13,496 results match your criteria Physics in medicine and biology[Journal]


MR image corrections for PET-induced gradient distortions.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, NRW, GERMANY.

The combination of positron emission tomography (PET) and magnetic resonance imaging (MRI) by using PET inserts in existing MRI scanners is an attractive approach. When designing the PET insert, mutual influences of both imaging modalities need to be minimized. The gradient magnetic fields induce eddy currents in all conductive components of the PET insert. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf97aDOI Listing
December 2018

Predicting tumour response to anti-PD-1 immunotherapy with computational modelling.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

7033 Wisconsin Institute for Medical Research Department of Medical Physics, University of Wisconsin at Madison, Madison, Wisconsin, UNITED STATES.

Cancer immunotherapy is a rapidly developing field, with numerous drugs and therapy combinations waiting to be tested in pre-clinical and clinical settings. However, the costly and time-consuming trial-and-error approach to development of new treatment paradigms creates a research bottleneck, motivating the development of complementary approaches. Computational modelling is a compelling candidate for this task, however, difficulties associated with the validation of such models limits their use in pre-clinical and clinical settings. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf96cDOI Listing
December 2018

Model-based material decomposition with a penalized nonlinear least-squares CT reconstruction algorithm.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

Department of Biomedical Engineering, Johns Hopkins University, 720 Rutland Avenue, Baltimore, Maryland, MD 21205, USA, Baltimore, 21205, UNITED STATES.

Spectral information in CT may be used for material decomposition to produce accurate reconstructions of material density and to separate materials with similar overall attenuation. Traditional methods separate the reconstruction and decomposition steps, often resulting in undesirable trade-offs (e.g. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf973DOI Listing
December 2018

A thermo-sensitive fluorescent agent based method for excitation light leakage rejection for fluorescence molecular tomography.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

Tu and Yuen Center for Functional Onco-Imaging, University of California Irvine, Irvine, California, UNITED STATES.

Fluorescence molecular tomography (FMT) is widely used in preclinical oncology research. FMT is the only imaging technique able to provide three-dimensional distribution of fluorescent probes within thick highly scattering media. However, its integration into clinical medicine has been hampered by its low spatial resolution caused by the undetermined and ill-posed nature of its reconstruction algorithm. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf96dDOI Listing
December 2018

Commissioning of a water calorimeter as a primary standard for absorbed dose to water in magnetic fields.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

Department of Radiotherapy, Universitair Medisch Centrum Utrecht, HP Q.00.118, Heidelberglaan 100, 3584 CX Utrecht, THE NETHERLANDS, Utrecht, NETHERLANDS.

MRI guided radiotherapy devices are currently in clinical use. Detector responses are affected by the magnetic field need to be characterized in terms of absorbed dose to water, <i>D</i><sub>w</sub>, against primary standards under these conditions. The aim of this study was to commission a water calorimeter, accepted as the Dutch national standard for <i>D</i><sub>w</sub> in MV photons and to validate its claimed standard uncertainty of 0. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf975DOI Listing
December 2018

The impact of inter-unit variations on small field dosimetry correction factors, with application to the CyberKnife system.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

medical physics, Sohag University Hospital, Sohag, Egypt, Sohag, EGYPT.

Small field dosimetry correction factors are usually determined from calculations or measurements using one specific example of a treatment system. The sensitivity of the corrections to inter-unit variation is therefore not evaluated. We propose two methods for this evaluation that could be applied to any system. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf971DOI Listing
December 2018

A single detector energy-resolved proton radiography system: a proof of principle study by Monte Carlo simulations.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts, UNITED STATES.

Taking advantage of Bragg peak and small spot size, pencil beam scanning proton therapy can deliver a highly conformal dose distribution to target while sparing normal tissues. However, such dose distributions can be highly sensitive to the proton range uncertainty which can reach 5% or higher in lung tissue. One proposed method for reducing range uncertainty is to measure the water equivalent path length (WEPL) by proton radiography. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf96fDOI Listing
December 2018

TomoTherapy treatments of multiple brain lesions: an in-phantom accuracy evaluation.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

Experimental and Clinical Biomedical Sciences "Mario Serio", Universita di Firenze, Largo Brambilla, 3, Florence, 50134, ITALY.

Purpose: Aim of the present study was to evaluate the accuracy which can be obtained with Helical TomoTherapy ® (HT, Accuray) systems in the case of multiple intracranial targets treatments. Materials and methods: Set-up accuracy was measured, for different registration options and MegaVoltage CT (MVCT) slice thickness, by applying known misalignments to an ad-hoc developed phantom. End-to-End (E2E) tests were performed to assess the delivery accuracy in phantoms containing multiple targets by using radiochromic films: measured dose distribution centroids were compared with physical and calculated target positions on axial and coronal planes. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf977DOI Listing
December 2018

Iterative optimization of relative stopping power by single detector based multi-projection proton radiography.

