuracy of better than 1 mm. A minimum acquisition time of 0.28 s/frame was required to achieve this accuracy, ...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Alnaghy S, Cutajar DL, Safavi-Naeini M, George S, Howie A, Bece A, Bucci JA, Jakubek J, Pospisil S, Lerch MLF, Petasecca M, Rozenfeld AB Tags: Phys Med Biol Source Type: research

Dosimetric accuracy of dynamic couch rotation during volumetric modulated arc therapy (DCR-VMAT) for primary brain tumours.
Abstract Radiotherapy treatment plans using dynamic couch rotation during volumetric modulated arc therapy (DCR-VMAT) reduce the dose to organs at risk (OARs) compared to coplanar VMAT, while maintaining the dose to the planning target volume (PTV). This paper seeks to validate this finding with measurements. DCR-VMAT treatment plans were produced for five patients with primary brain tumours and delivered using a commercial linear accelerator (linac). Dosimetric accuracy was assessed using point dose and radiochromic film measurements. Linac- recorded mechanical errors were assessed by extracting deviations from l...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Smyth G, Evans PM, Bamber JC, Mandeville HC, Moore AR, Welsh LC, Saran FH, Bedford JL Tags: Phys Med Biol Source Type: research

Monte Carlo simulations of out-of-field surface doses due to the electron streaming effect in orthogonal magnetic fields.
Abstract The out-of-field surface dose contribution due to backscattered or ejected electrons, contained by the magnetic field, is evaluated in this work. This electron streaming effect (ESE) can contribute to out-of-field skin doses and toxicity in orthogonal magnetic resonance guided radiation therapy machines. Using the EGSnrc Monte Carlo package, a central phantom is set-up with an incident 10X10cm&lt;sup&gt;2&lt;/sup&gt; 7MV FFF photon beam. The phantom exit or entry surface is inclined with respect to the magnetic field, and an out-of-field water panel is positioned 10cm away from...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Malkov VN, Hackett SL, Wolthaus JWH, Raaymakers BW, van Asselen B Tags: Phys Med Biol Source Type: research

Uniqueness of poroelastic and viscoelastic nonlinear inversion MR elastography at low frequencies.
Abstract Intrinsic actuation MR Elastography (IA-MRE) exploits natural pulsations of the brain as a motion source to estimate mechanical property maps. The low frequency motion of IA-MRE introduces new considerations for inversion algorithms relative to traditional external actuation MRE. Specifically, inertial forces become very small, which leaves low frequency viscoelastic inversions with a non-unique scalar multiplier. Biphasic poroelastic inversions include additional fluid-solid interaction forces to balance the elastic forces, which avoids the non-uniqueness. Analyzing the convergence behavior from differen...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: McGarry MDJ, Van Houten E, Solamen L, Gordon-Wylie S, Weaver J, Paulsen KD Tags: Phys Med Biol Source Type: research

A segmentation method combining probability map and boundary based on multiple fully convolution network and repetitive training.
Abstract Cell nuclei image segmentation technology can help researchers observe each cell's stress response to drug treatment. However, it is still a challenge to accurately segment the adherent cell nuclei. At present, image segmentation based on fully convolutional network (FCN) is attracting researcher's attention. We propose a Multiple FCN architecture and Repetitive Training (M-FCN-RT) method to learn features of cell nucleus images. In M-FCN-RT, the Multiple FCN (M-FCN) architecture is composed of several Single FCNs (S-FCN) with the same structure, and each FCN is used to learn the specific features of imag...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Yin W, Hu Y, Yi S, He J Tags: Phys Med Biol Source Type: research

Impact of TPS calculation algorithms on dose delivered to the patient in proton therapy treatments.
Conclusion: Different TPS dose calculation approaches mainly affected dose delivered in H&N proton treatments, while minor deviations were found for pelvic tumors. RS-MC proved to be the most accurate TPS dose calculation algorithm when compared to an independent MC simulation code. PMID: 30802887 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 25, 2019 Category: Physics Authors: Molinelli S, Russo S, Magro G, Maestri D, Mairani A, Mastella E, Mirandola A, Vai A, Vischioni B, Valvo F, Ciocca M Tags: Phys Med Biol Source Type: research

Fiducial marker based intra-fraction motion assessment on cine-MR for MR-Linac treatment of prostate cancer.
Conclusion We have developed a robust, fast and accurate FM tracking algorithm for cine-MR data, which allows for continuous monitoring of prostate motion during MR-guided radiotherapy (MRgRT). These results will be used to validate automatic prostate tracking based on soft-tissue contrast. PMID: 30794995 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 22, 2019 Category: Physics Authors: de Muinck Keizer DM, Pathmanathan AU, Andreychenko A, Kerkmeijer LGW, van der Voort van Zyp JRN, Tree AC, Van den Berg CAT, de Boer JCJ Tags: Phys Med Biol Source Type: research

