The effects of inter-crystal scattering events on the performance of PET detectors.
Abstract The probability of inter-crystal scattering (ICS) events for 511 keV gamma rays in all current scintillation crystals is high and the ICS events degrade the spatial resolution of PET scanners. In this work, Monte Carlo simulations were performed to study the effects of ICS events on the sensitivity and spatial resolution of PET detectors. LaBr3, LYSO, and PWO that representing scintillation crystals of low, medium and high density, respectively, were used. For a point source placed in the middle of two scintillation detectors of 50×50×20 mm3 and a lower energy threshold (LET) of 350 keV, the p...
Source: Physics in Medicine and Biology - September 16, 2019 Category: Physics Authors: Zhang C, Sang Z, Wang X, Zhang X, Yang Y Tags: Phys Med Biol Source Type: research

Measurement of PET isotope production cross sections for protons and carbon ions on carbon and oxygen targets for applications in particle therapy range verification.
Abstract Measured cross sections for the production of the PET isotopes C-10, C-11 and O-15 from carbon and oxygen targets induced by protons (40-220 MeV) and carbon ions (65-430 MeV/u) are presented. These data were obtained via activation measurements of irradiated graphite and beryllium oxide targets using a set of three scintillators coupled by a coincidence logic. The measured cross sections are relevant for the PET particle range verification method where accurate predictions of the β+ emitter distribution produced by therapeutic beams in the patient tissue are required. The presented dataset is useful ...
Source: Physics in Medicine and Biology - September 16, 2019 Category: Physics Authors: Horst F, Adi W, Arico G, Brinkmann KT, Durante M, Reidel CA, Rovituso M, Weber U, Zaunick HG, Zink K, Schuy C Tags: Phys Med Biol Source Type: research

Construction of realistic hybrid computational fetal phantoms from radiological images in three gestational ages for radiation dosimetry applications.
Abstract Radiation exposure and associated radiation risks are major concerns for fetal development for pregnant patients who undergo radiation therapy or diagnostic imaging procedures. In order to accurately estimate the radiation dose to the fetus and assess the uncertainty of fetal position and rotation, three hybrid computational fetus phantoms were constructed using magnetic resonance imaging (MRI) for each fetus model as a starting point to construct a complete anatomically accurate fetus, gravid uterus, and placenta. A total of 27 fetal organs were outlined from radiological images via the Velocity Treatmen...
Source: Physics in Medicine and Biology - September 16, 2019 Category: Physics Authors: Makkia RS, Nelson KH, Zaidi H, Dingfelder M Tags: Phys Med Biol Source Type: research

Fast automated multi-criteria planning for HDR brachytherapy explored for prostate cancer.
Abstract We developed a fast and fully-automated, multi-criteria treatment planning workflow for high dose rate brachytherapy (HDR-BT). In this workflow, the patient-CT with catheter reconstructions and dwell positions are imported from the clinical TPS into a novel system for automated dwell time optimisation. The optimised dwell times are then imported into the clinical TPS. The aims of automation were 1) planner-independent, enhanced plan quality, 2) short optimisation times. Our in-house developed system for fully automated, multi-criteria external beam radiotherapy (EBRT) treatment planning (Erasmus-iCycle) w...
Source: Physics in Medicine and Biology - September 16, 2019 Category: Physics Authors: Breedveld S, Bennan ABA, Aluwini S, Schaart DR, Kolkman-Deurloo IK, Heijmen BJM Tags: Phys Med Biol Source Type: research

A kinetic model of diode detector response to pulsed radiation beams.
Abstract Diodes dosimeters present a complex response to pulsed beams, with diode sensitivity varying with dose-per-pulse, monitor unit rate (time between pulses) or number of integrated pulses. Such response is caused by the complex kinetics of the interplay among charge carriers, recombination-generation centers, which capture excess minority charge carriers and facilitate recombination with a majority charge carrier, and traps with energy levels close to the conduction/valence band, which can trap and release charge carriers. This behavior has been well characterized experimentally, and modeled with phenomenolo...
Source: Physics in Medicine and Biology - September 13, 2019 Category: Physics Authors: Neira S, Brualla-Gonzalez L, Prieto-Pena J, Gomez F, Pardo-Montero J Tags: Phys Med Biol Source Type: research

Impact of uncertainties in range and RBE on small field proton therapy.
Abstract To evaluate the clinical impact of biological uncertainties in small field proton therapy due to the assumption of using a constant relative biological effectiveness (RBE) value of 1.1 (RBE-fixed) compared to a variable RBE (RBE-weighted). In this context the impact of the applied range margin was investigated.
 
