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Physics in Medicine and Biology

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https://www.readbyqxmd.com/read/28333689/computational-modelling-of-the-cerebral-cortical-microvasculature-effect-of-x-ray-microbeams-versus-broad-beam-irradiation
#1
Andreas Merrem, Stefan Bartzsch, Jean Laissue, Uwe Oelfke
Microbeam Radiation Therapy is an innovative pre-clinical strategy which uses arrays of parallel, tens of micrometre wide kilo-voltage photon beams to treat tumours. These X-ray beams are typically generated on a synchrotron source. It was shown that these beam geometries allow exceptional normal tissue sparing from radiation damage while still being effective in tumour ablation. A final biological explanation for this enhanced therapeutic ratio has still not been found, some experimental data support an important role of the vasculature...
March 23, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28333688/treatment-planning-of-intensity-modulated-composite-particle-therapy-with-dose-and-linear-energy-transfer-optimization
#2
Taku Inaniwa, Nobuyuki Kanematsu, Koji Noda, Tadashi Kamada
The biological effect of charged-particle beams depends on both dose and radiation quality. The radiation quality of charged-particle beams has been most commonly represented by the linear energy transfer (LET) in radiation biology studies. We investigated a new therapeutic technique using two or more ion species in one treatment session, which we call an Intensity Modulated composite PArtiCle Therapy (IMPACT), for optimizing the physical dose and dose-averaged LET distributions in a patient as its proof of principle...
March 23, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28333041/characterization-of-176lu-background-in-lso-based-pet-scanners
#3
Maurizio Conti, Lars Eriksson, Harold Rothfuss, Therese Sjoeholm, David Townsend, Goeran Rosenqvist, Thomas Carlier
LSO and LYSO are today the most common scintillators used in positron emission tomography. Lutetium contains traces of 176Lu, a radioactive isotope that decays - with a cascade of  photons in coincidence. Therefore, Lutetium-based scintillators are characterized by a small natural radiation background. In this paper, we investigate and characterize the 176Lu radiation background via experiments performed on LSO-based PET scanners. LSO background was measured at different energy windows and different time coincidence windows, and by using shields to alter the original spectrum...
March 23, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28333040/rigid-motion-correction-of-dual-opposed-planar-projections-in-single-photon-imaging
#4
Georgios I Angelis, William Ryder, John Gillam, Frederic Boisson, Andre Kyme, Roger Fulton, Steven Meikle, Peter Kench
Awake and/or freely moving small animal single photon emission imaging allows the continuous study of molecules exhibiting slow kinetics without the need to restrain or anaesthetise the animals. Estimating motion free projections in freely moving small animal planar imaging can be considered as a limited angle tomography problem, except that we wish to estimate the 2D planar projections rather than the 3D volume, where the angular sampling in all three axes depends on the rotational motion of the animal. In this study, we hypothesise that the motion corrected planar projections estimated by reconstructing an estimate of the 3D volume using an iterative motion compensating reconstruction algorithm and integrating it along the projection path, will closely match the true, motion-less, planar distribution regardless of the object motion...
March 23, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28327475/free-breathing-black-blood-cine-fast-spin-echo-imaging-for-measuring-abdominal-aortic-wall-distensibility-a-feasibility-study
#5
Jyh-Miin Lin, Andrew Patterson, Tzu-Cheng Chao, Chengcheng Zhu, Hing-Chiu Chang, Jason Mendes, Hsiao-Wen Chung, Jonathan Gillard, Martin Graves
The paper reports a free-breathing black-blood CINE fast-spin echo (FSE) technique for measuring abdominal aortic wall motion. The free-breathing CINE FSE includes the following MR techniques: 1) variable-density sampling with fast iterative reconstruction; 2) inner-volume imaging; and 3) a blood-suppression preparation pulse. The proposed technique was evaluated in eight healthy subjects. The inner-volume imaging significantly reduced the intraluminal artifacts of respiratory motion (p = 0.015). The quantitative measurements were a diameter of 16...
