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Physics in Medicine and Biology

Nadia Falzone, Boon Lee, José Fernández-Varea, Christiana Kartsonaki, Andrew Stuchbery, Tibor Kibedi, Katherine Vallis
AIM: The aim of this study was to investigate the impact of decay data provided by the newly developed stochastic atomic relaxation model <i>BrIccEmis</i> on dose point kernels (DPKs- radial dose distribution around a unit point source) and <i>S</i>-values (absorbed dose per unit cumulated activity) of 14 Auger electron (AE) emitting radionuclides, namely <sup>67</sup>Ga, <sup>80m</sup>Br, <sup>89</sup>Zr, <sup>90</sup>Nb, <sup>99m</sup>Tc, <sup>111</sup>In, <sup>117m</sup>Sn, <sup>119</sup>Sb, <sup>123</sup>I, <sup>124</sup>I, <sup>125</sup>I, <sup>135</sup>La, <sup>195m</sup>Pt and <sup>201</sup>Tl...
January 19, 2017: Physics in Medicine and Biology
Alan Miranda, Steven Staelens, Sigrid Stroobants, Jeroen Verhaeghe
Preclinical positron emission tomography (PET) imaging in small animals is generally performed under anesthesia to immobilize the animal during scanning. More recently, for rat brain PET studies, methods to perform scans of unrestrained awake rats are being developed in order to avoid the unwanted effects of anesthesia on the brain response. Here, we investigate the use of a projected structure stereo camera to track the motion of the rat head during the PET scan. The motion information is then used to correct the PET data...
January 19, 2017: Physics in Medicine and Biology
Kyung-Wook Jee, Rongxiao Zhang, El Bentefour, Paul Doolan, Ethan Cascio, Gregory Sharp, Jacob Flanz, Hsiao-Ming Lu
Proton beam therapy benefits from the Bragg peak and delivers highly conformal dose distributions. However, the location of the end-of-range is subject to uncertainties related to the accuracy of the relative proton stopping power estimates and thereby the water-equivalent path length (WEPL) along the beam. To remedy the range uncertainty, an in vivo measurement of the WEPL through the patient, i.e. a proton-range radiograph, is highly desirable. Towards that goal, we have explored a novel method of proton radiography based on the time-resolved dose measured by a flat panel imager (FPI)...
January 18, 2017: Physics in Medicine and Biology
Guen Bae Ko, Jae Sung Lee
We propose a novel single transmission-line readout method for whole-body time-of-flight positron emission tomography applications, without compromising on performance. The basic idea of the proposed multiplexing method is the addition of a specially prepared tag signal ahead of the scintillation pulse. The tag signal is a square pulse that encodes photon arrival time and channel information. The two-dimensional position of a silicon photomultiplier (SiPM) array is encoded by the specific width and height of the tag signal...
January 18, 2017: Physics in Medicine and Biology
Sen Wang, Li Zhang, Dufan Wu, Xiaofei Xu
Photon counting detectors can obtain the spectral information of incident x-ray spectrum while the detected counts may differ from the incident counts due to detector response. If uncorrected or uncompensated, the response will lead to distortion in CT reconstruction. With the intention of reducing the distortion and exploring the potential of photon counting detectors, a novel reconstruction strategy with spectral deconvolution is proposed in this paper which attempts to set itself apart from traditional material decomposition framework...
January 18, 2017: Physics in Medicine and Biology
Elira Maksuti, Fabiano Bini, Stefano Fiorentini, Giulia Blasi, Matthew Urban, Franco Marinozzi, Matilda Larsson
Quantitative, non-invasive and local measurements of arterial mechanical properties could be highly beneficial for early diagnosis of cardiovascular disease and follow up of treatment. Arterial Shear Wave Elastography (SWE) and wave velocity dispersion analysis have previously been applied to measure arterial stiffness. Arterial wall thickness (h) and inner diameter (D) vary with age and pathology and may influence the shear wave propagation. Nevertheless, the effect of arterial geometry in SWE has not yet been systematically investigated...
January 12, 2017: Physics in Medicine and Biology
Ho Lee, Benjamin Fahimian, Lei Xing
This paper proposes a binary moving-blocker (BMB)-based technique for scatter correction in cone-beam computed tomography (CBCT). In concept, a beam blocker consisting of lead strips, mounted in front of the x-ray tube, moves rapidly in and out of the beam during a single gantry rotation. The projections are acquired in alternating phases of blocked and unblocked cone beams, where the blocked phase results in a stripe pattern in the width direction. To derive the scatter map from the blocked projections, one-dimensional B-Spline interpolation/extrapolation is applied by using the detected information in the shaded regions...