 Eight patients with arteriovenous malformation (AVM) treated with proton radiosurgery were selected due to the small target volume. Dose distributions were compared for RBE-weighted and RBE-fixed. The impact of RBE was assessed using Monte Carlo (MC) dose calculations for...
Source: Physics in Medicine and Biology - September 13, 2019 Category: Physics Authors: Marteinsdottir M, Schuemann J, Paganetti H Tags: Phys Med Biol Source Type: research

Improving the modelling of susceptibility-induced spatial distortions in MRI-guided extra-cranial radiotherapy.
Abstract Magnetic-resonance linear-accelerator (MR-LINAC) systems integrating in-room magnetic-resonance-imaging (MRI) guidance are a currently emerging technology. Such systems address the need to provide frequent imaging at optimal soft-tissue contrast for treatment guidance. However, the use of MRI-guidance in radiotherapy should address imaging-related spatial distortions, which may hinder accurate geometrical characterization of the treatment site. Since spatial encoding relies on well-defined magnetic fields, accurate modeling of the magnetic field alterations due to B_0-inhomogeneities, gradient nonlinearit...
Source: Physics in Medicine and Biology - September 13, 2019 Category: Physics Authors: Kroll C, Dietrich O, Bortfeldt J, Paganelli C, Baroni G, Kamp F, Neppl S, Belka C, Parodi K, Opel M, Riboldi M Tags: Phys Med Biol Source Type: research

Gross tumor volume segmentation for head and neck cancer radiotherapy using deep dense multi-modality network.
In conclusion, our proposed multi-modality Dense-Net can enable satisfied GTV segmentation for HNC using multi-modality images and yield superior performance than conventional methods. Our proposed method provides an automatic, fast and consistent solution for GTV segmentation and shows potentials to be generally applied for radiation therapy planning of a variety of cancer (e.g. lung, sarcoma, liver and so on). PMID: 31514173 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - September 12, 2019 Category: Physics Authors: Guo Z, Guo N, Gong K, Zhong S, Li Q Tags: Phys Med Biol Source Type: research

Improved iterative tomographic reconstruction for x-ray imaging with edge-illumination.
Abstract Iterative tomographic reconstruction has been established as a viable alternative for data analysis in phasesensitive x-ray imaging based on the edge-illumination principle. However, previously published approaches did not account for drifts of optical elements during a scan, which can lead to artefacts. Up to now, the strategy
 to reduce these artefacts was to acquire additional intermediate flat field images, which were used to correct the sinograms. Here, we expand the theoretical model to take these effects into account and demonstrate a significant reduction of (ring)-artefacts in the fin...
Source: Physics in Medicine and Biology - September 11, 2019 Category: Physics Authors: Modregger P, Meganck J, Hagen CK, Massimi L, Olivo A, Endrizzi M Tags: Phys Med Biol Source Type: research

Task-driven optimization of the non-spectral mode of photon counting CT for intracranial hemorrhage assessment.
Abstract Non-contrast CT is widely employed as the first-line imaging test to evaluate for intracranial hemorrhage (ICH). Advances in MDCT technology have greatly improved the image quality of non-contrast CT (NCCT) for the detection of established, relatively large, and acute ICHs. Meanwhile, the reliability of MDCT in detecting microbleeds and chronic hemorrhage, and in predicting hemorrhagic transformation needs to be further improved. The purpose of this work was to investigate the potential use of non-spectral photon counting CT (PCCT) to address these challenges in ICH imaging. Towards this goal, the NCCT pr...
Source: Physics in Medicine and Biology - September 11, 2019 Category: Physics Authors: Ji X, Zhang R, Chen GH, Li K Tags: Phys Med Biol Source Type: research

MRI-guided proton therapy planning: accounting for an inline MRI fringe field.
In this study, the impact of realistic inline MRI fringe field on IMPT plan delivery is investigated for a water phantom, liver tumor and prostate cancer differing in target volume, shape, and field configuration using Monte Carlo simulations. A method to correct for the shift of the beam spot positions in the presence of the inline magnetic field is presented. Results show that when not accounting for the effect of the magnetic field on the pencil beam delivery, the spot positions are substantially shifted and the quality of delivered plans is significantly deteriorated leading to dose inhomogeneities and creation of hot ...
Source: Physics in Medicine and Biology - September 11, 2019 Category: Physics Authors: Burigo LN, Oborn BM Tags: Phys Med Biol Source Type: research

Evaluation of UVA emission from X-ray megavoltage-irradiated tissues and phantoms.
In this study, we develop a UVA-imaging technique to quantify relative UVA CL produced by bulk tissues and other phantoms upon clinical X-ray megavoltage irradiation. 
 UVA CL emission (320-400nm) was quantified in tissue samples of porcine and poultry and in two kinds of solid waters (SW): brown (Standard Imaging, Virtual Waters and white (CIRS, Diagnostic Therapy), and in 1% agarose gels variously doped with absorbing dye. Quantification was achieved through cumulative imaging of the samples placed in a dark, light-blocking chamber during irradiation on a Varian 21 EX accelerator. UVA imaging required a speci...
Source: Physics in Medicine and Biology - September 10, 2019 Category: Physics Authors: Jain S, Yoon SW, Zhang X, Adamson J, Floyd S, Oldham M Tags: Phys Med Biol Source Type: research

