Stochastic frontier analysis as knowledge-based model to improve sparing of organs-at-risk for VMAT-treated prostate cancer.
Abstract Stochastic frontier analysis is used as a novel knowledge-based technique in order to develop a predictive model of dosimetric features from signicant geometric parameters describing a patient morphology. 406 patients treated with VMAT for prostate cancer were analyzed retrospectively. Cases were divided into three prescription-based groups. Seven geometric parameters are extracted to characterize the relationship between the organs-at-risk (bladder and rectum) with the planning volume (PTV). In total, 37 dosimetric parameters are tested for these two OARs. Stochastic frontier analysis allows the determin...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Kroshko A, Morin O, Archambault L Tags: Phys Med Biol Source Type: research

Development of multi-purpose 3D printed phantoms for MRI.
Abstract This work describes the development and application of 3D printed MRI phantoms. Unlike traditional phantoms these test objects are made from solid materials which can be imaged directly without filling. The models were manufactured using both MRI visible and invisible materials. The MRI visible materials were imaged on a 3T system to quantify their T1 and T2 properties and CT to quantify the electron density. Three phantoms are described: A distortion phantom was imaged on an open bore MRI system to assess distortion over a 30 cm field-of-view; A solid tumour model was imaged using a motion simulator and ...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Rai R, Wang YF, Manton D, Dong B, Deshpande S, Liney GP Tags: Phys Med Biol Source Type: research

Automatic PET cervical tumor segmentation by combining deep learning and anatomic prior.
Abstract Cervical tumor segmentation on 3D <sup>18</sup>FDG PET images is a challenging task because of the proximity between cervix and bladder, both of which can uptake <sup>18</sup>FDG tracers. This problem makes traditional segmentation based on intensity variation methods ineffective and reduces overall accuracy. Based on anatomy knowledge, including "roundness" of the cervical tumor and relative positioning between the bladder and cervix, we propose a supervised machine learning method that integrates convolutional neural network (CNN) with th...
Source: Physics in Medicine and Biology - February 28, 2019 Category: Physics Authors: Chen L, Shen C, Zhou Z, Maquilan G, Albuquerque K, Folkert MR, Wang J Tags: Phys Med Biol Source Type: research

Comment on 'Linear energy transfer incorporated intensity modulated proton therapy optimization'.
Abstract Cao et al (2018) published an article on inverse planning based on dose-averaged linear energy transfer (LET). Their claim that the problem can be cast as a linear optimization model relies on an incorrect application of the Charnes-Cooper transformation. In this comment we show that their linear model is simlar to one where dose-averaged LET is multiplied with dose, explaining why their model was nonetheless able to improve the LET distribution. PMID: 30811348 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 27, 2019 Category: Physics Authors: Gorissen BL Tags: Phys Med Biol Source Type: research

Reply to Comment on 'Linear energy transfer incorporated intensity modulated proton therapy optimization'.
Abstract In this reply we present additional description of our linear model for LET optimization in response to the comments by Dr Gorissen. We clarify that this model cannot guarantee global optimal solutions to the sum-of-fractions problem. Based on our data, it could be used to optimize LET efficiently while dose constraints are maintained. PMID: 30811349 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 27, 2019 Category: Physics Authors: Cao W, Khabazian A, Yepes P, Lim G, Poenisch F, Grosshans D, Mohan R Tags: Phys Med Biol Source Type: research

BrachyView: initial preclinical results for a real-time in-body HDR PBT source tracking system with simultaneous TRUS image fusion.
Abstract A prototype in-body gamma camera system with integrated trans-rectal ultrasound (TRUS) and associated real-time image acquisition and analysis software was developed for intraoperative source tracking in high dose rate (HDR) brachytherapy. The accuracy and temporal resolution of the system was validated experimentally using a deformable tissue-equivalent prostate gel phantom and a full clinical HDR treatment plan. The BrachyView system was able to measure 78% of the 200 source positions with an accuracy of better than 1 mm. A minimum acquisition time of 0.28 s/frame was required to achieve this accuracy, ...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Alnaghy S, Cutajar DL, Safavi-Naeini M, George S, Howie A, Bece A, Bucci JA, Jakubek J, Pospisil S, Lerch MLF, Petasecca M, Rozenfeld AB Tags: Phys Med Biol Source Type: research

