Independent dose verification system with Monte Carlo simulations using TOPAS for passive scattering proton therapy at the National Cancer Center in Korea.
Abstract For the independent validation of treatment plans, we developed a Monte Carlo (MC)-based patient dose calculation system with the tool for particle simulation (TOPAS) to enable routine and automatic dose recalculation for each patient. The proton beam nozzle was modeled with TOPAS to simulate the therapeutic beam, and MC commissioning was performed by comparing percent depth dose with the measurement. The beam set-up based on the prescribed beam range and modulation width was automated by modifying the vendor-specific method. The CT phantom was modeled based on the DICOM CT files with TOPAS-built-in funct...
Source: Physics in Medicine and Biology - August 15, 2017 Category: Physics Authors: Shin WG, Testa M, Kim HS, Jeong JH, Lee SB, Kim YJ, Min CH Tags: Phys Med Biol Source Type: research
Impact of field number and beam angle on functional image-guided lung cancer radiotherapy planning.
Abstract To investigate the effect of beam angles and field number on functionally-guided intensity modulated radiotherapy (IMRT) normal lung avoidance treatment plans that incorporate hyperpolarised helium-3 magnetic resonance imaging ((3)He MRI) ventilation data. Eight non-small cell lung cancer patients had pre-treatment (3)He MRI that was registered to inspiration breath-hold radiotherapy planning computed tomography. IMRT plans that minimised the volume of total lung receiving ⩾20 Gy (V20) were compared with plans that minimised (3)He MRI defined functional lung receiving ⩾20...
Source: Physics in Medicine and Biology - August 11, 2017 Category: Physics Authors: Tahir BA, Bragg CM, Wild JM, Swinscoe JA, Lawless SE, Hart KA, Hatton MQ, Ireland RH Tags: Phys Med Biol Source Type: research
Representing the dosimetric impact of deformable image registration errors.
In this study, landmarked images were used to characterize the DIR error throughout an image space and determine its impact on dosimetric analysis. Ten thoracic 4DCT images with 300 landmarks per image study matching the end-inspiration and end-expiration phases were obtained from 'dir-labs'. DIR was performed using commercial software MIM Maestro. The range of dose uncertainty (RDU) was calculated at each landmark pair as the maximum and minimum of the doses within a sphere around the landmark in the end-expiration phase. The radius of the sphere was defined by a measure of DIR error which included either the actual DIR e...
Source: Physics in Medicine and Biology - August 11, 2017 Category: Physics Authors: Vickress J, Battista J, Barnett R, Yartsev S Tags: Phys Med Biol Source Type: research
Intraventricular vector flow mapping-a Doppler-based regularized problem with automatic model selection.
Abstract We propose a regularized least-squares method for reconstructing 2D velocity vector fields within the left ventricular cavity from single-view color Doppler echocardiographic images. Vector flow mapping is formulated as a quadratic optimization problem based on an [Formula: see text]-norm minimization of a cost function composed of a Doppler data-fidelity term and a regularizer. The latter contains three physically interpretable expressions related to 2D mass conservation, Dirichlet boundary conditions, and smoothness. A finite difference discretization of the continuous problem was adopted in a polar coo...
Source: Physics in Medicine and Biology - August 11, 2017 Category: Physics Authors: Assi KC, Gay E, Chnafa C, Mendez S, Nicoud F, Abascal JFPJ, Lantelme P, Tournoux F, Garcia D Tags: Phys Med Biol Source Type: research
Monte Carlo and experimental determination of correction factors for gamma knife perfexion small field dosimetry measurements.
Abstract Detector-, field size- and machine-specific correction factors are required for precise dosimetry measurements in small and non-standard photon fields. In this work, Monte Carlo (MC) simulation techniques were used to calculate the correction factors for a series of ionization chambers, a synthetic microDiamond and diode dosimeters, used for reference and/or output factor (OF) measurements in the Gamma Knife Perfexion photon fields. Calculations were performed for the Solid Water (SW) and ABS plastic phantoms, as well as for a water phantom of the same geometry. MC calculations for OF-measurements correct...
Source: Physics in Medicine and Biology - August 10, 2017 Category: Physics Authors: Zoros E, Moutsatsos AS, Pappas EP, Georgiou E, Kollias G, Karaiskos P, Pantelis E Tags: Phys Med Biol Source Type: research
Magnetic targeting to enhance microbubble delivery in an occluded microarterial bifurcation.
This study examines the obstacles to delivery posed by fluid dynamic conditions in occluded vasculature and investigates whether magnetic targeting can improve microbubble delivery. A two-dimensional computational fluid dynamic (CFD) model of a fully occluded Y-shaped microarterial bifurcation was developed to determine: (i) the fluid dynamic field in the vessel with inlet velocities from 1-100mm/s (corresponding to Reynolds numbers 0.25-25); (ii) the transport dynamics of fibrinolytic drugs; and (iii) the flow behavior of microbubbles with diameters in the clinically-relevant range (0.6-5μm). In vitro experiments were ...