Phys Med Biol 2018 Dec 18. Epub 2018 Dec 18.

Francis H Burr Proton Therapy Center Department of Radiation Oncology, Massachusetts General Hospital, 30 Fruit Street, Boston, MA 02114, USA, Boston, Massachusetts, UNITED STATES.

In proton therapy, range uncertainties induced by the conversion from x-ray CT (xCT) Hounsfield units (HU) to relative stopping power (RSP) compromise the precision of dose delivery. To reduce range uncertainties induced by HU-converted RSPs, this study investigates optimizing the RSP of individual voxels in xCT iteratively based on multi-projection proton radiography (pRG) acquired using a single amorphous silicon flat panel imager. Time-resolved dose rate functions (DRF) were measured by the imager placed downstream of a test phantom consisting of tissue substitute materials. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf976DOI Listing
December 2018

Accelerating quantitative susceptibility imaging acquisition using compressed sensing.

Phys Med Biol 2018 Dec 10;63(24):245002. Epub 2018 Dec 10.

Department of Radiology, Center for In Vivo Microscopy, Duke University, Durham, NC, United States of America. Department of Radiology, School of Medicine, Duke University, Durham, NC, United States of America.

To evaluate the feasibility of compressed sensing (CS) for accelerating quantitative susceptibility mapping (QSM) acquisition in MR histology, control, demyelination, and remyelination mice were scanned using a modified 3D gradient echo (GRE) pulse sequence (allowing undersampling the k-space in two phase dimensions) at 9.4 T. Fully sampled and CS data at various acceleration factors (AF) (4. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf15dDOI Listing
December 2018
3 Reads

Phase-contrast breast CT: the effect of propagation distance.

Phys Med Biol 2018 Dec 18;63(24):24NT03. Epub 2018 Dec 18.

Department of Physics, University of Trieste, Via A. Valerio 2, 34127 Trieste, Italy. INFN Division of Trieste, Via A. Valerio 2, 34127 Trieste, Italy. Author to whom any correspondence should be addressed.

X-ray phase imaging has the potential to dramatically improve soft tissue contrast sensitivity, which is a crucial requirement in many diagnostic applications such as breast imaging. In this context, a program devoted to perform in vivo phase-contrast synchrotron radiation breast computed tomography is ongoing at the Elettra facility (Trieste, Italy). The used phase-contrast technique is the propagation-based configuration, which requires a spatially coherent source and a sufficient object-to-detector distance. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf2e1DOI Listing
December 2018

Shear wave propagation in viscoelastic media: validation of an approximate forward model.

Phys Med Biol 2018 Dec 3. Epub 2018 Dec 3.

Electrical & Computer Engineering, University of Rochester, Rochester, New York, UNITED STATES.

Many approaches to elastography incorporate shear waves; in some systems these are produced by acoustic radiation force push pulses. Understanding the shape and decay of propagating shear waves in lossy tissues is key to obtaining accurate estimates of tissue properties, and so analytical models have been proposed. In this paper, we reconsider a previous analytical model with the goal of obtaining a computationally straightforward and efficient equation for the propagation of shear waves from a focal push pulse. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf59aDOI Listing
December 2018

Online adaption approaches for intensity modulated proton therapy for head and neck patients based on cone beam CTs and Monte Carlo simulations.

Phys Med Biol 2018 Nov 22. Epub 2018 Nov 22.

Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts, UNITED STATES.

Purpose: To develop an online plan adaptation algorithm for intensity modulated proton therapy (IMPT) based on fast Monte Carlo dose calculation and cone beam CT (CBCT) imaging. Methods: A cohort of 10 head and neck cancer patients with an average of 6 CBCT scans were studied. To adapt the treatment plan to the new patient geometry, contours were propagated to the CBCTs with a vector field (VF) calculated with deformable image registration between the CT and the CBCTs. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf30bDOI Listing
November 2018

Radioluminescence in biomedicine: physics, applications, and models.

Phys Med Biol 2018 Nov 29. Epub 2018 Nov 29.

Radiation Oncology, Stanford University, 300 Pasteur Dr, MC 5132, Grant S277, Stanford, California, 94305, UNITED STATES.