March 22, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28327474/measurement-and-properties-of-dose-area-product-ratio-in-external-small-beam-radiotherapy
#6
Jarkko Tapio Niemelä, Mari Partanen, Jarkko Ojala, Petri Sipilae, Mikko Björkqvist, Mika Kapanen, Jani Keyriläinen
In small-beam radiation therapy (RT) the measurement of beam quality parameter i.e. tissue-phantom ratio or TPR<sub>20,10</sub> with conventional point detector is a challenge. To obtain reliable results, one has to consider potential sources of error, including volume averaging and adjustment of the point detector into the narrow beam. To overcome these challenges, a different type of possible beam quality parameter in small beams was studied, namely the dose-area product ratio or DAPR<sub>20,10</sub>...
March 22, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28327473/simulation-study-of-a-d-shape-pet-scanner-for-improved-sensitivity-and-reduced-cost-in-whole-body-imaging
#7
Abdella M Ahmed, Hideaki Tashima, Taiga Yamaya
Many research efforts are being made to increase the sensitivity and improve the imaging performance of positron emission tomography (PET) scanners. Conventionally, sensitivity can be increased by increasing the number of detector rings in the axial direction (but at high cost) or reduce the diameter of the scanner (with the disadvantages of reducing the space for patients and degrading the spatial resolution due to the parallax error). In this study, we proposed a PET scanner with a truncated ring and an array of detectors that can be arranged in a straight line below the bed...
March 22, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28327471/motion-compensation-in-extremity-cone-beam-ct-using-a-penalized-image-sharpness-criterion
#8
Alejandro Sisniega, Joseph Stayman, John Yorkston, Jeffrey Siewerdsen, Wojciech Zbijewski
Cone-beam CT (CBCT) for musculoskeletal imaging would benefit from a method to reduce the effects of involuntary patient motion. In particular, the continuing improvement in spatial resolution of CBCT may enable tasks such as quantitative assessment of bone microarchitecture (0.1 mm - 0.2 mm detail size), where even subtle, sub-mm motion blur might be detrimental. We propose a purely image based motion compensation method that requires no fiducials, tracking hardware or prior images. A statistical optimization algorithm (CMA-ES) is used to estimate a motion trajectory that optimizes an objective function consisting of an image sharpness criterion augmented by a regularization term that encourages smooth motion trajectories...
March 22, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28327469/total-body-irradiation-with-a-compensator-fabricated-using-a-3d-optical-scanner-and-a-3d-printer
#9
So-Yeon Park, Jung-In Kim, Yoon Ha Joo, Jung Chan Lee, Jong Min Park
We propose bilateral total body irradiation (TBI) utilizing a 3D printer and a 3D optical scanner. We acquired surface information of an anthropomorphic phantom with the 3D scanner and fabricated the 3D compensator with the 3D printer, which could continuously compensate for the lateral missing tissue of an entire body from the beam's eye view. To test the system's performance, we measured doses with optically stimulated luminescent dosimeters (OSLDs) as well as EBT3 films with the anthropomorphic phantom during TBI without a compensator, conventional bilateral TBI, and TBI with the 3D compensator (3D TBI)...
March 22, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28327466/regional-deep-hyperthermia-impact-of-observer-variability-in-ct-based-manual-tissue-segmentation-on-a-simulated-temperature-distribution
#10
Bassim Aklan, Josefin Hartmann, Diana Zink, Hadi Siavooshhaghighi, Ricarda Merten, Florian Putz, Oliver Ott, Rainer Fietkau, Christoph Bert
The aim of this study was to systematically investigate the influence of inter- and intra-observer segmentation variation of tumor and organs at risk on the simulated temperature coverage of the target. CT scans of six patients with tumors in the pelvic region acquired for radiotherapy treatment planning were used for the hyperthermia treatment planning. To study the effect of inter-observer variation, three observers manually segmented in the CT images of each patient the following structures: fat, muscle, bone and bladder...