Source: Physics in Medicine and Biology - August 10, 2017 Category: Physics Authors: de Saint Victor M, Carugo D, Barnsley LC, Owen J, Coussios CC, Stride E Tags: Phys Med Biol Source Type: research
On the use of particle filters for electromagnetic tracking in high dose rate brachytherapy.
We present a hybrid data analysis system which combines multi-dimensional scaling with particle filters to precisely determine sensor dwell positions in the catheters during subsequent radiation treatment sessions. Both techniques are complemented with empirical mode decomposition for the removal of superimposed breathing artifacts. We show that the hybrid model robustly and reliably determines the spatial positions of all catheters used during the treatment and precisely determines any deviations of actual sensor dwell positions from the treatment plan. The hybrid system only relies on sensor positions measured with...
Source: Physics in Medicine and Biology - August 10, 2017 Category: Physics Authors: Götz TI, Lahmer G, Brandt T, Kallis K, Strnad V, Bert C, Hensel B, Tome AM, Lang EW Tags: Phys Med Biol Source Type: research
Simultaneous calibration phantom commission and geometry calibration in cone beam CT.
Abstract Geometry calibration is a vital step for describing the geometry of a cone beam computed tomography (CBCT) system and is a prerequisite for CBCT reconstruction. In current methods, calibration phantom commission and geometry calibration are divided into two independent tasks. Small errors in ball-bearing (BB) positioning in the phantom-making step will severely degrade the quality of phantom calibration. To solve this problem, we propose an integrated method to simultaneously realize geometry phantom commission and geometry calibration. Instead of assuming the accuracy of the geometry phantom, the integra...
Source: Physics in Medicine and Biology - August 9, 2017 Category: Physics Authors: Xu Y, Yang S, Ma J, Li B, Wu S, Qi H, Zhou L Tags: Phys Med Biol Source Type: research
Is the PTW 60019 microDiamond a suitable candidate for small field reference dosimetry?
Abstract A systematic study of the PTW microDiamond (MD) output factors (OF) is reported, aimed at clarifying its response in small fields and investigating its suitability for small field reference dosimetry. Ten MDs were calibrated under (60)Co irradiation. OF measurements were performed in 6 MV photon beams by a CyberKnife M6, a Varian DHX and an Elekta Synergy linacs. Two PTW silicon diodes E (Si-D) were used for comparison. The results obtained by the MDs were evaluated in terms of absorbed dose to water determination in reference conditions and OF measurements, and compared to the results reported in the rec...
Source: Physics in Medicine and Biology - August 9, 2017 Category: Physics Authors: De Coste V, Francescon P, Marinelli M, Masi L, Paganini L, Pimpinella M, Prestopino G, Russo S, Stravato A, Verona C, Verona-Rinati G Tags: Phys Med Biol Source Type: research
Human exposure to pulsed fields in the frequency range from 6 to 100 GHz.
This study investigated how the temperature rise was affected by exposure duration at frequencies higher than 6 GHz. Far-field exposure of the human face to pulses shorter than 10 s at frequencies from 6 to 100 GHz was modelled using the finite-difference time-domain method. The bioheat transfer equation was used for thermal modelling. We investigated the effects of frequency, polarization, exposure duration, and depth below the skin surface on the temperature rise. The results indicated limitations in the current human exposure guidelines and showed that radiant exposure, i.e. energy absorption per unit area, can b...
Source: Physics in Medicine and Biology - August 9, 2017 Category: Physics Authors: Laakso I, Morimoto R, Heinonen J, Jokela K, Hirata A Tags: Phys Med Biol Source Type: research
Improving the gamma analysis comparison using an unbinned multivariate test.
In this study we present a new procedure for the comparison of two dose matrices by means of a statistical test. A statistical distance is proposed to decide whether the difference between the two matrices is statistically significant. This statistical test is based on the square difference between the experimental and expected gamma matrix results. The expected gamma matrix is calculated by simulating the measurement process. The criteria for significance is chosen to give the same α-type error as the usual gamma-pass rate criteria, i.e. when the proportion of detectors with gamma value less than one is greater...
Source: Physics in Medicine and Biology - August 8, 2017 Category: Physics Authors: Ramos Garcia LI, Perez Azorin JF, Aguilar-Redondo PB, Moran-Velasco V Tags: Phys Med Biol Source Type: research
Megahertz rate, volumetric imaging of bubble clouds in sonothrombolysis using a sparse hemispherical receiver array.
Abstract It is well established that high intensity focused ultrasound can be used to disintegrate clots. This approach has the potential to rapidly and noninvasively resolve clot causing occlusions in cardiovascular diseases such as deep vein thrombosis (DVT). However, lack of an appropriate treatment monitoring tool is currently a limiting factor in its widespread adoption. Here we conduct cavitation imaging with a large aperture, sparse hemispherical receiver array during sonothrombolysis with multi-cycle burst exposures (0.1 or 1 ms burst lengths) at 1.51 MHz. It was found that bubble cloud generation on imagi...
Source: Physics in Medicine and Biology - August 8, 2017 Category: Physics Authors: Acconcia CN, Jones RM, Goertz DE, O'Reilly MA, Hynynen K Tags: Phys Med Biol Source Type: research
Techniques for virtual lung nodule insertion: volumetric and morphometric comparison of projection-based and image-based methods for quantitative CT.