A very low diffusion Fricke gel dosimeter with functionalised Xylenol orange-PVA (XOPVA).
Abstract A gel dosimeter has been developed utilising a recently reported system for reducing Fe3+ diffusion in a Fricke gel dosimeter which chelates Xylenol orange to the gelling agent poly(vinyl alcohol) (PVA). Formulations were investigated using both gelatin and PVA as the gelling agent, along with the inclusion of glyoxal. The resulting gel had an optical density dose response of 0.0031 Gy-1, an auto-oxidation rate of 0.00023 h-1, and a diffusion rate of 0.132 mm2 h-1 which is a significant improvement over previously reported gelatin based Fricke gel dosimeters. The gel was also shown to be energy and dose-r...
Source: Physics in Medicine and Biology - September 10, 2019 Category: Physics Authors: Smith ST, Boase N, Masters KS, Hosokawa K, Asena A, Crowe SB, Kairn T, Trapp JV Tags: Phys Med Biol Source Type: research

Error detection using an electromagnetic tracking system in multi-catheter breast interstitial brachytherapy.
Abstract The hybrid treatment delivery system (HTDS) has been proposed as a possible option for a quality assurance in the multi-catheter interstitial brachytherapy for breast cancer patients. The system, which consists out of a prototype afterloader with an integrated electromagnetic tracking (EMT) sensor and an EMT system, allows the automatic measurement of implanted catheters.
 
 To test the feasibility of the system for error detection, possible treatment planning errors and treatment delivery errors were simulated. Planning errors such as an incorrect offset value, an incorrect indexe...
Source: Physics in Medicine and Biology - September 10, 2019 Category: Physics Authors: Masitho S, Kallis K, Strnad V, Fietkau R, Bert C Tags: Phys Med Biol Source Type: research

Low-density gel dosimeter for measurement of the electron return effect in an MR-linac.
In this study, a novel low-density gel dosimeter was developed to simulate lung tissue and was used to measure the ERE at the lung-soft tissue interface. Low-density gel dosimeters were developed with Fricke xylenol orange gelatin (FXG) and ferrous oxide xylenol orange (FOX) gels mixed with polystyrene foam beads of various sizes. The gels were characterized based on CT number, MR signal intensity, and uniformity. All low-density gels had CT numbers roughly equivalent to lung tissue. The optimal lung-equivalent gel formulation was determined to be FXG with <1 mm polystyrene beads due to the higher signal intensi...
Source: Physics in Medicine and Biology - September 10, 2019 Category: Physics Authors: McDonald BA, Lee HJ, Ibbott GS Tags: Phys Med Biol Source Type: research

Data for the dosimetry of low- and medium-energy kV x rays.
Abstract Following the publication of the ICRU Report~90 (2016) on key data for measurement standards in radiation dosimetry, where ionometric air-kerma standards for kilovoltage (kV) x-ray beams are estimated to change by up to about 0.5\%, an update of the backscatter factors and water/air ratios of mass energy-absorption coefficients in kV dosimetry protocols was deemed necessary for consistency with the new ICRU key data. In addition, numerical methods and Monte Carlo (MC) systems that did not exist at the time when air-kerma protocols were developed, are currently available.
 
 Calcula...
Source: Physics in Medicine and Biology - September 6, 2019 Category: Physics Authors: Andreo P Tags: Phys Med Biol Source Type: research

Inorganic scintillation detectors for < sup > 192 < /sup > Ir brachytherapy.
Inorganic scintillation detectors for 192Ir brachytherapy. Phys Med Biol. 2019 Sep 06;: Authors: Kertzscher G, Beddar S Abstract Many brachytherapy (BT) errors could be detected with real-time in vivo dosimetry technology. Inorganic scintillation detectors (ISDs) have demonstrated promising capabilities for BT, because some ISD materials can generate scintillation signals large enough that (a) the background signal emitted in the fiber-optic cable (stem signal) is insignificant, and (b) small detector volumes can be used to avoid volume averaging effects in steep dose gradients near BT sources. We inv...
Source: Physics in Medicine and Biology - September 6, 2019 Category: Physics Authors: Kertzscher G, Beddar S Tags: Phys Med Biol Source Type: research

Commissioning and acceptance guide for the GammaPod.
Abstract The GammaPod breast treatment device has been introduced to provide stereotactic radiation therapy to the breast to patients in the prone position. The GammaPod, using a stereotactic coordinate system, dynamically delivers dose to the target by rotating 25 non-overlapping Co-60 beams while the patient's breast is translated continuously in three axes on the couch during delivery. From simulation to treatment, the patient's breast is immobilized using mild negative pressure (150 mm Hg below atmospheric pressure) through a device-specific dual-cup system with stereotactic fiducials. This technology can be u...
Source: Physics in Medicine and Biology - September 5, 2019 Category: Physics Authors: Becker SJ, Sabouri P, Niu Y, Prado K, Chen S, Nichols E, Yi BY Tags: Phys Med Biol Source Type: research