Posture-dependent dose coefficients of mesh-type ICRP reference computational phantoms for photon external exposures.
Abstract Recently, the International Commission on Radiological Protection (ICRP) developed new mesh-type reference computational phantoms (MRCPs) that provide high deformability compared with the current voxel-type reference computational phantoms of ICRP Publication 110. Taking advantage of this deformability, in the present study, the MRCPs were deformed to five non-standing postures (i.e., walking, sitting, bending, kneeling, and squatting) by developing and using a systematic posture-change method based on the as-rigid-as-possible (ARAP) shape-deformation algorithm and motion-capture technology. The non-stand...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Yeom YS, Han H, Choi C, Nguyen TT, Shin B, Lee C, Kim CH Tags: Phys Med Biol Source Type: research

Computational modelling of resistance and associated treatment response heterogeneity in metastatic cancers.
Abstract Metastatic cancer patients invariably develop treatment resistance. Different levels of resistance lead to observed heterogeneity in treatment response. The main goal was to evaluate treatment response heterogeneity with computation model simulating dynamics of drug-sensitive and drug-resistant cells. Model parameters included proliferation, drug induced death, transition and proportion of intrinsically resistant cells. Model was benchmarked with imaging metric extracted from 39 metastatic prostate cancer patients who had 18F-NaF-PET/CT scans performed at baseline and three cycles into chemotherapy or hor...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Turk M, Simoncic U, Roth A, Valentinuzzi D, Jeraj R Tags: Phys Med Biol Source Type: research

Integrating DVH criteria into a column generation algorithm for VMAT treatment planning.
Abstract Volumetric-modulated arc therapy (VMAT) treatment planning is an efficient treatment technique with a high degree of flexibility in terms of dose rate, gantry speed, and aperture shapes during rotation around the patient. However, the dynamic nature of VMAT results in a large-scale nonconvex optimization problem. Determining the priority of the tissues and voxels to obtain clinically acceptable treatment plans poses additional challenges for VMAT optimization. The main purpose of this paper is to develop an automatic planning approach integrating dose-volume histogram (DVH) criteria in direct aperture opt...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Mahnam M, Gendreau M, Lahrichi N, Rousseau LM Tags: Phys Med Biol Source Type: research

Oblique raster scanning: an ion dose delivery procedure with variable energy layers.
Abstract In ion Therapy Accelerator Complexes the dose is delivered "actively" by subdividing the target in Equal Energy Layers, which are scanned by a beam spot visiting in sequence the planned spots, previously defined by the Treatment Planning System. Synchrotrons-based complexes have three problems: (i) the switching from the energy needed to scan one Equal Energy Layer to the next takes time, an effect that is more relevant for the very short treatment times now often required; (ii) the unavoidable "ripples" of the quadrupoles and bending magnets currents produce large erratic time variati...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Amaldi U Tags: Phys Med Biol Source Type: research

A cone-shaped gradient coil design for high-resolution MRI head imaging.
Abstract Insertable head gradient coils offer significant advantages such as high gradient strength and fast gradient switching speed owing to close distance to the target region of interest than whole-body cylindrical coils. To produce superior gradient performance, the local head coil is typically designed with an asymmetric configuration to accommodate both the shoulders and head of a patient, leading to tough dimensional constraints and practical limits to the coil implementation. In this paper, we proposed a new cone-shaped model to improve the performance of the asymmetric head coils and also to mitigate pat...
Source: Physics in Medicine and Biology - February 19, 2019 Category: Physics Authors: Tang F, Hao J, Freschi F, Niu C, Repetto M, Liu F, Crozier S Tags: Phys Med Biol Source Type: research

Combining many-objective radiomics and 3-dimensional convolutional neural network through evidential reasoning to predict lymph node metastasis in head and neck cancer.
Abstract Lymph node metastasis (LNM) is a significant prognostic factor in patients with head and neck cancer, and the ability to predict it accurately is essential to optimizing treatment. Positron emission tomography (PET) and computed tomography (CT) imaging are routinely used to identify LNM. Although large or highly active lymph nodes (LNs) have a high probability of being positive, identifying small or less reactive LNs is challenging. The accuracy of LNM identification strongly depends on the physician's experience, so an automatic prediction model for LNM based on CT and PET images is warranted to assist L...
Source: Physics in Medicine and Biology - February 19, 2019 Category: Physics Authors: Chen L, Zhou Z, Sher D, Zhang Q, Shah J, Pham NL, Jiang SB, Wang J Tags: Phys Med Biol Source Type: research