Conclusions: This study shows that both projection-based and image-based nodule insertion techniques yield realistic nodule renditions with statistically similar volume and deformation to synthetic nodules. These Techniques could be used to create a database of hybrid CT images containing nodules of known size, location and morphology. . PMID: 28786399 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 8, 2017 Category: Physics Authors: Robins M, Solomon JB, Sahbaee P, Sedlmair M, Choudhury KR, Pezeshk A, Sahiner B, Samei E Tags: Phys Med Biol Source Type: research
Comparison of region-of-interest-averaged and pixel-averaged analysis of DCE-MRI data based on simulations and pre-clinical experiments.
Abstract Differences between region-of-interest (ROI) and pixel-by-pixel analysis of dynamic contrast enhanced (DCE) MRI data were investigated in this study with computer simulations and pre-clinical experiments. ROIs were simulated with 10, 50, 100, 200, 400, and 800 different pixels. For each pixel, a contrast agent concentration as a function of time, C(t), was calculated using the Tofts DCE-MRI model with randomly generated physiological parameters (Ktrans and ve) and the Parker population arterial input function. The average C(t) for each ROI was calculated and then Ktrans and ve for the ROI was extracted. T...
Source: Physics in Medicine and Biology - August 8, 2017 Category: Physics Authors: He D, Zamora MA, Oto A, Karczmar GS, Fan X Tags: Phys Med Biol Source Type: research
Equivalent magnetic vector potential model for low-frequency magnetic exposure assessment.
This study presents a simple and effective approach for modelling the LF magnetic source. The result of this study could simplify the compliance test procedure for assessing an electrical appliance regarding LF magnetic exposure. PMID: 28783037 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 7, 2017 Category: Physics Authors: Diao Y, Sun W, He Y, Leung S, Siu YM Tags: Phys Med Biol Source Type: research
Photon caliper to achieve submillimeter positioning accuracy.
In conclusion, we demonstrated the VPF test can determine the offset between a 2D detector array and the radiation isocenter with submillimeter accuracy. Until now, no method to locate the radiation isocenter using a 2D detector array has been able to achieve such accuracy. PMID: 28783038 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 7, 2017 Category: Physics Authors: Gallagher KJ, Wong J, Zhang J Tags: Phys Med Biol Source Type: research
Fully automatic left ventricular myocardial strain estimation in 2D short-axis tagged magnetic resonance imaging.
ccedil;a JL Abstract Cardiovascular diseases are among the leading causes of death and frequently result in local myocardial dysfunction. Among the numerous imaging modalities available to detect these dysfunctional regions, cardiac deformation imaging through tagged magnetic resonance imaging (t-MRI) has been an attractive approach. Nevertheless, fully automatic analysis of these data sets is still challenging. In this work, we present a fully automatic framework to estimate left ventricular myocardial deformation from t-MRI. This strategy performs automatic myocardial segmentation based on B-spline explicit acti...
Source: Physics in Medicine and Biology - August 7, 2017 Category: Physics Authors: Morais P, Queirós S, Heyde B, Engvall J, 'hooge JD, Vilaça JL Tags: Phys Med Biol Source Type: research
A viscoelastic model for the prediction of transcranial ultrasound propagation: application for the estimation of shear acoustic properties in the human skull.
In this study, we present global attenuation values and functions that correlate apparent density calculated from computed tomography scans to shear speed of sound. For this purpose, we used a model for sound propagation based on the viscoelastic wave equation (VWE) assuming isotropic conditions. The model was validated using a series of measurements with plates of different plastic materials and angles of incidence of 0°, 15° and 50°. The optimal functions for transcranial ultrasound propagation were established using the VWE, scan measurements of transcranial propagation with an angle of incidence of 40° ...
Source: Physics in Medicine and Biology - August 7, 2017 Category: Physics Authors: Pichardo S, Moreno-Hernández C, Andrew Drainville R, Sin V, Curiel L, Hynynen K Tags: Phys Med Biol Source Type: research
Simultaneous 3D MR elastography of the in vivo mouse brain.
Abstract The feasibility of sample interval modulation (SLIM) magnetic resonance elastography (MRE) for the in vivo mouse brain is assessed, and an alternative SLIM-MRE encoding method is introduced. In SLIM-MRE, the phase accumulation for each motion direction is encoded simultaneously by varying either the start time of the motion encoding gradient (MEG), SLIM-phase constant (SLIM-PC), or the initial phase of the MEG, SLIM-phase varying (SLIM-PV). SLIM-PC provides gradient moment nulling, but the mutual gradient shift necessitates increased echo time (TE). SLIM-PV requires no increased TE, but exhibits non-unifo...
Source: Physics in Medicine and Biology - August 4, 2017 Category: Physics Authors: Kearney SP, Majumdar S, Royston TJ, Klatt D Tags: Phys Med Biol Source Type: research
Characterization of breast calcification types using dual energy X-ray method.