The role of multiple ionization of H < sub > 2 < /sub > O in heavy ion collisions.
The role of multiple ionization of H2O in heavy ion collisions. Phys Med Biol. 2019 Sep 05;: Authors: Bachi N, Otranto S, Otero GS, Olson RE Abstract Collisional ionization processes involving H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O molecules and C&amp;lt;sup&amp;gt;6+&amp;lt;/sup&amp;gt;, O&amp;lt;sup&amp;gt;8+&amp;lt;/sup&amp;gt;, Si&amp;lt;sup&amp;gt;13+&amp;lt;/sup&amp;gt; ions are studied by means of the classical trajectory Monte Carlo method using molecular orbital calculations to define the ionization stages of the water molecu...
Source: Physics in Medicine and Biology - September 5, 2019 Category: Physics Authors: Bachi N, Otranto S, Otero GS, Olson RE Tags: Phys Med Biol Source Type: research

Evaluation of a deep learning-based pelvic synthetic CT generation technique for MRI-based prostate proton treatment planning.
Abstract The purpose of this work is to validate the application of a deep learning-based method for pelvic synthetic CT (sCT) generation that can be used for prostate proton beam therapy treatment planning. We propose to integrate dense block minimization into 3D cycle-consistent generative adversarial networks (cycle GAN) framework to effectively learn the nonlinear mapping between MRI and CT pairs. A cohort of 17 patients with co-registered CT and MR pairs were used to test the deep learning-based sCT generation method by leave-one-out cross-validation. Image quality between the sCT and CT images, gamma analysi...
Source: Physics in Medicine and Biology - September 5, 2019 Category: Physics Authors: Liu Y, Lei Y, Wang Y, Shafai-Erfani G, Wang T, Tian S, Patel P, Jani AB, McDonald M, Curran WJ, Liu T, Zhou J, Yang X Tags: Phys Med Biol Source Type: research

Dense motion propagation from sparse samples.
Abstract There are many applications for which sparse, or partial sampling of&amp;#13; dynamic image data can be used for articulating or estimating motion within the&amp;#13; medical imaging area. In this new work, we propose a generalized framework for&amp;#13; dense motion propagation from sparse samples which represents an example of transfer&amp;#13; learning and manifold alignment, allowing the transfer of knowledge across imaging&amp;#13; sources of different domains which exhibit different features. Many such examples&amp;#13; exist in medical imaging, from mapping 2D ultrasound or ...
Source: Physics in Medicine and Biology - September 5, 2019 Category: Physics Authors: Smith RL, Dasari P, Lindsay C, King MA, Wells K Tags: Phys Med Biol Source Type: research

Trimmer sequencing time minimization during dynamically collimated proton therapy using a colony of cooperating agents.
Abstract The dynamic collimation system (DCS) can be combined with pencil beam scanning proton therapy to deliver highly conformal treatment plans with unique collimation at each energy layer. This energy layer-specific collimation is accomplished through the synchronized motion of four trimmer blades that intercept the proton beam near the target boundary in the beam's eye view. However, the corresponding treatment deliveries come at the cost of additional treatment time since the translational speed of the trimmer is slower than the scanning speed of the proton pencil beam. In an attempt to minimize the addition...
Source: Physics in Medicine and Biology - September 4, 2019 Category: Physics Authors: Smith BR, Hyer DE, Flynn RT, Hill PM, Culberson WS Tags: Phys Med Biol Source Type: research

A column generation heuristic for VMAT planning with adaptive CVaR constraints.
In this study we develop an efficient computational procedure that generates medically acceptable treatment plans for volumetric modulated arc therapy with constant gantry speed. Our proposed method is a column generation heuristic based on a mixed integer linear programming model, where the objective function contains minimization of total monitor unit of the treatment plan and dose-volume requirements are included as conditional value-at-risk constraints. Our heuristic generates a full treatment arc for the restricted master problem and calibrates the right hand side parameters of the conditional value-at-risk constraint...
Source: Physics in Medicine and Biology - September 4, 2019 Category: Physics Authors: Dursun P, Taşkın ZC, Altınel IK, Bilge H, Donmez Kesen N, Okutan M, Oral EN Tags: Phys Med Biol Source Type: research

Single patient convolutional neural networks for real-time MR reconstruction: A proof of concept application in lung tumor segmentation for adaptive radiotherapy.
Conclusions: We have shown that 3D CNNs can be used for real-time on-the-fly dynamic image reconstruction utilizing both spatial and temporal data in this proof of concept study. We evaluated the technique using six retrospectively undersampled lung cancer patient data sets, as well as prospectively undersampled data acquired from a volunteer and motion phantom. The reconstruction speed achieved for our current implementation was 65 ms per image. &amp;#13; &amp;#13. PMID: 31476750 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - September 2, 2019 Category: Physics Authors: Dietz B, Yun J, Yip E, Gabos Z, Fallone BG, Wachowicz K Tags: Phys Med Biol Source Type: research