Dosimetric accuracy of dynamic couch rotation during volumetric modulated arc therapy (DCR-VMAT) for primary brain tumours.
Abstract Radiotherapy treatment plans using dynamic couch rotation during volumetric modulated arc therapy (DCR-VMAT) reduce the dose to organs at risk (OARs) compared to coplanar VMAT, while maintaining the dose to the planning target volume (PTV). This paper seeks to validate this finding with measurements. DCR-VMAT treatment plans were produced for five patients with primary brain tumours and delivered using a commercial linear accelerator (linac). Dosimetric accuracy was assessed using point dose and radiochromic film measurements. Linac- recorded mechanical errors were assessed by extracting deviations from l...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Smyth G, Evans PM, Bamber JC, Mandeville HC, Moore AR, Welsh LC, Saran FH, Bedford JL Tags: Phys Med Biol Source Type: research

Monte Carlo simulations of out-of-field surface doses due to the electron streaming effect in orthogonal magnetic fields.
Abstract The out-of-field surface dose contribution due to backscattered or ejected electrons, contained by the magnetic field, is evaluated in this work. This electron streaming effect (ESE) can contribute to out-of-field skin doses and toxicity in orthogonal magnetic resonance guided radiation therapy machines. Using the EGSnrc Monte Carlo package, a central phantom is set-up with an incident 10X10cm<sup>2</sup> 7MV FFF photon beam. The phantom exit or entry surface is inclined with respect to the magnetic field, and an out-of-field water panel is positioned 10cm away from...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Malkov VN, Hackett SL, Wolthaus JWH, Raaymakers BW, van Asselen B Tags: Phys Med Biol Source Type: research

Uniqueness of poroelastic and viscoelastic nonlinear inversion MR elastography at low frequencies.
Abstract Intrinsic actuation MR Elastography (IA-MRE) exploits natural pulsations of the brain as a motion source to estimate mechanical property maps. The low frequency motion of IA-MRE introduces new considerations for inversion algorithms relative to traditional external actuation MRE. Specifically, inertial forces become very small, which leaves low frequency viscoelastic inversions with a non-unique scalar multiplier. Biphasic poroelastic inversions include additional fluid-solid interaction forces to balance the elastic forces, which avoids the non-uniqueness. Analyzing the convergence behavior from differen...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: McGarry MDJ, Van Houten E, Solamen L, Gordon-Wylie S, Weaver J, Paulsen KD Tags: Phys Med Biol Source Type: research

A segmentation method combining probability map and boundary based on multiple fully convolution network and repetitive training.
Abstract Cell nuclei image segmentation technology can help researchers observe each cell's stress response to drug treatment. However, it is still a challenge to accurately segment the adherent cell nuclei. At present, image segmentation based on fully convolutional network (FCN) is attracting researcher's attention. We propose a Multiple FCN architecture and Repetitive Training (M-FCN-RT) method to learn features of cell nucleus images. In M-FCN-RT, the Multiple FCN (M-FCN) architecture is composed of several Single FCNs (S-FCN) with the same structure, and each FCN is used to learn the specific features of imag...
Source: Physics in Medicine and Biology - February 26, 2019 Category: Physics Authors: Yin W, Hu Y, Yi S, He J Tags: Phys Med Biol Source Type: research

Impact of TPS calculation algorithms on dose delivered to the patient in proton therapy treatments.
Conclusion: Different TPS dose calculation approaches mainly affected dose delivered in H&N proton treatments, while minor deviations were found for pelvic tumors. RS-MC proved to be the most accurate TPS dose calculation algorithm when compared to an independent MC simulation code. PMID: 30802887 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 25, 2019 Category: Physics Authors: Molinelli S, Russo S, Magro G, Maestri D, Mairani A, Mastella E, Mirandola A, Vai A, Vischioni B, Valvo F, Ciocca M Tags: Phys Med Biol Source Type: research

Fiducial marker based intra-fraction motion assessment on cine-MR for MR-Linac treatment of prostate cancer.
Conclusion We have developed a robust, fast and accurate FM tracking algorithm for cine-MR data, which allows for continuous monitoring of prostate motion during MR-guided radiotherapy (MRgRT). These results will be used to validate automatic prostate tracking based on soft-tissue contrast. PMID: 30794995 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 22, 2019 Category: Physics Authors: de Muinck Keizer DM, Pathmanathan AU, Andreychenko A, Kerkmeijer LGW, van der Voort van Zyp JRN, Tree AC, Van den Berg CAT, de Boer JCJ Tags: Phys Med Biol Source Type: research