Abstract Calcifications are products of mineralization whose presence is usually associated with pathological conditions. The minerals mostly seen in several diseases are calcium oxalate (CaC2O4), calcium carbonate (CaCO3) and hydroxyapatite (HAp). Up to date, there is no in-vivo method that could discriminate between minerals. To this aim, a dual energy X-ray method was developed in the present study. An analytical model was implemented for the determination of the Calcium/Phosphorus mass ratio (mca/mp ). The simulation was carried out using monoenergetic and polyenergetic X-rays and various calcification thickne...
Source: Physics in Medicine and Biology - August 4, 2017 Category: Physics Authors: Martini N, Koukou V, Fountos G, Michail C, Bakas A, Kandarakis IS, Speller RD, Nikiforidis GC Tags: Phys Med Biol Source Type: research
Equivalent (uniform) square field sizes of flattening filter free photon beams.
Abstract Various types of treatment units such as CyberKnife, TomoTherapy and C-arm linear accelerators (LINACs) are operated using flattening filter free (FFF) photon beams. Their reference dosimetry, however, is currently based on codes of practice that provide data which were primarily developed and tested for high-energy photon beams with flattering filter (WFF). The aim of this work was to introduce equivalent uniform square field sizes of FFF beams to serve as a basis of a unified reference dosimetry procedure applicable to all aforementioned FFF machines. For this purpose, in-house determined experime...
Source: Physics in Medicine and Biology - August 3, 2017 Category: Physics Authors: Lechner W, Kuess P, Georg D, Palmans H Tags: Phys Med Biol Source Type: research
Effect of intra-fraction motion on the accumulated dose for free-breathing MR-guided stereotactic body radiation therapy of renal-cell carcinoma.
This study aims to develop a method for calculating the accumulated dose for MRI-guided SBRT of RCC in the presence of intra-fraction respiratory variations and determine the effect of such variations on the deposited dose. For this, RCC SBRT treatments were simulated while the underlying anatomy was moving, based on motion information from three motion models with increasing complexity: 1) STATIC, in which static anatomy was assumed, 2) AVG-RESP, in which 4D-MRI phase-volumes were time-weighted, and 3) PCA, a method that generates 3D volumes with sufficient spatio-temporal resolution to capture respiration and intra-fract...
Source: Physics in Medicine and Biology - August 3, 2017 Category: Physics Authors: Stemkens B, Glitzner M, Kontaxis C, de Senneville BD, Prins FM, Crijns SPM, Kerkmeijer LGW, Lagendijk JJW, Van den Berg CAT, Tijssen RHN Tags: Phys Med Biol Source Type: research
Are rapid changes in brain elasticity possible?
Abstract Elastography of the brain is a topic of clinical and preclinical research, motivated by the potential for viscoelastic measures of the brain to provide sensitive indicators of pathological processes, and to assist in early diagnosis. To date, studies of the normal brain and of those with confirmed neurological disorders have reported a wide range of shear stiffness and shear wave speeds, even within similar categories. A range of factors including the shear wave frequency, and the age of the individual are thought to have a possible influence. However, it may be that short term dynamics within the brain m...
Source: Physics in Medicine and Biology - August 2, 2017 Category: Physics Authors: Parker KJ Tags: Phys Med Biol Source Type: research
Helium ions at the heidelberg ion beam therapy center: comparisons between FLUKA Monte Carlo code predictions and dosimetric measurements.
We present in this work the comparisons and validations of the Monte Carlo FLUKA code against in-depth dosimetric measurements acquired at the Heidelberg Ion Beam Therapy Center (HIT). Depth dose distributions in water with and without ripple filter, lateral profiles at different depths in water and a spread-out Bragg peak were investigated. After experimentally-driven tuning of the less known initial beam characteristics in vacuum (beam lateral size and momentum spread) and simulation parameters (water ionization potential), comparisons of depth dose distributions were performed between simulations and measurements, which...
Source: Physics in Medicine and Biology - August 1, 2017 Category: Physics Authors: Tessonnier T, Mairani A, Brons S, Sala P, Cerutti F, Ferrari A, Haberer T, Debus J, Parodi K Tags: Phys Med Biol Source Type: research
Superiorized algorithm for reconstruction of CT images from sparse-view and limited-angle polyenergetic data.
Abstract Recent work in CT image reconstruction has seen increasing interest in the use of total variation (TV) and related penalties to regularize problems involving reconstruction from undersampled or incomplete data. Superiorization is a recently proposed heuristic which provides an automatic procedure to 'superiorize' an iterative image reconstruction algorithm with respect to a chosen objective function, such as TV. Under certain conditions, the superiorized algorithm is guaranteed to find a solution that is as satisfactory as any found by the original algorithm with respect to satisfying the constraints of t...
Source: Physics in Medicine and Biology - August 1, 2017 Category: Physics Authors: Humphries T, Winn J, Faridani A Tags: Phys Med Biol Source Type: research
High-energy x-ray Talbot-Lau radiography of a human knee.
We report on a radiographic measurement of an ex vivo human knee using a grating-based phase-contrast imaging setup and a medical x-ray tube at a tube voltage of 70 kV. The measurement has been carried out using a Talbot-Lau setup that is suitable to achieve a high visibility in the energy regime of medical imaging. In a medical reading by an experienced trauma surgeon signatures of chondrocalcinosis in the medial meniscus have been identified more evidently using the dark-field image in comparison to the conventional attenuation image. The analysis has been carried out at various dose levels down to 0.14 mGy measur...