Towards continuous-to-continuous 3D imaging in the real world.
Abstract Imaging systems are often modeled as continuous-to-discrete mappings that map the object (i.e., a function of continuous variables such as space, time, energy, wavelength, etc.) to a finite set of measurements. When it comes to reconstruction, some discretized version of the object is almost always assumed, leading to a discrete-to-discrete representation of the imaging system. In this paper, we discuss a method for single photon emission computed tomography (SPECT) imaging that avoids discrete representations of the object or the imaging system, thus allowing reconstruction on an arbitrarily fine set of ...
Source: Physics in Medicine and Biology - August 30, 2019 Category: Physics Authors: Caucci L, Liu Z, Jha AK, Han H, Furenlid LR, Barrett HH Tags: Phys Med Biol Source Type: research

Generative adversarial networks (GAN) for compact beam source modelling in Monte Carlo simulations.
Abstract A method is proposed and evaluated to model large and inconvenient phase space files used in Monte Carlo simulations by a compact Generative Adversarial Network (GAN). The GAN is trained based on a phase space dataset to create a neural network, called Generator (G), allowing G to mimic the multidimensional data distribution of the phase space. At the end of the training process, G is stored with about 0.5 million weights, around 10\,MB, instead of few GB of the initial file. Particles are then generated with G to replace the phase space dataset.&amp;#13; &amp;#13; This concept is applied to beam ...
Source: Physics in Medicine and Biology - August 30, 2019 Category: Physics Authors: Sarrut D, Krah N, Letang JM Tags: Phys Med Biol Source Type: research

Integration of dynamic contrast-enhanced magnetic resonance imaging and T2-weighted imaging radiomic features by a canonical correlation analysis-based feature fusion method to predict histological grade in ductal breast carcinoma.
Abstract Tumour histological grade has prognostic implications in breast cancer. Tumour features in dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and T2-weighted (T2W) imaging can provide related and complementary information in the analysis of breast lesions to improve MRI-based histological status prediction in breast cancer. A dataset of 167 patients with invasive ductal carcinoma (IDC) was assembled, consisting of 72 low/intermediate-grade and 95 high-grade cases with preoperative DCE-MRI and T2W images. The data cohort was separated into development (n=111) and validation (n=56) cohorts. Each...
Source: Physics in Medicine and Biology - August 30, 2019 Category: Physics Authors: Fan M, Liu Z, Xie S, Xu M, Wang S, Gao X, Li L Tags: Phys Med Biol Source Type: research

4D Monte Carlo dose calculations for pre-treatment quality assurance of VMAT SBRT: a phantom-based feasibility study.
This study has demonstrated the feasibility of this 4DMC method. PMID: 31470421 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 30, 2019 Category: Physics Authors: Roberts NF, Williams M, Holloway L, Metcalfe P, Oborn BM Tags: Phys Med Biol Source Type: research

Deep-learning assisted automatic digitization of interstitial needles in 3D CT image based high dose-rate brachytherapy of gynecological cancer.
Abstract Digitization of interstitial needles is a complicated and tedious process for the treatment planning of 3D CT image based interstitial high dose-rate brachytherapy (HDRBT) of gynecological cancer. We developed a deep-learning assisted auto-digitization method for interstitial needles. The digitization method consisted of two steps. The first step used a deep neural network with a U-net structure to segment all needles from CT images. The second step simultaneously clustered the segmented voxels into different needle groups and generated the needle central trajectories by solving an optimization problem. W...
Source: Physics in Medicine and Biology - August 30, 2019 Category: Physics Authors: Jung H, Shen C, Gonzalez Y, Albuquerque K, Jia X Tags: Phys Med Biol Source Type: research

Cascaded systems analysis of anatomic noise in digital mammography and dual-energy digital mammography.
Abstract In x-ray based imaging of the breast, contrast between fibroglandular (Fg) tissue and adipose (Ad) tissue is a source of anatomic noise. The goal of this work was to validate by simulation and experiment a mathematical framework for modelling the Fg component of anatomic noise in digital mammograpy (DM) and dual-energy (DE) DM. Our mathematical framework unifies and generalizes existing approaches. We compared mathematical predictions directly with empirical measurements of the anatomic noise power spectrum of the CIRS BR3D structured breast phantom using two clinical mammography systems and four beam qua...
Source: Physics in Medicine and Biology - August 30, 2019 Category: Physics Authors: Tanguay J, Lalonde R, Bjarnason TA, Yang CJ Tags: Phys Med Biol Source Type: research

Breast phantoms for 2D digital mammography with realistic anatomical structures and attenuation characteristics based on clinical images using 3D printing.
In conclusion, an approach to produce anthropomorphic breast phantoms for DM offering realistic anatomical structures and attenuation characteristics based on clinical images was successfully developed. As shown, the phantom realistically simulated the original female breast. Therefore, it is to expect that such phantoms are promising to support bridging the gap between physical-technical and diagnostic image quality assessment. In addition, they enable a variety of practical and scientific applications for which present technical phantoms are not suitable. PMID: 31469105 [PubMed - as supplied by publisher] (Source: P...
Source: Physics in Medicine and Biology - August 29, 2019 Category: Physics Authors: Schopphoven S, Cavael P, Bock K, Fiebich M, Mäder U Tags: Phys Med Biol Source Type: research