The electromagnetic spectrum contains different frequency bands useful for medical imaging and therapy. Short wavelengths (ionizing radiation) are commonly used for radiological and radionuclide imaging and for cancer radiation therapy. Intermediate wavelengths (optical radiation) are useful for more localized imaging and for photodynamic therapy. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf4deDOI Listing
November 2018

Experimental validation of estimated spatially variant radioisotope-specific point spread functions using published positron range simulations and fluorine-18 measurements.

Phys Med Biol 2018 Dec 7;63(24):24NT01. Epub 2018 Dec 7.

Division of Informatics, Imaging and Data Sciences, MAHSC, University of Manchester, Manchester, United Kingdom. Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, United Kingdom. Author to whom any correspondence should be addressed.

In this work we compare spatially variant radioisotope-specific point spread functions (PSFs) derived from published positron range data with measured data using a high resolution research tomograph (HRRT). Spatially variant PSFs were measured on a HRRT for fluorine-18, carbon-11 and gallium-68 using an array of printed point sources. For gallium-68, this required modification of the original design to handle its longer positron range. Read More

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http://dx.doi.org/10.1088/1361-6560/aaecb6DOI Listing
December 2018

Accurate tooth segmentation with improved hybrid active contour model.

Phys Med Biol 2018 Nov 27. Epub 2018 Nov 27.

Shanghai 9th Peoples Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai, Shanghai, CHINA.

In orthodontic diagnosis and oral treatment planning, 3D tooth model constructed by dental computed tomography (CT) images is an essential and useful assisted tool. In virtue of the higher spatial resolution and lower radiation of X-ray, cone beam computed tomography (CBCT) has been widely used in dental application. However, due to lower signal to noise ratio, vague and weak edge between tooth root and sockets as well as intensity inhomogeneity, the tooth root is easy to be under- segmented and appears false boundary. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf441DOI Listing
November 2018

HIFU-induced changes in optical scattering and absorption of tissue over nine orders of thermal dose.

Phys Med Biol 2018 Dec 7;63(24):245001. Epub 2018 Dec 7.

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom. Author to whom any correspondence should be addressed.

The optical properties of tissue change during thermal ablation. Multi-modal methods such as acousto-optic (AO) and photo-acoustic (PA) imaging may provide a real-time, direct measure of lesion formation. Baseline changes in optical properties have been previously measured over limited ranges of thermal dose for tissues exposed to a temperature-controlled water bath, however, there is scant data for optical properties of lesions created by HIFU. Read More

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http://dx.doi.org/10.1088/1361-6560/aaed69DOI Listing
December 2018

Incorporating automatically learned pulmonary nodule attributes into a convolutional neural network to improve accuracy of benign-malignant nodule classification.

Phys Med Biol 2018 Dec 10;63(24):245004. Epub 2018 Dec 10.

School of Medical Instrument and Food Engineering, University of Shanghai for Science and Technology, Shanghai, People's Republic of China.

Existing deep-learning-based pulmonary nodule classification models usually use images and benign-malignant labels as inputs for training. Image attributes of the nodules, as human-nameable high-level semantic labels, are rarely used to build a convolutional neural network (CNN). In this paper, a new method is proposed to combine the advantages of two classifications, which are pulmonary nodule benign-malignant classification and pulmonary nodule image attributes classification, into a deep learning network to improve the accuracy of pulmonary nodule classification. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf09fDOI Listing
December 2018

Evaluation of the reconstructed dose from the three-dimensional dose module of a helical diode array: factors of influence and error detection.

Phys Med Biol 2018 Nov 28. Epub 2018 Nov 28.

Klinik fur Strahlentherapie, Julius-Maximilians-Universitat Wurzburg, Josef-Schneider-str 11, Würzburg, 97080, GERMANY.

The 3D-dose module (3DVH) of the ArcCHECK-phantom reconstructs the dose distribution in the phantom volume and transfers it to the patient geometry. Our aim was to evaluate the 3DVH-reconstructed dose systematically building up from simple to complex cases. Therefore, the influence of different field sizes without and with blocking the isocenter was tested. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf485DOI Listing
November 2018

Investigation of out-of-plane motion artifacts in 2D noninvasive vascular ultrasound elastography.

Phys Med Biol 2018 Dec 10;63(24):245003. Epub 2018 Dec 10.

Laboratory of Biorheology and Medical Ultrasonics, University of Montreal Hospital Research Center (CRCHUM), Montréal, QC, Canada. Institute of Biomedical Engineering, University of Montreal, Montréal, QC, Canada.