Posture-dependent dose coefficients of mesh-type ICRP reference computational phantoms for photon external exposures.
Abstract Recently, the International Commission on Radiological Protection (ICRP) developed new mesh-type reference computational phantoms (MRCPs) that provide high deformability compared with the current voxel-type reference computational phantoms of ICRP Publication 110. Taking advantage of this deformability, in the present study, the MRCPs were deformed to five non-standing postures (i.e., walking, sitting, bending, kneeling, and squatting) by developing and using a systematic posture-change method based on the as-rigid-as-possible (ARAP) shape-deformation algorithm and motion-capture technology. The non-stand...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Yeom YS, Han H, Choi C, Nguyen TT, Shin B, Lee C, Kim CH Tags: Phys Med Biol Source Type: research

Computational modelling of resistance and associated treatment response heterogeneity in metastatic cancers.
Abstract Metastatic cancer patients invariably develop treatment resistance. Different levels of resistance lead to observed heterogeneity in treatment response. The main goal was to evaluate treatment response heterogeneity with computation model simulating dynamics of drug-sensitive and drug-resistant cells. Model parameters included proliferation, drug induced death, transition and proportion of intrinsically resistant cells. Model was benchmarked with imaging metric extracted from 39 metastatic prostate cancer patients who had 18F-NaF-PET/CT scans performed at baseline and three cycles into chemotherapy or hor...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Turk M, Simoncic U, Roth A, Valentinuzzi D, Jeraj R Tags: Phys Med Biol Source Type: research

Integrating DVH criteria into a column generation algorithm for VMAT treatment planning.
Abstract Volumetric-modulated arc therapy (VMAT) treatment planning is an efficient treatment technique with a high degree of flexibility in terms of dose rate, gantry speed, and aperture shapes during rotation around the patient. However, the dynamic nature of VMAT results in a large-scale nonconvex optimization problem. Determining the priority of the tissues and voxels to obtain clinically acceptable treatment plans poses additional challenges for VMAT optimization. The main purpose of this paper is to develop an automatic planning approach integrating dose-volume histogram (DVH) criteria in direct aperture opt...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Mahnam M, Gendreau M, Lahrichi N, Rousseau LM Tags: Phys Med Biol Source Type: research

Oblique raster scanning: an ion dose delivery procedure with variable energy layers.
Abstract In ion Therapy Accelerator Complexes the dose is delivered "actively" by subdividing the target in Equal Energy Layers, which are scanned by a beam spot visiting in sequence the planned spots, previously defined by the Treatment Planning System. Synchrotrons-based complexes have three problems: (i) the switching from the energy needed to scan one Equal Energy Layer to the next takes time, an effect that is more relevant for the very short treatment times now often required; (ii) the unavoidable "ripples" of the quadrupoles and bending magnets currents produce large erratic time variati...
Source: Physics in Medicine and Biology - February 21, 2019 Category: Physics Authors: Amaldi U Tags: Phys Med Biol Source Type: research

A cone-shaped gradient coil design for high-resolution MRI head imaging.
Abstract Insertable head gradient coils offer significant advantages such as high gradient strength and fast gradient switching speed owing to close distance to the target region of interest than whole-body cylindrical coils. To produce superior gradient performance, the local head coil is typically designed with an asymmetric configuration to accommodate both the shoulders and head of a patient, leading to tough dimensional constraints and practical limits to the coil implementation. In this paper, we proposed a new cone-shaped model to improve the performance of the asymmetric head coils and also to mitigate pat...
Source: Physics in Medicine and Biology - February 19, 2019 Category: Physics Authors: Tang F, Hao J, Freschi F, Niu C, Repetto M, Liu F, Crozier S Tags: Phys Med Biol Source Type: research