January 12, 2017: Physics in Medicine and Biology
Xin Ming, Yuanming Feng, Ransheng Liu, Chengwen Yang, Li Zhou, Hezheng Zhai, Jun Deng
The goal of this study is to present a generalized source model (GSM) for accurate Monte Carlo dose simulations of CT scans based solely on the measurement data without a priori knowledge of scanner specifications. The proposed generalized source model consists of an extended circular source located at x-ray target level with its energy spectrum, source distribution and fluence distribution derived from a set of measurement data conveniently available in the clinic. Specifically, the central axis percent depth dose (PDD) curves measured in water and the cone output factors measured in air were used to derive the energy spectrum and the source distribution respectively with a Levenberg-Marquardt algorithm...
January 12, 2017: Physics in Medicine and Biology
Peter M McCowan, Ganiyu Asuni, Timothy van Beek, Eric Van Uytven, Kaden Kujanpaa, Boyd McCurdy
This study reports the development and validation of the first model-based, 3D patient dose reconstruction method for pre-treatment quality assurance using EPID images. The method is also investigated for sensitivity to potential MLC delivery errors. Each cine-mode EPID image acquired during plan delivery was processed using a previously developed back-projection dose reconstruction model providing a 3D dose estimate on the CT simulation data. Validation was carried out using 24 SBRT-VMAT patient plans by comparing: 1) ion chamber point dose measurements in a solid water phantom, 2) the treatment planning system (TPS) predicted 3D dose to the EPID reconstructed 3D dose in a solid water phantom, and 3) the TPS predicted 3D dose to the EPID and our forward predicted reconstructed 3D dose in the patient (CT data)...
January 12, 2017: Physics in Medicine and Biology
Feifei Zhao, Ling Tong, Qiong He, Jianwen Luo
Diverging wave (DW) based cardiac imaging has gained increasing interest in recent years given its capacity to achieve ultrahigh frame rate. However, the signal-to-noise ratio (SNR), contrast, and penetration depth of the resulting B-mode images are typically low as DWs spread energy over a large region. Coded excitation is known to be capable of increasing the SNR and penetration for ultrasound imaging. The aim of this study was therefore to test the feasibility of applying coded excitation in DW imaging to improve the corresponding SNR, contrast and penetration depth...
January 11, 2017: Physics in Medicine and Biology
Charles-Antoine Collins-Fekete, Lennart Volz, Stephen Portillo, Luc Beaulieu, Joao Seco
In this work, a generic rigorous Bayesian formalism is introduced to predict the most likely path of any ion crossing a medium between two detection points. The path is predicted based on a combination of the particle scattering in the material and measurements of its initial and final position, direction and energy. The path estimate's precision is compared to the Monte Carlo simulated path. Every ion from hydrogen to carbon is simulated in two scenarios, 1) where the range is fixed and 2) where the initial velocity is fixed...
January 11, 2017: Physics in Medicine and Biology
Suman Shrestha, Srinivasan Vedantham, Andrew Karellas
In digital breast tomosynthesis and digital mammography, the x-ray beam filter material and thickness vary between systems. Replacing K-edge filters with Al was investigated with the intent to reduce exposure duration and to simplify system design. Tungsten target x-ray spectra were simulated with K-edge filters (50��m Rh; 50��m Ag) and Al filters of varying thickness. Monte Carlo simulations were conducted to quantify the x-ray scatter from various filters alone, scatter-to-primary ratio (SPR) with compressed breasts, and to determine the radiation dose to the breast...
January 11, 2017: Physics in Medicine and Biology
Arvind Balasubramanian, Rittika Shamsuddin, Balakrishnan Prabhakaran, Amit Sawant
Baseline shifts in respiratory patterns can result in significant spatiotemporal changes in patient anatomy (compared to that captured during simulation), in turn, causing geometric and dosimetric errors in the administration of thoracic and abdominal radiotherapy. We propose predictive modeling of the tumor motion trajectories for predicting a baseline shift ahead of its occurrence. The key idea is to use the features of the tumor motion trajectory over a 1-minute window, and predict the occurrence of a baseline shift in the 5 seconds that immediately follow (lookahead window)...
January 11, 2017: Physics in Medicine and Biology
Yu Wang, Bo Peng, Jingfeng Jiang
Ultrasound-based elastography techniques including quasi-static strain elastography (SE), acoustic radiation force Impulse (ARFI) imaging, point shear wave elastography (pSWE) and supersonic shear imaging (SSI) have been used to differentiate breast tumors. The objective of this study is to extend a previously published virtual simulation platform of SE toward acoustic radiation force-based breast elastography. The proposed platform inherited four key components from the previously published virtual SE platform: an ultrasound simulator (Field II), a mesh generator (Tetgen), a finite element (FE) solver (FEBio) and a visualization and data processing package (VTK)...