Ultrasound noninvasive vascular elastography (NIVE) has shown its potential to measure strains of carotid arteries to predict plaque instability. When two-dimensional (2D) strain estimation is performed, either in longitudinal or cross-sectional view, only in-plane motions are considered. The motions in elevation direction (i. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf0d3DOI Listing
December 2018
2.761 Impact Factor

Design and testing of a microcontroller that enables alpha particle irradiators to deliver complex dose rate patterns.

Phys Med Biol 2018 Dec 18;63(24):245022. Epub 2018 Dec 18.

Division of Radiation Research, Department of Radiology, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ, United States of America.

There is increasing interest in using alpha particle emitting radionuclides for cancer therapy because of their unique cytotoxic properties which are advantageous for eradicating tumor cells. The high linear energy transfer (LET) of alpha particles produces a correspondingly high density of ionizations along their track. Alpha particle emitting radiopharmaceuticals deposit this energy in tissues over prolonged periods with complex dose rate patterns that depend on the physical half-life of the radionuclide, and the biological uptake and clearance half-times in tumor and normal tissues. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf269DOI Listing
December 2018

Statistical weights for model-based reconstruction in cone-beam CT with electronic noise and dual-gain detector readout.

Phys Med Biol 2018 Dec 14;63(24):245018. Epub 2018 Dec 14.

Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21205, United States of America.

Cone-beam CT (CBCT) systems commonly incorporate a flat-panel detector (FPD) with multiple-gain readout capability to reduce electronic noise and extend dynamic range. In this work, we report a penalized weighted least-squares (PWLS) method for CBCT image reconstruction with a system model that includes the electronic noise characteristics of FPDs, including systems with dynamic-gain or dual-gain (DG) readout in which the electronic noise is spatially varying. Statistical weights in PWLS were modified to account for the contribution of the electronic noise (algorithm denoted [Formula: see text]), and the method was combined with a certainty-based approach that improves the homogeneity of spatial resolution (algorithm denoted [Formula: see text]). Read More

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http://dx.doi.org/10.1088/1361-6560/aaf0b4DOI Listing
December 2018

Design of a spherical applicator for intraoperative radiotherapy with a linear accelerator---a Monte Carlo simulation.

Phys Med Biol 2018 Oct 29. Epub 2018 Oct 29.

Department of Radiation Oncology, Chinese Academy of Medical Sciences and Peking Union Medical College - Cancer Institute and Hospital, PO Box 2258, Beijing 100021, PR CHINA, Beijing, CHINA.

Currently only flat dose distributions can be generated by electron beams of a linear accelerator for intraoperative radiotherapy. However, spherical dose distributions are more desirable for certain types of cancers such as breast cancer and brain cancers. In this study, we propose the design of a spherical applicator for delivery of spherical dose distributions. Read More

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http://dx.doi.org/10.1088/1361-6560/aaec59DOI Listing
October 2018

Monte Carlo study on optimal breast voxel resolution for dosimetry estimates in digital breast tomosynthesis.

Phys Med Biol 2018 Nov 27. Epub 2018 Nov 27.

Radiology and Nuclear Medicine, Radboud University Medical Center, P.O. Box 9101, Route 766, Nijmegen, 6500 HB, NETHERLANDS.

Digital Breast Tomosynthesis (DBT) is currently used as an adjunct technique to Digital Mammography (DM) for breast cancer imaging. Being a quasi-3D image, DBT is capable of providing depth information on the internal breast glandular tissue distribution, which may be enough to obtain an accurate patient-specific radiation dose estimate. However, for this, information regarding the location of the glandular tissue, especially in the vertical direction (i. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf453DOI Listing
November 2018

Y TOF-PET based EUD reunifies patient survival prediction in resin and glass microspheres radioembolization of HCC tumours.

Phys Med Biol 2018 Dec 12;63(24):245010. Epub 2018 Dec 12.

Nuclear Medicine, Saint-Luc Hospital, Brussels, Belgium.

Clinical studies reported a twofold ratio between the efficacies per Gy of resin versus glass spheres. Our aim is to investigate whether this difference could result from the different degrees of heterogeneity in sphere distribution between the two medical devices. The Y TOF-PET based equivalent uniform doses (EUD) was used for this purpose. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf205DOI Listing
December 2018

MRI-based attenuation correction for brain PET/MRI based on anatomic signature and machine learning.

Phys Med Biol 2018 Dec 4. Epub 2018 Dec 4.

Radiology and Imaging Sciences, Emory University, Atlanta, Georgia, UNITED STATES.