Source: Physics in Medicine and Biology - August 1, 2017 Category: Physics Authors: Horn F, Gelse K, Jabari S, Hauke C, Kaeppler S, Ludwig V, Meyer P, Michel T, Mohr J, Pelzer G, Rieger J, Riess C, Seifert M, Anton G Tags: Phys Med Biol Source Type: research
Dosimetric Predictors of Patient-Reported Xerostomia and Dysphagia With Deintensified Chemoradiation Therapy for HPV-Associated Oropharyngeal Squamous Cell Carcinoma.
Abstract PURPOSE/OBJECTIVE(S): To estimate the association between different dose-volume metrics of the salivary glands and pharyngeal constrictors with patient reported severity of xerostomia/dysphagia in the setting of deintensified chemoradiation therapy (CRT). METHODS AND MATERIALS: Forty-five patients were treated on a phase 2 study assessing the efficacy of deintensified CRT for favorable-risk, HPV-associated oropharyngeal squamous cell carcinoma. Patients received 60 Gy intensity modulated radiation therapy with concurrent weekly cisplatin (30 mg/m(2)), and reported the severity of their xero...
Source: Physics in Medicine and Biology - July 20, 2017 Category: Physics Authors: Chera BS, Fried D, Price A, Amdur RJ, Mendenhall W, Lu C, Das S, Sheets N, Marks L, Mavroidis P Tags: Int J Radiat Oncol Biol Phys Source Type: research
Clinical Outcomes of Large Brain Metastases Treated With Neurosurgical Resection and Intraoperative Cesium-131 Brachytherapy: Results of a Prospective Trial.
CONCLUSIONS: Intraoperative (131)Cs brachytherapy is a promising and effective therapy for large brain metastases requiring neurosurgical intervention, which can offer improved local control and lower rates of RN compared with stereotactic radiosurgery to the resection cavity. PMID: 28721889 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - July 20, 2017 Category: Physics Authors: Wernicke AG, Hirschfeld CB, Smith AW, Taube S, Yondorf MZ, Parashar B, Nedialkova L, Kulidzhanov F, Trichter S, Sabbas A, Ramakrishna R, Pannullo S, Schwartz TH Tags: Int J Radiat Oncol Biol Phys Source Type: research
A back-projection algorithm in the presence of an extra attenuating medium: towards EPID dosimetry for the MR-Linac.
In this study we extended our back-projection method to cope with the presence of an extra attenuating medium between the patient and the EPID. Experiments were performed at a conventional linac, using an aluminum mock-up of the MRI scanner housing between the phantom and the EPID. For a 10 cm square field, the attenuation by the mock-up was 72%, while 16% of the remaining EPID signal resulted from scattered radiation. 58 IMRT fields were delivered to a 20 cm slab phantom with and without the mock-up. EPID reconstructed dose distributions were compared to planned dose distributions using the [Formula: see tex...
Source: Physics in Medicine and Biology - July 17, 2017 Category: Physics Authors: Torres-Xirau I, Olaciregui-Ruiz I, Rozendaal RA, González P, Mijnheer BJ, Sonke JJ, van der Heide UA, Mans A Tags: Phys Med Biol Source Type: research
On Moli ère and Fermi-Eyges scattering theories in hadrontherapy.
On Molière and Fermi-Eyges scattering theories in hadrontherapy. Phys Med Biol. 2017 Jul 17;62(15):6290-6303 Authors: Embriaco A, Bellinzona EV, Fontana A, Rotondi A Abstract We consider the evaluation of lateral spread distributions of charged particle beams at therapeutic energies, due to an absorber in the form of a homogeneous slab or of a stack. We show that the Molière theory has the same degree of flexibility as the Fermi-Eyges, but is much more accurate and does not present particular computing difficulties with the energy loss formula we have employed. It is also shown that the ...
Source: Physics in Medicine and Biology - July 17, 2017 Category: Physics Authors: Embriaco A, Bellinzona EV, Fontana A, Rotondi A Tags: Phys Med Biol Source Type: research
A graphical approach to optimizing variable-kernel smoothing parameters for improved deformable registration of CT and cone beam CT images.
Abstract A systematic method is presented for determining optimal parameters in variable-kernel deformable image registration of cone beam CT and CT images, in order to improve accuracy and convergence for potential use in online adaptive radiotherapy. Assessed conditions included the noise constant (symmetric force demons), the kernel reduction rate, the kernel reduction percentage, and the kernel adjustment criteria. Four such parameters were tested in conjunction with reductions of 5, 10, 15, 20, 30, and 40%. Noise constants ranged from 1.0 to 1.9 for pelvic images in ten prostate cancer patients. A total of 51...
Source: Physics in Medicine and Biology - July 17, 2017 Category: Physics Authors: Hart V, Burrow D, Allen Li X Tags: Phys Med Biol Source Type: research
A hybrid phantom Monte Carlo-based method for historical reconstruction of organ doses in patients treated with cobalt-60 for Hodgkin's lymphoma.