March 22, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28327464/monte-carlo-simulations-of-time-of-flight-pet-with-double-ended-readout-calibration-coincidence-resolving-times-and-statistical-lower-bounds
#11
Stephen E Derenzo
This paper demonstrates through Monte Carlo simulations that a practical positron emission tomograph with (1) deep scintillators for efficient detection, (2) double-ended readout for depth-of-interaction information, (3) fixed-level analog triggering, and (4) accurate calibration and timing data corrections can achieve a coincidence resolving time (CRT) that is not far above the statistical lower bound. One Monte Carlo algorithm simulates a calibration procedure that uses data from a positron point source. Annihilation events with an interaction near the entrance surface of one scintillator are selected, and data from the two photodetectors on the other scintillator provide depth-dependent timing corrections...
March 22, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28323642/a-bayesian-approach-for-three-dimensional-markerless-tumor-tracking-using-kv-imaging-during-lung-radiotherapy
#12
Chun-Chien Shieh, Vincent Caillet, Michelle Dunbar, Paul J Keall, Jeremy T Booth, Nicholas Hardcastle, Carol Haddad, Thomas Eade, Ilana Feain
The ability to monitor tumor motion without implanted markers can potentially enable broad access to more accurate and precise lung radiotherapy. A major challenge is that kilovoltage (kV) imaging based methods are rarely able to continuously track the tumor due to the inferior tumor visibility on 2D kV images. Another challenge is the estimation of 3D tumor position based on only 2D imaging information. The aim of this work is to address both challenges by proposing a Bayesian approach for markerless tumor tracking for the first time...
March 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28323641/metal-artifacts-in-computed-tomography-for-radiation-therapy-planning-dosimetric-effects-and-impact-of-metal-artifact-reduction
#13
Drosoula Giantsoudi, Bruno De Man, Joost Verburg, Alexei Trofimov, Yannan Jin, Ge Wang, Lars Gjesteby, Harald Paganetti
A significant and increasing number of patients receiving radiation therapy present with metal objects close to, or even within, the treatment area, resulting in artifacts in computed tomography (CT) imaging, which is the most commonly used imaging method for treatment planning in radiation therapy. In the presence of metal implants, such as dental fillings in treatment of head-and-neck tumors, spinal stabilization implants in spinal or paraspinal treatment or hip replacements in prostate cancer treatments, the extreme photon absorption by the metal object leads to prominent image artifacts...
March 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28323638/fast-lesion-mapping-during-hifu-treatment-using-harmonic-motion-imaging-guided-focused-ultrasound-hmigfus-in-vitro-and-in-vivo
#14
Yang Han, Shutao Wang, Thomas Payen, Elisa Konofagou
The successful clinical application of high intensity focused ultrasound (HIFU) ablation depends on reliable monitoring of the lesion formation. Harmonic motion imaging guided focused ultrasound (HMIgFUS) is an ultrasound-based elasticity imaging technique, which monitors HIFU ablation based on the stiffness change of the tissue instead of the echo intensity change in conventional B-mode monitoring, rendering it potentially more sensitive to lesion development. Our group has shown that predicting the lesion location based on the radiation force-excited region is feasible during HMIgFUS...
March 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28323637/accelerated-monte-carlo-simulation-on-the-chemical-stage-in-water-radiolysis-using-gpu
#15
Zhen Tian, Steve B Jiang, Xun Jia
The accurate simulation of water radiolysis is an important step to understand the mechanisms of radiobiology and quantitatively test some hypotheses regarding radiobiological effects. However, the simulation of water radiolysis is highly time consuming, taking hours or even days to be completed by a conventional CPU processor. This time limitation hinders cell-level simulations for a number of research studies. We recently initiated efforts to develop gMicroMC, a GPU-based fast microscopic MC simulation package for water radiolysis...