Deriving accurate attenuation maps for PET/MRI remains a challenging problem because MRI voxel intensities are not related to properties of photon attenuation and bone/air interfaces have similarly low signal. This work presents a learning-based method to derive patient-specific computed tomography (CT) maps from routine T1-weighted MRI in their native space for attenuation correction of brain PET. We developed a machine-learning-based method using a sequence of alternating random forests under the framework of an iterative refinement model. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf5e0DOI Listing
December 2018

Dose reconstruction from PET images in carbon ion therapy: a deconvolution approach.

Phys Med Biol 2018 Dec 5. Epub 2018 Dec 5.

Experimental Physics Medical Physics, Ludwig-Maximilians-Universitaet Muenchen, Am Coulombwall 1, 85748 Garching b Munchen, Munich, GERMANY.

Dose and range verification have become important tools to bring carbon ion therapy to a higher level of confidence in clinical applications. Positron emission tomography is among the most commonly used approaches for this purpose and relies on the creation of positron emitting nuclei in nuclear interactions of the primary ions with tissue. Predictions of these positron emitter distributions are usually obtained from time-consuming Monte Carlo simulations or measurements from previous treatment fractions, and their comparison to the current, measured image allows for treatment verification. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf676DOI Listing
December 2018

Nasopharyngeal carcinoma segmentation based on enhanced convolutional neural networks using multi-modal metric learning.

Phys Med Biol 2018 Dec 4. Epub 2018 Dec 4.

College of Computer Science, Sichuan University, Chengdu, CHINA.

multi-modality examinations have been extensively applied in current clinical cancer management. Leveraging multi-modality medical images can be highly beneficial for automated tumor segmentation as they provide complementary information that could make the segmentation of tumors more accurate. This paper investigates CNN-based methods for automated nasopharyngeal carcinoma (NPC) segmentation using Computed Tomography (CT) and Magnetic Resonance (MR) images. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf5daDOI Listing
December 2018

Association of pre-treatment radiomic features with lung cancer recurrence following stereotactic body radiation therapy.

Phys Med Biol 2018 Dec 3. Epub 2018 Dec 3.

Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, UNITED STATES.

Purpose: To investigate the potential relationship between radiomic features extracted from pre-treatment CT images and clinical outcomes following stereotactic body radiation therapy (SBRT) for non- small-cell lung cancer (NSCLC). Methods: Seventy patients who received SBRT for stage-1 NSCLC were retrospectively identified. The tumor was contoured on pre-treatment free-breathing CT images, from which 43 quantitative radiomic features were extracted to collectively capture tumor morphology, intensity, fine-texture, and coarse-texture. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf5a5DOI Listing
December 2018

Calculation of absorbed dose in radiotherapy by solution of the linear Boltzmann transport equations.

Authors:
James L Bedford

Phys Med Biol 2018 Nov 14. Epub 2018 Nov 14.

Joint Department of Physics Institute of Cancer Research, Royal Marsden Hospital, Downs Road, Sutton, Surrey, SM2 5PT, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND.

Over the last decade, dose calculations which solve the linear Boltzmann transport equations have been introduced into clinical practice and are now in widespread use. However, knowledge in the radiotherapy community concerning the details of their function is limited. This review gives a general description of the linear Boltzmann transport equations as applied to calculation of absorbed dose in clinical radiotherapy. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf0e2DOI Listing
November 2018

LET dependent response of GafChromic films investigated with MeV ion beams.

Authors:
V Grilj D J Brenner

Phys Med Biol 2018 Dec 18;63(24):245021. Epub 2018 Dec 18.

Author to whom any correspondence should be addressed.

The change in optical properties of GafChromic films depends not only on the absorbed dose, but also on the linear energy transfer (LET) of the ionizing radiation. The influence of LET on the film dose-response relationship is especially important when films are applied for dosimetry of energetic charged particles. In the present study, we examined the response of the unlaminated EBT3 and MD-V3 films to proton, deuterium and helium beams with energies in the range of several megaelectronvolts (MeV). Read More

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http://dx.doi.org/10.1088/1361-6560/aaf34aDOI Listing
December 2018

Determination of kQ factors for cylindrical and plane-parallel ionization chambers in a scanned carbon ion beam by means of cross calibration.

Phys Med Biol 2018 Dec 3. Epub 2018 Dec 3.

Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch - Technische Bundesanstalt, Braunschweig, GERMANY.