Combining many-objective radiomics and 3-dimensional convolutional neural network through evidential reasoning to predict lymph node metastasis in head and neck cancer.
Abstract Lymph node metastasis (LNM) is a significant prognostic factor in patients with head and neck cancer, and the ability to predict it accurately is essential to optimizing treatment. Positron emission tomography (PET) and computed tomography (CT) imaging are routinely used to identify LNM. Although large or highly active lymph nodes (LNs) have a high probability of being positive, identifying small or less reactive LNs is challenging. The accuracy of LNM identification strongly depends on the physician's experience, so an automatic prediction model for LNM based on CT and PET images is warranted to assist L...
Source: Physics in Medicine and Biology - February 19, 2019 Category: Physics Authors: Chen L, Zhou Z, Sher D, Zhang Q, Shah J, Pham NL, Jiang SB, Wang J Tags: Phys Med Biol Source Type: research

McSART: an iterative model-based, motion-compensated SART algorithm for CBCT reconstruction.
Abstract 4D cone beam computed tomography (CBCT) images of the thorax and abdomen can have reduced quality due to the limited number of projections per respiratory bin used in gated image reconstruction. In this work, we present a new algorithm to reconstruct high quality CBCT images by simultaneously reconstructing images and generating an associated respiratory motion model. This is done by updating model parameters to compensate for motion during the iterative image reconstruction process. CBCT image acquisition was simulated using the digital eXternal CArdiac Torso (XCAT) phantom, simulating breathing motion u...
Source: Physics in Medicine and Biology - February 18, 2019 Category: Physics Authors: Chee G, O'Connell D, Yang Y, Singhrao K, Low DA, Lewis JH Tags: Phys Med Biol Source Type: research

A mixed-integer linear programming optimization model framework for capturing expert planning style in low dose rate prostate brachytherapy.
Abstract Low dose rate (LDR) brachytherapy is a minimally invasive form of radiation therapy, used to treat prostate cancer, and it involves permanent implantation of radioactive sources (seeds) inside of the prostate gland. Treatment planning in brachytherapy involves a decision making process for the placement of the sources in order to deliver an effective dose of radiation to cancerous tissue in the prostate while sparing the surrounding healthy tissue. Such a decision making process can be modeled as a mixed-integer linear programming (MILP) problem. In this paper, we introduce a novel MILP optimization model...
Source: Physics in Medicine and Biology - February 15, 2019 Category: Physics Authors: Babadagli ME, Sloboda R, Doucette J Tags: Phys Med Biol Source Type: research

2019: An Update from the Editor-in-Chief.
Abstract Not applicable. PMID: 30754025 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 12, 2019 Category: Physics Authors: Cherry SR Tags: Phys Med Biol Source Type: research

Investigation of the refractive index decrement of 3D printing materials for manufacturing breast phantoms for phase contrast imaging.
Abstract 3D breast modelling for 2D and 3D breast X-ray imaging would benefit from the availability of digital and physical phantoms that reproduce accurately the complexity of the breast anatomy. While a number of groups have produced digital phantoms with increasing level of complexity, physical phantoms reproducing that software approach have been scarcely developed. One possibility is offered by 3D printing technology. This implies the assessment of the energy dependent absorption index β of 3D printing materials for absorption based imaging, as well as the assessment of the refractive index decrement, &d...
Source: Physics in Medicine and Biology - February 12, 2019 Category: Physics Authors: Esposito G, Mettivier G, Bliznakova K, Bliznakov Z, Bosmans H, Bravin A, Buliev I, Di Lillo F, Ivanov D, Minutillo M, Sarno A, Vignero J, Russo P Tags: Phys Med Biol Source Type: research

Real-time respiratory triggered four dimensional cone-beam CT halves imaging dose compared to conventional 4D CBCT.
Abstract Four dimensional cone-beam computed tomography (4D CBCT) improves patient positioning and the accuracy of radiation therapy for patients with mobile tumours. Generally, 4D CBCT requires many hundreds of x-ray projections to measure target trajectories and the imaging frequency is not adapted to the patient's respiratory signal resulting in over-sampling. In contrast, respiratory triggered 4D CBCT (RT 4D CBCT) is an acquisition technique that has been experimentally implemented and has shown to reduce the number of x-ray projections and thus 4D CBCT dose with minimal impact on image quality. The aim of thi...
Source: Physics in Medicine and Biology - February 12, 2019 Category: Physics Authors: Cooper BJ, O'Brien RT, Shieh CC, Keall PJ Tags: Phys Med Biol Source Type: research