McSART: an iterative model-based, motion-compensated SART algorithm for CBCT reconstruction.
Abstract 4D cone beam computed tomography (CBCT) images of the thorax and abdomen can have reduced quality due to the limited number of projections per respiratory bin used in gated image reconstruction. In this work, we present a new algorithm to reconstruct high quality CBCT images by simultaneously reconstructing images and generating an associated respiratory motion model. This is done by updating model parameters to compensate for motion during the iterative image reconstruction process. CBCT image acquisition was simulated using the digital eXternal CArdiac Torso (XCAT) phantom, simulating breathing motion u...
Source: Physics in Medicine and Biology - February 18, 2019 Category: Physics Authors: Chee G, O'Connell D, Yang Y, Singhrao K, Low DA, Lewis JH Tags: Phys Med Biol Source Type: research

A mixed-integer linear programming optimization model framework for capturing expert planning style in low dose rate prostate brachytherapy.
Abstract Low dose rate (LDR) brachytherapy is a minimally invasive form of radiation therapy, used to treat prostate cancer, and it involves permanent implantation of radioactive sources (seeds) inside of the prostate gland. Treatment planning in brachytherapy involves a decision making process for the placement of the sources in order to deliver an effective dose of radiation to cancerous tissue in the prostate while sparing the surrounding healthy tissue. Such a decision making process can be modeled as a mixed-integer linear programming (MILP) problem. In this paper, we introduce a novel MILP optimization model...
Source: Physics in Medicine and Biology - February 15, 2019 Category: Physics Authors: Babadagli ME, Sloboda R, Doucette J Tags: Phys Med Biol Source Type: research

2019: An Update from the Editor-in-Chief.
Abstract Not applicable. PMID: 30754025 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 12, 2019 Category: Physics Authors: Cherry SR Tags: Phys Med Biol Source Type: research

Investigation of the refractive index decrement of 3D printing materials for manufacturing breast phantoms for phase contrast imaging.
Abstract 3D breast modelling for 2D and 3D breast X-ray imaging would benefit from the availability of digital and physical phantoms that reproduce accurately the complexity of the breast anatomy. While a number of groups have produced digital phantoms with increasing level of complexity, physical phantoms reproducing that software approach have been scarcely developed. One possibility is offered by 3D printing technology. This implies the assessment of the energy dependent absorption index β of 3D printing materials for absorption based imaging, as well as the assessment of the refractive index decrement, &d...
Source: Physics in Medicine and Biology - February 12, 2019 Category: Physics Authors: Esposito G, Mettivier G, Bliznakova K, Bliznakov Z, Bosmans H, Bravin A, Buliev I, Di Lillo F, Ivanov D, Minutillo M, Sarno A, Vignero J, Russo P Tags: Phys Med Biol Source Type: research

Real-time respiratory triggered four dimensional cone-beam CT halves imaging dose compared to conventional 4D CBCT.
Abstract Four dimensional cone-beam computed tomography (4D CBCT) improves patient positioning and the accuracy of radiation therapy for patients with mobile tumours. Generally, 4D CBCT requires many hundreds of x-ray projections to measure target trajectories and the imaging frequency is not adapted to the patient's respiratory signal resulting in over-sampling. In contrast, respiratory triggered 4D CBCT (RT 4D CBCT) is an acquisition technique that has been experimentally implemented and has shown to reduce the number of x-ray projections and thus 4D CBCT dose with minimal impact on image quality. The aim of thi...
Source: Physics in Medicine and Biology - February 12, 2019 Category: Physics Authors: Cooper BJ, O'Brien RT, Shieh CC, Keall PJ Tags: Phys Med Biol Source Type: research

Joint correction of attenuation and scatter in image space using deep convolutional neural networks for dedicated brain < sup > 18 < /sup > F-FDG PET.
In conclusion, we demonstrated the feasibility of directly producing PET images corrected for attenuation and scatter using a DCNN (PET&lt;sub&gt;DCNN&lt;/sub&gt;) from PET&lt;sub&gt;NC&lt;/sub&gt; in image space without requiring conventional attenuation map generation and time-consuming scatter correction. Additionally, our DCNN-based method provides a possible alternative to MR-ASC for simultaneous PET/MRI. PMID: 30743246 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 11, 2019 Category: Physics Authors: Yang J, Park D, Gullberg GT, Seo Y Tags: Phys Med Biol Source Type: research

Relationship between power density and surface temperature elevation for human skin exposure to electromagnetic waves with oblique incidence angle from 6 GHz to 1 THz.
This study presents an investigation of human skin exposure to obliquely incident electromagnetic waves at frequencies from 6 GHz to 1 THz. We aim to clarify the relationship between the power density and the skin surface temperature elevation under various exposure conditions. A Monte Carlo simulation was conducted to assess the transmittance and surface temperature elevation considering the variation of skin tissue thickness. For the case of TM wave injection, transmittance increases with increasing incidence angle from the normal incidence because of the Brewster effect. The normal incidence is confirmed as the worst-ca...
Source: Physics in Medicine and Biology - February 8, 2019 Category: Physics Authors: Li K, Sasaki K, Watanabe S, Shirai H Tags: Phys Med Biol Source Type: research