Personalized kidney dosimetry in 177Lu-octreotate treatment of neuroendocrine tumours: a comparison of kidney dosimetry estimates based on a whole organ and small volume segmentations.
Abstract Peptide receptor radionuclide therapy (PRRT) with 177Lu- radiolabeled octreotate is an effective treatment method for inoperable neuroendocrine tumours (NETs). There is growing evidence that estimates of the organ-at-risks (OARs) doses are necessary for the optimization of personalized PRRT (P-PRRT). Dosimetry, however, requires a complicated and time-consuming procedure, which hinders its implementation in the clinic. The aim of this study is to develop a practical and automatic technique to simplify personalized dosimetry of kidney, the major OAR in 177Lu P-PRRT. The data from 30 NETs patients undergoin...
Source: Physics in Medicine and Biology - August 28, 2019 Category: Physics Authors: Hou X, Zhao W, Beauregard JM, Celler A Tags: Phys Med Biol Source Type: research

Characterization of dynamic collimation mechanisms for helical CT scans with direct measurements.
Conclusion: &amp;#13; With direct measurements of primary x-ray beam coverage, dynamic collimation mechanisms and related dose reduction effects were characterized for four modern wide-beam CT scanners. PMID: 31461411 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 27, 2019 Category: Physics Authors: Yang K, Li Z, Li X, Liu B Tags: Phys Med Biol Source Type: research

ReconSocket: a low-latency raw data streaming interface for real-time MRI-guided radiotherapy.
Abstract With the recent advent of hybrid MRI-guided radiotherapy systems, continuous intra-fraction MR imaging for motion monitoring has become feasible. The ability to perform real-time custom image reconstructions is however often lacking. In this work we present a low-latency streaming solution, ReconSocket, which provides a real-time stream of k-space data from the MRI to custom reconstruction servers. &amp;#13; &amp;#13; We determined the performance of the data streaming by measuring the streaming latency (i.e., non-zero time delay due to data transfer and processing) and jitter (i.e., deviations fr...
Source: Physics in Medicine and Biology - August 27, 2019 Category: Physics Authors: Borman PTS, Raaymakers BW, Glitzner M Tags: Phys Med Biol Source Type: research

Optimal energy selection for proton stopping-power-ratio estimation using dual-energy CT-based monoenergetic imaging.
In this study, we revisited the idea of coupling the stoichiometric calibration method with virtual monoenergetic CT datasets (MonoCT) generated by modern DECT scanners, because of its readiness for implementation with the existing TPS. Our objective was to determine the optimal energy of the MonoCT dataset for stoichiometric calibration and estimate the overall uncertainty in SPR estimation at the optimal energy. We performed stoichiometric calibration for MonoCT datasets across the energy range available on a Siemens Force DECT scanner and a Philips IQon DECT scanner in a 10 keV step. We estimated the uncertainties of di...
Source: Physics in Medicine and Biology - August 22, 2019 Category: Physics Authors: Je E, Lee HH, Duan X, Li B, Jia X, Yang M Tags: Phys Med Biol Source Type: research

On the conversion from dose-to-medium to dose-to-water in heterogeneous phantoms with Acuros XB and Monte Carlo calculations.
Abstract The method implemented in Monte Carlo (MC) algorithm to convert dose-to-medium (Dm) to dose-to-water (Dw) is usually based on the Bragg-Gray cavity theory. Acuros XB (AXB) reports also Dm and Dw but the method to calculate Dw is based on the energy deposition cross sections for water in place of those for the local media. For both algorithms, the calculation of Dw in non-water media is similar to the dose received in a small volume of water, small enough not to disturb the fluence of charged particles. Recently, two new methods revised the Bragg-Gray cavity theory, one proposed by Andreo and the other by ...
Source: Physics in Medicine and Biology - August 22, 2019 Category: Physics Authors: Delbaere A, Younes T, Vieillevigne L Tags: Phys Med Biol Source Type: research

Gradient regularized convolutional neural networks for low-dose CT image enhancement.
Abstract The potential risks of x-ray to patients have transferred the public's attention from normal dose CT (NDCT) to low-dose CT (LDCT). However, simply lowering the radiation dose of the CT system will significantly degrade the quality of CT images such as noise and artifacts, which compromises the diagnostic performance. Hence, various methods have been proposed to solve this problem over the past decades. Although these methods have achieved impressive results, they also suffer from a drawback of smoothing image details after denoising, which makes it difficult for clinical diagnosis and treatment. To addres...
Source: Physics in Medicine and Biology - August 21, 2019 Category: Physics Authors: Gou S, Liu W, Jiao C, Liu H, Gu Y, Zhang X, Lee J, Jiao L Tags: Phys Med Biol Source Type: research