The accuracy in the dosimetry of therapeutically used carbon beams is predominantly affected by the large uncertainty of the so-called kQ factor of the ionization chamber used for the measurements. Due to a lack of experimental data, the kQ factor of ionization chambers in carbon beams is still derived by calculation, and, for instance, a standard uncertainty of about 3% is given for kQ factors tabulated in the TRS-398 dosimetric protocol. Recently, kQ factors for two Farmer-type ionization chambers have been determined experimentally in the entrance channel of 429 MeV/u carbon ions, achieving about a threefold reduction of the uncertainty. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf5acDOI Listing
December 2018

Achieving reliable coincidence resolving time measurement of PET detectors using multichannel waveform digitizer based on DRS4 chip.

Phys Med Biol 2018 Dec 10;63(24):24NT02. Epub 2018 Dec 10.

Department of Biomedical Sciences, Seoul National University College of Medicine, Seoul 03080, Republic of Korea. Department of Nuclear Medicine, Seoul National University College of Medicine, Seoul 03080, Republic of Korea.

Coincidence resolving time (CRT) is one of the most important physical-performance measures for positron emission tomography (PET), as reconstruction with accurate time-of-flight information enhances the lesion detectability in patient studies. Accordingly, various PET detector designs and high-performance front-end readout circuits have been actively investigated to improve timing performance. The resulting PET detectors are often evaluated using multichannel waveform digitizers for versatile data analysis of the output signals. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf0bbDOI Listing
December 2018

Comparing Unet training with three different datasets to correct CBCT images for prostate radiotherapy dose calculations.

Phys Med Biol 2018 Nov 28. Epub 2018 Nov 28.

Department of Medical Physics and Department of Radiation Therapy, Ludwig-Maximilians-University, Am Coulombwall 1, Garching, Bavaria, 85748, GERMANY.

Image intensity correction is crucial to enable cone beam computed tomography (CBCT) based radiotherapy dose calculations. This study evaluated three different deep learning based correction methods using a U-shaped convolutional neural network architecture (Unet) in terms of their photon and proton dose calculation accuracy. CT and CBCT imaging data of 42 prostate cancer patients were included. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf496DOI Listing
November 2018

Joint activity and attenuation estimation for PET with TOF data and single events.

Phys Med Biol 2018 Dec 14;63(24):245017. Epub 2018 Dec 14.

UIH America, Inc., Houston, TX, United States of America.

Maximum likelihood reconstruction of activity and attenuation (MLAA) for PET data with time-of-flight (TOF) information can determine the activity distribution up to a scale, and the attenuation map Radon transform up to a related constant. Prior knowledge is widely used for the determination of the constant. However, prior knowledge could be inaccurate due to patient variation and may result in quantitation errors. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf0bcDOI Listing
December 2018

IPEM Topical Report: an evidence and risk assessment based analysis of the efficacy of tube and generator quality assurance tests on general x-ray units.

Phys Med Biol 2018 Dec 12;63(24):245011. Epub 2018 Dec 12.

Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom.

This work aims to assess the efficacy of current x-ray quality assurance (QA) testing regimes on tube and generator systems for general radiographic usage in the UK. 1393 sets of QA results data from nine UK medical physics departments were collected and analysed. Test failure rates ranged from 0% to 39% and were used to assess the likelihood of the test finding a fault. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf112DOI Listing
December 2018

A closer look at ultrasonic attenuation and heating in a tissue-mimicking material.

Phys Med Biol 2018 Dec 10;63(24):245008. Epub 2018 Dec 10.

U.S. Food and Drug Administration, Center for Devices and Radiological Health, 10903 New Hampshire Ave., Silver Spring, MD 20993, United States of America.

A well-characterized ultrasound tissue-mimicking material (TMM) can be important in determining the acoustic output and temperature rise from high intensity therapeutic ultrasound (HITU) devices and also in validating computer simulation models. A HITU TMM previously developed and characterized in our laboratory has been used in our acoustic and temperature measurements as well as modeled in our HITU simulation program. A discrepancy between thermal measurement and simulation, though, led us to further investigate the TMM properties. Read More

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http://dx.doi.org/10.1088/1361-6560/aaec3eDOI Listing
December 2018

A respiratory-guided 4D digital tomosynthesis.

Phys Med Biol 2018 Dec 10;63(24):245007. Epub 2018 Dec 10.

Department of Biomedical Engineering and Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea. Program of Medical Physics and Engineering, Department of Biomedicine and Health Sciences, Graduate School, The Catholic University of Korea, Seoul, Republic of Korea.

The aim of this research was to introduce and evaluate a respiratory-guided slow gantry rotation 4D digital tomosynthesis (DTS). For each of ten volunteers, two breathing patterns were obtained for 3 min, one under free breathing conditions and the other with visual respiratory-guidance using an in-house developed respiratory monitoring system based on pressure sensing. Visual guidance was performed using a 4 s cycle sine wave with an amplitude corresponding to the average of end-inhalation peaks and end-exhalation valleys from the free-breathing pattern. Read More

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http://dx.doi.org/10.1088/1361-6560/aaeddbDOI Listing
December 2018

Fully automated organ segmentation in male pelvic CT images.