Joint correction of attenuation and scatter in image space using deep convolutional neural networks for dedicated brain < sup > 18 < /sup > F-FDG PET.
In conclusion, we demonstrated the feasibility of directly producing PET images corrected for attenuation and scatter using a DCNN (PET&lt;sub&gt;DCNN&lt;/sub&gt;) from PET&lt;sub&gt;NC&lt;/sub&gt; in image space without requiring conventional attenuation map generation and time-consuming scatter correction. Additionally, our DCNN-based method provides a possible alternative to MR-ASC for simultaneous PET/MRI. PMID: 30743246 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 11, 2019 Category: Physics Authors: Yang J, Park D, Gullberg GT, Seo Y Tags: Phys Med Biol Source Type: research

Relationship between power density and surface temperature elevation for human skin exposure to electromagnetic waves with oblique incidence angle from 6 GHz to 1 THz.
This study presents an investigation of human skin exposure to obliquely incident electromagnetic waves at frequencies from 6 GHz to 1 THz. We aim to clarify the relationship between the power density and the skin surface temperature elevation under various exposure conditions. A Monte Carlo simulation was conducted to assess the transmittance and surface temperature elevation considering the variation of skin tissue thickness. For the case of TM wave injection, transmittance increases with increasing incidence angle from the normal incidence because of the Brewster effect. The normal incidence is confirmed as the worst-ca...
Source: Physics in Medicine and Biology - February 8, 2019 Category: Physics Authors: Li K, Sasaki K, Watanabe S, Shirai H Tags: Phys Med Biol Source Type: research

Evaluation of materials used for vascular anastomoses using shear wave elastography.
In this study we used shear wave elastography (SWE) techniques to compare the mechanical behavior of excised aortas and anastomoses formed between the aortas and the Dacron, ePTFE, and PRAM materials. Different initial longitudinal strains (0-40%) and transmural pressures (20-180 mmHg) were used to test a wide range of parameters that are within physiological ranges. We found that the PRAM materials had similar mechanical behavior in terms of group velocity measured in the vessel wall with respect to the excised aortas compared to the Dacron and ePTFE that had higher values of group velocity. The ratios of the group veloci...
Source: Physics in Medicine and Biology - February 8, 2019 Category: Physics Authors: Bernal M, Sen I, Urban MW Tags: Phys Med Biol Source Type: research

Semi-automated IGRT QA using a cone-shaped scintillator screen detector for proton pencil beam scanning treatments.
This study presents an alternative and more efficient approach for IGRT QA for PBS and potentially for linear accelerators. . PMID: 30736026 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - February 8, 2019 Category: Physics Authors: Cai W, Oesten H, Clasie B, Winey B, Jee KW Tags: Phys Med Biol Source Type: research

A stochastic frontier analysis for enhanced treatment quality of high-dose-rate brachytherapy plans.
Abstract The purpose of the present study is to develop patient specific unbiased quality control (QC) models for high dose rate (HDR) brachytherapy plans. The proposed models are based on the stochastic frontier analysis formalism, a method of economic modeling. They act as a QC tool by predicting before the treatment planning process starts, the dosimetric coverage achievable for a HDR brachytherapy prostate plan. The geometric parameters considered in developing the models were: patient clinical target volume (CTV), organs at risk (OAR) volume, the bidirectional Hausdorff distance between CTV and OARs, and a f...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Edimo P, Kroshko A, Beaulieu L, Archambault L Tags: Phys Med Biol Source Type: research

Experimental measurements validate the use of the binary encounter approximation model to accurately compute proton induced dose and radiolysis enhancement from gold nanoparticles.
n AC Abstract In protontherapy, it has been suggested that nanoparticles of high-Z material like gold (GNP) be used as radiosensitizers. The origin of this enhancement phenomenon for proton radiation is not yet well understood and additional mechanistic insights are required. Previous works have highlighted the good capabilities of TRAX to reproduce secondary electron emission from gold material. Therefore, TRAX cross sections obtained with the binary encounter approximation (BEA) model for proton ionization were implemented within Geant4 for gold material. Based on the TRAX cross sections, improved Geant4 si...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Hespeels F, Lucas S, Tabarrant T, Scifoni E, Kraemer M, Chêne G, Strivay D, Tran HN, Heuskin AC Tags: Phys Med Biol Source Type: research