In this study, a computational model and experimental validation of the Theratron T-1000 are presented. Model validation is based upon in-field commissioning data collected at the University of Florida, published out-of-field data from the British Journal of Radiology (BJR) Supplement 25, and out-of-field measurements performed at the University of Wisconsin's Accredited Dosimetry Calibration Laboratory (UWADCL). The computational model of the Theratron T-1000 agrees with central axis percentage depth dose data to within 2% for 6 × 6 to 30 × 30 ...
Source: Physics in Medicine and Biology - July 17, 2017 Category: Physics Authors: Petroccia H, Mendenhall N, Liu C, Hammer C, Culberson W, Thar T, Mitchell T, Li Z, Bolch W Tags: Phys Med Biol Source Type: research
New prospective 4D-CT for mitigating the effects of irregular respiratory motion.
Abstract Artifact caused by irregular respiration is a major source of error in 4D-CT imaging. We propose a new prospective 4D-CT to mitigate this source of error without new hardware, software or off-line data-processing on the GE CT scanner. We utilize the cine CT scan in the design of the new prospective 4D-CT. The cine CT scan at each position can be stopped by the operator when an irregular respiration occurs, and resumed when the respiration becomes regular. This process can be repeated at one or multiple scan positions. After the scan, a retrospective reconstruction is initiated on the CT console to reconst...
Source: Physics in Medicine and Biology - July 17, 2017 Category: Physics Authors: Pan T, Martin RM, Luo D Tags: Phys Med Biol Source Type: research
Monte Carlo skin dose simulation in intraoperative radiotherapy of breast cancer using spherical applicators.
In this study, modeling of the X-ray source and related applicators were performed using the Monte Carlo N-Particle (MCNP) transport code. The dosimetric characteristics of the model were validated against measured data obtained using an ionization chamber and EBT3 film as dosimeters. By using a simulated breast phantom, absorbed doses to the skin for different combinations of applicator size (1.5 to 5 cm) and treatment depth (0.5 to 3 cm) were calculated. Simulation results showed overdosing of the skin (> 30% of prescribed dose) at a treatment depth of 0.5 cm using applicator sizes larger than 1.5 cm. Skin doses w...
Source: Physics in Medicine and Biology - July 14, 2017 Category: Physics Authors: Moradi F, Ung NM, Khandaker MU, Mahdiraji GA, Saad M, Abdul Malik R, Bustam AZ, Zaili Z, Bradley DA Tags: Phys Med Biol Source Type: research
DNA double strand break (DSB) induction and cell survival in iodine-enhanced computed tomography (CT).
Abstract A multi-scale Monte Carlo model is proposed to assess the dosimetric and biological impact of iodine-based contrast agents commonly used in computed tomography. As presented, the model integrates the general purpose MCNP6 code system for larger-scale radiation transport and dose assessment with the Monte Carlo damage simulation to determine the sub-cellular characteristics and spatial distribution of initial DNA damage. The repair-misrepair-fixation model is then used to relate DNA double strand break (DSB) induction to reproductive cell death. Comparisons of measured and modeled changes in reproductive c...
Source: Physics in Medicine and Biology - July 13, 2017 Category: Physics Authors: Streitmatter SW, Stewart RD, Jenkins PA, Jevremovic T Tags: Phys Med Biol Source Type: research
Effects of body habitus on internal radiation dose calculations using the 5-year-old anthropomorphic male models.
This study aims to evaluate the influence of body habitus on internal dosimetry and to quantify the uncertainties in dose estimation correlated with the use of fixed reference models. The 5-year-old IT'IS male phantom was modified to match target anthropometric parameters, including body weight, body height and sitting height/stature ratio (SSR), determined from reference databases, thus enabling the creation of 125 5-year-old habitus-dependent male phantoms with 10th, 25th, 50th, 75th and 90th percentile body morphometries. We evaluated the absorbed fractions and the mean absorbed dose to the target region per unit cumula...
Source: Physics in Medicine and Biology - July 13, 2017 Category: Physics Authors: Xie T, Kuster N, Zaidi H Tags: Phys Med Biol Source Type: research
Effect of bone-soft tissue friction on ultrasound axial shear strain elastography.
Abstract Bone-soft tissue friction is an important factor affecting several musculoskeletal disorders, frictional syndromes and the ability of a bone fracture to heal. However, this parameter is difficult to determine using non-invasive imaging modalities, especially in clinical settings. Ultrasound axial shear strain elastography is a non-invasive imaging modality that has been used in the recent past to estimate the bonding between different tissue layers. As most elastography methods, axial shear strain elastography is primarily used in soft tissues. More recently, this technique has been proposed to assess the...
Source: Physics in Medicine and Biology - July 12, 2017 Category: Physics Authors: Tang S, Chaudhry A, Kim N, Reddy JN, Righetti R Tags: Phys Med Biol Source Type: research
Systematic investigation on the validity of partition model dosimetry for < sup > 90 < /sup > Y radioembolization using Monte Carlo simulation.