Phys Med Biol 2018 Dec 14;63(24):245015. Epub 2018 Dec 14.

Department of Radiation Oncology, Medical Artificial Intelligence and Automation Laboratory, University of Texas Southwestern, Dallas, TX, United States of America. Co-first authors.

Accurate segmentation of prostate and surrounding organs at risk is important for prostate cancer radiotherapy treatment planning. We present a fully automated workflow for male pelvic CT image segmentation using deep learning. The architecture consists of a 2D organ volume localization network followed by a 3D segmentation network for volumetric segmentation of prostate, bladder, rectum, and femoral heads. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf11cDOI Listing
December 2018

Deep-learning based surface region selection for deep inspiration breath hold (DIBH) monitoring in left breast cancer radiotherapy.

Phys Med Biol 2018 Dec 12;63(24):245013. Epub 2018 Dec 12.

School of Biomedical Engineering, Southern Medical University, Guangzhou, Guangdong 510515, People's Republic of China. Department of Radiation Oncology, The University of Texas Southwestern Medical Center, Dallas, TX 75390, United States of America.

Deep inspiration breath hold (DIBH) with surface supervising is a common technique for cardiac dose reduction in left breast cancer radiotherapy. Surface supervision accuracy relies on the characteristics of surface region. In this study, a convolutional neural network (CNN) based automatic region-of-interest (ROI) selection method was proposed to select an optimal surface ROI for DIBH surface monitoring. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf0d6DOI Listing
December 2018

Tumor co-segmentation in PET/CT using multi-modality fully convolutional neural network.

Phys Med Biol 2018 Nov 27. Epub 2018 Nov 27.

School of Automation, Huazhong University of Science and Technology, Wuhan, CHINA.

Automatic tumor segmentation from medical images is an important step for computer-aided cancer diagnosis and treatment. Recently, deep learning has been successfully applied to this task, leading to state-of-the-art performance. However, most of existing deep learning segmentation methods only work for a single imaging modality. Read More

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http://iopscience.iop.org/article/10.1088/1361-6560/aaf44b
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http://dx.doi.org/10.1088/1361-6560/aaf44bDOI Listing
November 2018
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Monte Carlo-based SPECT reconstruction within the SIMIND framework.

Phys Med Biol 2018 Dec 12;63(24):245012. Epub 2018 Dec 12.

Department of Medical Radiation Physics, Lund University, Lund, Sweden. Author to whom any correspondence should be addressed.

This paper presents the development and validation of a Monte Carlo-based singe photon emission computed tomography reconstruction program for parallel-hole collimation contained within the SIMIND Monte Carlo framework. The Monte Carlo code is used as an accurate forward-projector and is combined with a simplified back-projector to perform iterative tomographic reconstruction using the Maximum Likelihood Expectation Maximization and Ordered Subsets Expectation Maximization algorithms, together forming a program called SIMREC. The Monte Carlo simulation transforms the estimated source distribution directly from activity to counts in its projections. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf0f1DOI Listing
December 2018

Noninvasive vascular occlusion with HIFU for venous insufficiency treatment: preclinical feasibility experience in rabbits.

Phys Med Biol 2018 Dec 3. Epub 2018 Dec 3.

INSERM U979, Institut Langevin, Paris, FRANCE.

Venous insufficiency is a common disease arising when veins of the lower limb become incompetent. A conventional surgical strategy consists in stripping the incompetent veins. However, this treatment option is invasive and carries complication risks. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf58dDOI Listing
December 2018

Body motion during dynamic couch tracking with healthy volunteers.

Phys Med Biol 2018 Dec 19;64(1):015001. Epub 2018 Dec 19.

Product Development Group Zurich, Department of Mechanical and Process Engineering, ETH Zurich, Zurich 8092, Switzerland. Department of Radiation Oncology, University Hospital Zurich, Zurich 8091, Switzerland.

In precision radiotherapy, the intrafractional motion can cause a considerable uncertainty of the location of the tumor to be treated. An established approach is the expansion of the target volume to account for the motion. An alternative approach is couch-tracking, in which the patient is continually moved to compensate the intrafractional motion. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf361DOI Listing
December 2018

A new method for modelling the tongue-and-groove in treatment planning systems.