Polynomial modelling of proton trajectories in homogeneous media for fast most likely path estimation and trajectory simulation.
Abstract Protons undergo many small angle deflections when traversing a medium, such as a patient. This effect, known as multiple Coulomb scattering (MCS), leads to degraded image resolution in proton radiography and computed tomography (CT) and to lateral spreading of the dose distribution in proton therapy. To optimally account for MCS in proton imaging, the most likely path (MLP) of a proton is estimated based on its position and propagation angle measured in front of and behind the object. In this work, we propose a functional which quantifies the likelihood of a proton trajectory and study how it can be used ...
Source: Physics in Medicine and Biology - August 20, 2019 Category: Physics Authors: Krah N, Letang JM, Rit S Tags: Phys Med Biol Source Type: research

Faster PET reconstruction with non-smooth priors by randomization and preconditioning.
CB Abstract Uncompressed clinical data from modern positron emission tomography (PET) scanners are very large, exceeding 350 million data points (projection bins). The last decades have seen tremendous advancements in mathematical imaging tools many of which lead to non-smooth (i.e. non-differentiable) optimization problems which are much harder to solve than smooth optimization problems. Most of these tools have not been translated to clinical PET data, as the state-of-the-art algorithms for non- smooth problems do not scale well to large data. In this work, inspired by big data machine learning applications, we...
Source: Physics in Medicine and Biology - August 20, 2019 Category: Physics Authors: Ehrhardt MJ, Markiewicz PJ, Schönlieb CB Tags: Phys Med Biol Source Type: research

IPEM Topical Report: An evidence and risk assessment based analysis of the efficacy of quality assurance tests on fluoroscopy units - part I; dosimetry and safety.
Abstract This work aims to assess the efficacy of x-ray quality assurance tests undertaken on fluoroscopy units in the UK. Information was gathered on the results of dosimetry and safety tests recommended by the reports of the Institute of Physics and Engineering in Medicine, and those additionally undertaken by medical physics departments. The assessment of efficacy considers the frequency with which a test result breaches the remedial level or other relevant threshold where applicable. The third quartile of those results exceeding the remedial level or threshold is used to estimate the severity of such a breach ...
Source: Physics in Medicine and Biology - August 19, 2019 Category: Physics Authors: Worrall M, Shaw D, Baker C, Charnock P, Fazakerley J, Honey I, Iball GR, Koutalonis M, Price M, Renaud C, Rose A, Wood TJ Tags: Phys Med Biol Source Type: research

A compressed sensing approach to immobilized nanoparticle localization for superparamagnetic relaxometry.
Abstract Superparamagnetic relaxometry (SPMR) exploits the unique magnetic properties of targeted superparamagnetic iron oxide nanoparticles to detect small numbers of cancer cells. Reconstruction of the spatial distribution of cancer-bound nanoparticles requires solving an ill-posed inverse problem. The current method, Multiple Source Analysis (MSA), uses a least-squares fit to determine the strength and location of a pre-determined number of magnetic dipoles. In this proof-of-concept study, we propose the application of a sparsity averaged reweighting algorithm (SARA) for volumetric reconstruction of immobilized...
Source: Physics in Medicine and Biology - August 19, 2019 Category: Physics Authors: Thrower SL, Kandala S, Fuentes D, Stefan W, Sowko NJ, Huang MX, Mathieu KB, Hazle JD Tags: Phys Med Biol Source Type: research

Automatic image-domain Moir é artifact reduction method in grating-based x-ray interferometry imaging.
In this study, we propose to automatically remove Moiré image artifact induced by system instabilities in grating-based x-ray interferometry imaging using convolutional neural network (CNN) technique. This method reduces Moiré image artifact in image-domain via a learned image post-processing procedure, rather than developing signal retrieval optimization algorithms to minimize the inconsistencies between acquired phase stepping data and assumed signal model. To achieve this aim, we train the CNN network using numerical dataset synthesized from both natural images and experimentally acquired Moiré arti...
Source: Physics in Medicine and Biology - August 19, 2019 Category: Physics Authors: Chen J, Zhu J, Li Z, Shi W, Zhang Q, Hu Z, Zheng H, Liang D, Ge Y Tags: Phys Med Biol Source Type: research

Optimizing robot motion for robotic ultrasound-guided radiation therapy.
aefer A Abstract An important aspect of robotic radiation therapy is active compensation of target motion. Recently, ultrasound has been proposed to obtain real-time volumetric images of abdominal organ motion. One approach to realize flexible probe placement throughout the treatment fraction is based on a robotic arm holding the ultrasound probe. However, the probe and the robot holding it may obstruct some of the beams with a potentially adverse effect on the plan quality. This can be mitigated by using a kinematically redundant robot, which allows maintaining a steady pose of the ultrasound probe while moving i...
Source: Physics in Medicine and Biology - August 19, 2019 Category: Physics Authors: Schlüter M, Fürweger C, Schlaefer A Tags: Phys Med Biol Source Type: research