January 11, 2017: Physics in Medicine and Biology
Takehiro Shiinoki, Hideki Hanazawa, Yuki Yuasa, Koya Fujimoto, Takuya Uehara, Keiko Shibuya
<u>Purposes:</u> A combined system comprising the TrueBeam linear accelerator and a new real-time tumour-tracking radiotherapy system, SyncTraX, was installed at our institution. The objectives of this study are to develop a method for the verification of respiratory-gated radiotherapy with SyncTraX using cine electronic portal image device (EPID) images and a log file and to verify this treatment in clinical cases. <u>Methods and Materials:</u> Respiratory-gated radiotherapy was performed using TrueBeam and the SyncTraX system...
January 10, 2017: Physics in Medicine and Biology
L Cockmartin, N W Marshall, G Zhang, K Lemmens, E Shaheen, C Van Ongeval, E Fredenberg, D R Dance, E Salvagnini, K Michielsen, H Bosmans
This paper introduces and applies a structured phantom with inserted target objects for the comparison of detection performance of digital breast tomosynthesis (DBT) against 2D full field digital mammography (FFDM). The phantom consists of a 48 mm thick breast-shaped polymethyl methacrylate (PMMA) container filled with water and PMMA spheres of different diameters. Three-dimensionally (3D) printed spiculated masses (diameter range: 3.8-9.7 mm) and non-spiculated masses (1.6-6.2 mm) along with microcalcifications (90-250 µm) were inserted as targets...
January 10, 2017: Physics in Medicine and Biology
Pengpeng Zhang, Andreas Rimner, Ellen Yorke, Yu-Chi Hu, Licheng Kuo, Aditya Apte, Natalie Lockney, Andrew Jackson, Gig Mageras, Joseph O Deasy
To develop a geometric atlas that can predict tumor shrinkage and guide treatment planning for non-small-cell lung cancer. To evaluate the impact of the shrinkage atlas on the ability of tumor dose escalation. The creation of a geometric atlas included twelve patients with lung cancer who underwent both planning CT and weekly CBCT for radiotherapy planning and delivery. The shrinkage pattern from the original pretreatment to the residual posttreatment tumor was modeled using a principal component analysis, and used for predicting the spatial distribution of the residual tumor...
January 10, 2017: Physics in Medicine and Biology
James Paul Agnew, Frank O'Grady, Ryan Young, Simon Duane, Geoff Budgell
Integrated magnetic resonance imaging and radiotherapy delivery machines are currently being developed, with some already in clinical use. It is anticipated that the strong magnetic field used in some MR-RT designs will have a significant impact on routine measurements of dose in the MR-linac performed using ionization chambers, which provide traceability back to a primary standard definition of dose. In particular, the presence of small air gaps around ionization chambers may introduce unacceptably high uncertainty into these measurements...
January 10, 2017: Physics in Medicine and Biology
Hualiang Zhong, Salim Siddiqui, Benjamin Movsas, Indrin Chetty
The purpose of this study was to develop metrics to evaluate uncertainties in deformable dose accumulation (DDA) for patients with non-small cell lung cancer (NSCLC). Initial treatment plans (primary) and cone-beam CT (CBCT) images were retrospectively processed for seven NSCLC patients, who showed significant tumor regression during the course of treatment. Each plan was developed with IMRT for 2 Gy��33 fractions. A B-spline-based DIR algorithm was used to register weekly CBCT images to a reference image acquired at fraction 21 and the resultant displacement vector fields (DVFs) were then modified using a finite element method (FEM)...
January 10, 2017: Physics in Medicine and Biology
Chumin Zhao, Nikita Vassiljev, Anastasios Konstantinidis, Robert Speller, Jerzy Kanicki
High-resolution, low-noise x-ray detectors based on the complementary metal-oxide-semiconductor (CMOS) active pixel sensor (APS) technology have been developed and proposed for digital breast tomosynthesis (DBT). In this study, we evaluated the three-dimensional (3D) imaging performance of a 50 ��m pixel pitch CMOS APS x-ray detector named DynAMITe (Dynamic Range Adjustable for Medical Imaging Technology). The two-dimensional (2D) angle-dependent modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) were experimentally characterized and modeled using the cascaded system analysis at oblique incident angles up to 30��...
January 10, 2017: Physics in Medicine and Biology
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