Phys Med Biol 2018 Dec 10;63(24):245005. Epub 2018 Dec 10.

Department of Medical Physics, Hospital Sant Joan de Reus, IISPV, 43204 Tarragona, Spain.

Commercial TPSs typically model the tongue-and-groove (TG) by extending the projections of the leaf sides by a certain constant width. However, this model may produce discrepancies of as much as 7%-10% in the calculated average doses, especially for the High Definition multi-leaf collimator (MLC) (Hernandez et al 2017 Phys. Med. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf098DOI Listing
December 2018

Robust optimization to reduce the impact of biological effect variation from physical uncertainties in intensity-modulated proton therapy.

Phys Med Biol 2018 Dec 4. Epub 2018 Dec 4.

Radiation Physics, MD Anderson Cancer Center, Houston, UNITED STATES.

Purpose: Robust optimization (RO) methods are applied to intensity-modulated proton therapy (IMPT) treatment plans to ensure their robustness in the face of treatment delivery uncertainties, such as proton range and patient setup errors. However, the impact of those uncertainties on the biological effect of protons has not been specifically considered. In this study, we added biological effect-based objectives into a conventional RO cost function for IMPT optimization to minimize the variation in biological effect. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf5e9DOI Listing
December 2018

Contour scanning, multi-leaf collimation and the combination thereof for proton pencil beam scanning.

Phys Med Biol 2018 Nov 22. Epub 2018 Nov 22.

Center for Proton Therapy, Paul Scherrer Institute, WMSA/C12, Villigen - PSI, 5232, SWITZERLAND.

In proton therapy, the lateral fall-off is often used to spare critical organs. It is therefore crucial to improve the penumbra for proton pencil beam scanning. However, previous work has shown that collimation may not be necessary for depths of >15cm in water. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf2e8DOI Listing
November 2018

A depth-of-interaction encoding PET detector module with dual-ended readout using large-area silicon photomultiplier arrays.

Phys Med Biol 2018 Dec 14;63(24):245019. Epub 2018 Dec 14.

Department of Biomedical Engineering, University of California-Davis, One Shields Avenue, Davis, CA 95616, United States of America.

The performance of a depth-of-interaction (DOI) encoding PET detector module with dual-ended readout of LYSO scintillator arrays using large-area SiPM arrays was evaluated. Each SiPM array, with a surface area of 50.2  ×  50. Read More

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http://dx.doi.org/10.1088/1361-6560/aaee32DOI Listing
December 2018

Cascaded systems analysis of a-Se/a-Si and a-InGaZnO TFT passive and active pixel sensors for tomosynthesis.

Phys Med Biol 2018 Dec 4. Epub 2018 Dec 4.

College of Engineering, University of Michigan, Ann Arbor, Michigan, UNITED STATES.

Medical imaging systems like full field digital mammography (FFDM) and digital breast tomosynthesis (DBT) commonly use amorphous selenium (a-Se) based passive pixel sensor (PPS) direct conversion x-ray detectors. On one hand, direct conversion detectors inherently offer better resolution characteristics in terms of a higher modulation transfer function (MTF), in comparison to the indirect CsI:Tl PPS x-ray imager. On the other hand, especially at lower doses, this superior performance of the direct imager is seldom retained in its detective quantum efficiency (DQE) curves. Read More

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http://dx.doi.org/10.1088/1361-6560/aaf5f6DOI Listing
December 2018

Energy-modulated X-ray fluorescence and luminescence emissions from therapeutic nanoparticles.

Phys Med Biol 2018 Nov 6. Epub 2018 Nov 6.

Department of Nuclear, Plasma and Radiological Engineering, University of Illinois - Urbana-Champaign, 214 Nuclear Engineering Laboratory, 103 South Goodwin Avenue, Urbana IL 61801-2984, USA, Urbana, Illinois, UNITED STATES.

In this study, we have investigated the possibility of modulating X-ray fluorescence (XF) and X-ray luminescence (XL) emissions from therapeutic nanoparticles (NPs) by fine-tuning the energy of incident X-rays from benchtop X-ray sources. We have carried out detailed experimental studies to determine the strength of XF and XL emissions from Y2O3:Eu3+ and LaF3:Tb3+ NPs being irradiated with X-rays from benchtop X-ray sources operated with different tube-voltages and coupled to various filter configurations. These studies demonstrated that low-energy X-rays with average energy at around 10-15 keV are the most efficient to stimulate XL emission from the Y2O3:Eu3+ and LaF3:Tb3+ NPs. Read More

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http://dx.doi.org/10.1088/1361-6560/aaeec3DOI Listing
November 2018