Ensemble of neural networks for 3D position estimation in monolithic PET detectors.
Visvikis D Abstract We propose an ensemble of multilayer feedforward neural networks to estimate the 3D position of photon interactions in monolithic detectors. The ensemble is trained with data generated from optical Monte Carlo simulations only. The originality of our approach is to exploit simulations to obtain reference data, in combination with a variability reduction that the network ensembles offer, thus, removing the need of extensive per-detector calibration measurements. This procedure delivers an ensemble valid for any detector of the same design. We show the capability of the ensemble to solve the 3D ...
Source: Physics in Medicine and Biology - August 15, 2019 Category: Physics Authors: Iborra A, González Martínez AJ, Gonzalez-Montoro A, Bousse A, Visvikis D Tags: Phys Med Biol Source Type: research

Monte Carlo calculation of beam quality correction factors in proton beams using PENH.
pin E Abstract This work calculates beam quality correction factors (&amp;lt;i&amp;gt;k&amp;lt;sub&amp;gt;Q&amp;lt;/sub&amp;gt;&amp;lt;/i&amp;gt;) in both modulated and unmodulated proton beams using the Monte Carlo code PENH. The latest ICRU 90 recommendations on key data for ionizing-radiation dosimetry were adopted to calculate the electronic stopping powers and to select the mean energy to create an ion pair in dry air (&amp;lt;i&amp;gt;W&amp;lt;/i&amp;gt;&amp;lt;sub&amp;gt;air&amp;lt;/sub&amp;gt;). For modulated proton beams, &amp;lt;i&am...
Source: Physics in Medicine and Biology - August 15, 2019 Category: Physics Authors: Gomà C, Sterpin E Tags: Phys Med Biol Source Type: research

Optical simulation study on the spatial resolution of a thick monolithic PET detector.
This study demonstrates the ultimate spatial resolution that can be obtained with this detector without being constrained by practical limitations of experimental setups. In the future these optical simulations may be used as a more precise and fast method to obtain calibration data for real monolithic detectors. PMID: 31416055 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 15, 2019 Category: Physics Authors: Stockhoff M, Van Holen R, Vandenberghe S Tags: Phys Med Biol Source Type: research

An injectable dosimeter for small animal irradiations.
Abstract Accuracy and precision in dosimetry is crucial in studies involving animal models. Small animal dosimetry, in particular for protracted exposures to non uniform radiation fields is particularly challanging. We have developed a novel in-vivo dosimeter based on glass encapsulated TLD rods. These encapsulated rods can be injected into mice and used for validating doses to an individual mouse in a protracted irradiation scenario where the mouse is free to move in an inhomogenous radiation field. Data from 30 irradiated mice shows a reliable dose reconstruction within 10% of the nominal delivered dose. PM...
Source: Physics in Medicine and Biology - August 15, 2019 Category: Physics Authors: Garty G, Pujol-Canadell M, Brenner DJ Tags: Phys Med Biol Source Type: research

Reply to Comment on 'Lateral response heterogeneity of Bragg peak ionization chambers for narrow-beam photon and proton dosimetry'.
Abstract Shen (2019) commented on our paper 'Lateral response heterogeneity of Bragg peak ionization chambers for narrow-beam photon and proton dosimetry' regarding the impact of the low dose tail of the collimated x-ray beam we used to acquire individual response maps of large area ionization chambers. The behavior of this low dose tail was measured and compared to the simulations performed by Shen (2019). It was shown that the model of the tail by Shen (2019) is simplistic and overestimates its effect. PMID: 31416058 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 15, 2019 Category: Physics Authors: Kuess P, Boehlen T, Lechner W, Elia A, Georg D, Palmans H Tags: Phys Med Biol Source Type: research

Comment on 'Lateral response heterogeneity of Bragg peak ionization chambers for narrow-beam photon and proton dosimetry'.
Abstract This comment demonstrated that the low dose tails were not negligible for determining lateral response heterogeneity of Bragg peak ionization chambers. PMID: 31416061 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 15, 2019 Category: Physics Authors: Shen J Tags: Phys Med Biol Source Type: research

Automated 3-D ultrasound image analysis for first trimester assessment of fetal health.
We present a deep learning and image processing solution i) to perform semantic segmentation of the whole fetus, ii) to estimate plane orientation for standard biometry views, iii) to localize and automatically estimate biometry, and iv) to detect fetal limbs from a 3-D first trimester volume. Computational analysis methods were built using a real-world dataset (n=44 volumes). An evaluation on a further independent clinical dataset (n=21 volumes) showed that the automated methods approached human expert assessment of a 3D volume.&amp;#13. PMID: 31408850 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - August 13, 2019 Category: Physics Authors: Ryou H, Yaqub MK, Cavallaro A, Papageorghiou AT, Noble A Tags: Phys Med Biol Source Type: research