Conclusions: PM leads to inaccurate dose estimations due to the exclusion of cross-fire irradiation, i.e. between the tumour and normal liver tissue. Caution should be taken for cases with higher TI and T/N, and lower LS, as they contribute to major underestimation of D<sub>NL</sub>. For D<sub>L</sub>, different correction factor for dose calculation may be used for improved accuracy. . PMID: 28686171 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - July 7, 2017 Category: Physics Authors: Hashikin NAA, Yeong CH, Guatelli S, Abdullah BJJ, Ng KH, Malaroda A, Rozenfeld AB, Perkins AC Tags: Phys Med Biol Source Type: research
Ultrasonic computed tomography based on full-waveform inversion for bone quantitative imaging.
Abstract We introduce an ultrasonic quantitative imaging method for long bones based on full-waveform inversion. The cost function is defined as the difference in the L2-norm sense between observed data and synthetic results at a given iteration of the iterative inversion process. For simplicity, and in order to reduce the computational cost, we use a two-dimensional acoustic approximation. The inverse problem is solved iteratively based on a quasi-Newton technique called the Limited-memory Broyden-Fletcher-Goldfarb-Shanno method. We show how the technique can be made to work fine for benchmark models consisting o...
Source: Physics in Medicine and Biology - July 7, 2017 Category: Physics Authors: Bernard S, Monteiller V, Komatitsch D, Lasaygues PL Tags: Phys Med Biol Source Type: research
Online pretreatment verification of high-dose rate brachytherapy using an imaging panel.
This study describes a pre-treatment verification system that uses an imaging panel (IP) to verify important aspects of the treatment plan. A detailed modelling of the IP was only possible with an extensive calibration performed using a robotic arm. Irradiations were performed with a high dose rate (HDR) (192)Ir source within a water phantom. An empirical fit was applied to measure the distance between the source and the detector so 3D Cartesian coordinates of the dwell positions can be obtained using a single panel. The IP acquires 7.14 fps to verify the dwell times, dwell positions and air kerma strength (Sk). A gynecolo...
Source: Physics in Medicine and Biology - June 15, 2017 Category: Physics Authors: Fonseca GP, Podesta M, Bellezzo M, Van den Bosch MR, Lutgens L, Vanneste BGL, Voncken R, Van Limbergen EJ, Reniers B, Verhaegen F Tags: Phys Med Biol Source Type: research
Arterial waveguide model for shear wave elastography: implementation and in vitro validation.
Abstract Arterial stiffness is found to be an early indicator of many cardiovascular diseases. Among various techniques, shear wave elastography has emerged as a promising tool for estimating local arterial stiffness through the observed dispersion of guided waves. In this paper, we develop efficient models for the computational simulation of guided wave dispersion in arterial walls. The models are capable of considering fluid-loaded tubes, immersed in fluid or embedded in a solid, which are encountered in in vitro/ex vivo, and in vivo experiments. The proposed methods are based on judiciously combining Fourier tr...
Source: Physics in Medicine and Biology - June 15, 2017 Category: Physics Authors: Astaneh AV, Urban MW, Aquino W, Greenleaf JF, Guddati MN Tags: Phys Med Biol Source Type: research
A new method to reconstruct intra-fractional prostate motion in volumetric modulated arc therapy.
The objective function penalized the distance from the reconstructed 3D position of each fiducial marker to the corresponding straight line, defined by the x-ray projection of the marker. Rigid translational motion of the prostate and motion smoothness along the temporal dimension were assumed and incorporated into the optimization model. We tested the motion reconstruction method in both simulation and phantom experimental studies. We quantified the accuracy using 3D normalized root-mean-square (RMS) error defined as the norm of a vector containing ratios between the absolute RMS errors and corresponding motion ranges in ...
Source: Physics in Medicine and Biology - June 15, 2017 Category: Physics Authors: Chi Y, Rezaeian NH, Shen C, Zhou Y, Lu W, Yang M, Hannan R, Jia X Tags: Phys Med Biol Source Type: research
A light-weight compact proton gantry design with a novel dose delivery system for broad-energetic laser-accelerated beams.
Abstract Proton beams may provide superior dose-conformity in radiation therapy. However, the large sizes and costs limit the widespread use of proton therapy (PT). The recent progress in proton acceleration via high-power laser systems has made it a compelling alternative to conventional accelerators, as it could potentially reduce the overall size and cost of the PT facilities. However, the laser-accelerated beams exhibit different characteristics than conventionally accelerated beams, i.e. very intense proton bunches with large divergences and broad-energy spectra. For the application of laser-driven beams in P...
Source: Physics in Medicine and Biology - June 15, 2017 Category: Physics Authors: Masood U, Cowan TE, Enghardt W, Hofmann KM, Karsch L, Kroll F, Schramm U, Wilkens JJ, Pawelke J Tags: Phys Med Biol Source Type: research
Prophylactic Cranial Irradiation in Resected Early-Stage Small Cell Lung Cancer.
PMID: 28581402 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - June 8, 2017 Category: Physics Authors: Eze C, Roengvoraphoj O, Manapov F Tags: Int J Radiat Oncol Biol Phys Source Type: research
Iterative image-domain ring artifact removal in cone-beam CT.