March 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28323633/rotational-magneto-acousto-electric-tomography-maet-theory-and-experimental-validation
#16
L Kunyansky, C P Ingram, R S Witte
We present a novel two-dimensional (2D) MAET scanner, with a rotating object of interest and two fixed pairs of electrodes. Such an acquisition scheme, with our novel reconstruction techniques, recovers the boundaries of the regions of constant conductivity uniformly well, regardless of their orientation. We also present a general image reconstruction algorithm for the 2D MAET in a circular chamber with point-like electrodes immersed into the saline surrounding the object. An alternative linearized reconstruction procedure is developed, suitable for recovering the material interfaces (boundaries) when a non-ideal piezoelectric transducer is used for acoustic excitation...
March 21, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28319042/smartphone-application-for-mechanical-quality-assurance-of-medical-linear-accelerator
#17
Hwiyoung Kim, Hyunseok Lee, Jong In Park, Chang Heon Choi, So-Yeon Park, Hee Jung Kim, Young Suk Kim, Sung-Joon Ye
Mechanical quality assurance (QA) of medical linear accelerators consists of time consuming and human-error prone procedures. We developed a smartphone-application system for mechanical QA. The system consists of two smartphones; one attached to the gantry to obtain real-time information on mechanical parameters of medical linear accelerator, and the other to display the real-time information by bluetoothing the former. Motion sensors embedded in the smartphone were used to measure gantry and collimator rotations...
March 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28319041/practical-use-of-a-plastic-scintillator-for-quality-assurance-of-electron-beam-therapy
#18
Katsunori Yogo, Yuya Tatsuno, Masato Tsuneda, Yuki Aono, Daiki Mochizuki, Yoshiki Fujisawa, Akihiro Matsushita, Minoru Ishigami, Hiromichi Ishiyama, Kazushige Hayakawa
Quality assurance (QA) of the clinical electron beam is essential for performing accurate and safe radiation therapy. However, with advances in radiation therapy, QA tends to be labor-intensive and time consuming. Here, we propose the practical use of a tissue-equivalent plastic scintillator for quick and easy QA of clinical electron beams. This tool enabled us to verify simultaneously the constancy of output, beam quality, depth and lateral dose profiles during monthly QAs at lower doses of irradiation (small MUs)...
March 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28319031/evaluation-of-the-water-equivalence-of-plastic-materials-in-low-and-high-energy-clinical-proton-beams
#19
Ana Lourenco, David Shipley, Nigel Wellock, Russell Thomas, Hugo Bouchard, Andrzej Kacperek, Francesco Fracchiolla, Stefano Lorentini, Marco Schwarz, Niall MacDougall, Gary Royle, Hugo Palmans
The aim of this work was to evaluate the water-equivalence of new trial plastics designed specifically for light-ion beam dosimetry as well as commercially available plastics in clinical proton beams. The water-equivalence of materials was tested by computing a plastic-to-water conversion factor, <i>H</i><sub><i>pl</i>,w</sub>. Trial materials were characterized experimentally in 60 MeV and 226 MeV un-modulated proton beams and the results were compared with Monte Carlo simulations using the FLUKA code...
March 20, 2017: Physics in Medicine and Biology
https://www.readbyqxmd.com/read/28306557/mri-micturating-urethrography-for-improved-urethral-delineation-in-prostate-radiotherapy-planning-a-case-study
#20
Robba Rai, Mark Sidhom, Karen Lim, Lucy Ohanessian, Gary P Liney
Stereotactic ablative body radiotherapy is used in prostate cancer to deliver a high dose of radiation to the tumour over a small number of treatments. This involves the simulation of the patient using both CT and MRI. Current practice is to insert an indwelling catheter (IDC) during CT to assist with visualisation of the urethra and subsequently minimise dose to this highly critical structure. However, this procedure is invasive and has an associated risk of infection. This is a case study, which demonstrates our initial experience of using a real-time non-invasive MRI technique to replace the use of IDC for prostate cancer patients...
March 17, 2017: Physics in Medicine and Biology
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