Abstract Ring artifacts in cone beam computed tomography (CBCT) images are caused by pixel gain variations using flat-panel detectors, and may lead to structured non-uniformities and deterioration of image quality. The purpose of this study is to propose a method of general ring artifact removal in CBCT images. This method is based on the polar coordinate system, where the ring artifacts manifest as stripe artifacts. Using relative total variation, the CBCT images are first smoothed to generate template images with fewer image details and ring artifacts. By subtracting the template images from the CBCT images, res...
Source: Physics in Medicine and Biology - June 6, 2017 Category: Physics Authors: Liang X, Zhang Z, Niu T, Yu S, Wu S, Li Z, Zhang H, Xie Y Tags: Phys Med Biol Source Type: research
Modelling of induced electric fields based on incompletely known magnetic fields.
Abstract Determining the induced electric fields in the human body is a fundamental problem in bioelectromagnetics that is important for both evaluation of safety of electromagnetic fields and medical applications. However, existing techniques for numerical modelling of induced electric fields require detailed information about the sources of the magnetic field, which may be unknown or difficult to model in realistic scenarios. Here, we show how induced electric fields can accurately be determined in the case that the magnetic fields are known only approximately, e.g., based on field measurements. The robustness o...
Source: Physics in Medicine and Biology - June 6, 2017 Category: Physics Authors: Laakso I, De Santis V, Cruciani S, Campi T, Feliziani M Tags: Phys Med Biol Source Type: research
Application of fluence field modulation to proton computed tomography for proton therapy imaging.
Abstract This simulation study presents the application of fluence field modulated computed tomography (FFMCT), initially developed for x-ray CT, to proton computed tomography (pCT). By using pencil beam (PB) scanning, fluence modulated pCT (FMpCT) may achieve variable image quality in a pCT image and imaging dose reduction. Three virtual phantoms, a uniform cylinder and two patients, were studied using Monte Carlo simulations of an ideal list-mode pCT scanner. Regions of interests (ROI) were selected for high image quality and only PBs intercepting them preserved full fluence (FF). Image quality was investi...
Source: Physics in Medicine and Biology - June 5, 2017 Category: Physics Authors: Dedes G, De Angelis L, Rit S, Hansen D, Belka C, Bashkirov V, Johnson R, Coutrakon G, Schubert K, Landry G, Schulte R, Parodi K Tags: Phys Med Biol Source Type: research
A beam monitoring and validation system for continuous line scanning in proton therapy.
We report on its design and implementation in this paper. In line scanning, we steer the proton beam continuously along straight lines while adapting the speed and/or current frequently to modulate the delivered dose. We intend to prevent delivery errors that could be clinically relevant through a two-stage system: Safety level 1 monitors the beam current and position every 10 μs. We demonstrate that direct readings from ionization chambers in the gantry nozzle and Hall probes in the scanner magnets provide required information on current and position, respectively. Interlocks will be raised when measured sig...
Source: Physics in Medicine and Biology - June 5, 2017 Category: Physics Authors: Klimpki G, Psoroulas S, Bula C, Rechsteiner U, Eichin M, Weber D, Lomax A, Meer D Tags: Phys Med Biol Source Type: research
Detection of anatomical changes in lung cancer patients with 2D time-integrated, 2D time-resolved and 3D time-integrated portal dosimetry: a simulation study.
gen F Abstract The aim of this work is to assess the performance of 2D time-integrated (2D-TI), 2D time-resolved (2D-TR) and 3D time-integrated (3D-TI) portal dosimetry in detecting dose discrepancies between the planned and (simulated) delivered dose caused by simulated changes in the anatomy of lung cancer patients. For six lung cancer patients, tumor shift, tumor regression and pleural effusion are simulated by modifying their CT images. Based on the modified CT images, time-integrated (TI) and time-resolved (TR) portal dose images (PDIs) are simulated and 3D-TI doses are calculated. The modified and orig...
Source: Physics in Medicine and Biology - June 5, 2017 Category: Physics Authors: Wolfs CJA, Brás M, Schyns L, Nijsten S, van Elmpt W, Scheib S, Baltes C, Podesta M, Verhaegen F Tags: Phys Med Biol Source Type: research
Automated diagnosis of prostate cancer in multi-parametric MRI based on multimodal convolutional neural networks.
Abstract Automated methods for prostate cancer (PCa) diagnosis in multi-parametric magnetic resonance images (MP-MRI) are critical for increasing the survival rate of patients and alleviating requirements in radiology reading and reducing risk of over-/under-treatment. This paper presents an automated method based on multimodal convolutional neural networks (CNNs) for two PCa diagnosis tasks: 1) distinguishing between cancer and noncancerous tissues, 2) distinguishing between clinically significant (CS) and indolent PCa. Specifically, our multimodal CNNs effectively fuse apparent diffusion coefficients (ADC) and T...
Source: Physics in Medicine and Biology - June 5, 2017 Category: Physics Authors: Le MH, Chen J, Wang L, Wang Z, Liu W, Cheng KT, Yang X Tags: Phys Med Biol Source Type: research