The effect of magnetic field strength on the response of Gafchromic EBT-3 film.
This study finds that there is at most a small effect of the magnetic field on the response of EBT-3 film. In terms of netOD (red channel) the change in response varied from ‒0.0011 at 0.5 T to 0.0045 at 2.0 T, with a standard uncertainty of 0.0030. If uncorrected, this would lead to an error in film-measured dose, for the red channel, of 2.4% at 2 T, with a standard uncertainty on dose of 1.4%. Results are also presented for B-field strengths of 0.5 T, 1 T and 1.5 T, which are all zero within the measurement uncertainty. Comparison between other studies is also presented. Considering the small change on dose deter...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Billas I, Bouchard H, Oelfke U, Duane S Tags: Phys Med Biol Source Type: research

Exploration of different X-ray Talbot-Lau setups for dark-field lung imaging examined in a porcine lung.
Abstract X-ray dark-field imaging is a promising technique for lung diagnosis. Due to the alveolar structure of lung tissue, a higher contrast is obtained by the dark-field image compared to the attenuation image. Animal studies indicate an enhancement regarding the detection of lung diseases in early stages. In this publication, we focus on the influence of different Talbot-Lau interferometer specifications while maintaining the X-ray source, sample magnification and detector system. By imaging the same porcine lung with three different grating sets, we analyze the contrast-to-noise ratio of the obtained dark-fie...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Ludwig V, Seifert M, Hauke C, Hellbach K, Horn F, Pelzer G, Radicke M, Rieger J, Sutter SM, Michel T, Anton G Tags: Phys Med Biol Source Type: research

Impact of high dose volumetric CT on PTV margin reduction in VMAT prostate radiotherapy.
Abstract The aim of the study is to determine PTV margin for inter-observer variability in the volumetric modulated arc therapy (VMAT) prostate radiotherapy with high-dose volumetric CT (HDVCT) and conventional helical CT (CCT) for planning. Secondly to investigate the impact of geometric (PTV expansion) and dosimetric (conformity) imperfection of planning process on the PTV margin analysis. Prostate gland of ten patients were scanned with CCT and HDVCT techniques consecutively on a 320 slice volumetric CT scanner with wide field detector of 16 cm. Five radiation oncologists delineated CTV of the prostate. VMAT pl...
Source: Physics in Medicine and Biology - February 7, 2019 Category: Physics Authors: Cho YB, Alasti H, Kong V, Catton C, Berlin A, Chung P, Bayley A, Jaffray DA Tags: Phys Med Biol Source Type: research

Recent advances in cardiac SPECT instrumentation and imaging methods.
Abstract Cardiac SPECT continues to play a critical role in detecting and managing cardiovascular disease, in particularly coronary artery disease (CAD) (Jaarsma et al., 2012; Agostini et al., 2016). While conventional dual-head SPECT scanners using parallel-hole collimators and scintillation crystals with photomultiplier tubes are still the workhorse of cardiac SPECT, they have the limitations of low photon sensitivity (~130 count s-1 MBq-1), poor image resolution (~15 mm) (Imbert et al., 2012), relatively long acquisition time, inefficient use of the detector, high radiation dose, etc. Recently our field observe...
Source: Physics in Medicine and Biology - February 6, 2019 Category: Physics Authors: Wu J, Liu C Tags: Phys Med Biol Source Type: research

Brain SAR of average male Korean child to adult models for mobile phone exposure assessment.
Abstract This paper aims to implement average head models of Korean males and investigate age-related differences in the brain for exposure from radiation from mobile phones. Four male head models composed of a total of 69 structures were developed through a statistical investigation of the anatomical morphology for the age groups of 6, 9, 15 and 20-24 years in age, which are named KR-6, KR-9, KR-15, and KR-22 herein. Three numerical bar phone models with a dual-band built-in antenna were applied to calculate the specific absorption rate (SAR) in the brain; the body lengths of models M avg and M long have the mean...
Source: Physics in Medicine and Biology - February 5, 2019 Category: Physics Authors: Lee AK, Park JS, Hong SE, Taki M, Wake K, Wiart J, Choi HD Tags: Phys Med Biol Source Type: research

Fast shading correction for cone-beam CT via partitioned tissue classification.
Abstract The quantitative use of cone beam computed tomography (CBCT) in radiation therapy is limited by severe shading artifacts, even with system embedded correction. We recently proposed effective shading correction methods, using planning CT (pCT) as prior information to estimate low-frequency errors in either the projection domain or the image domain. In this work, we further improve the clinical practicality of our previous methods by removing the requirement of prior pCT images. Clinical CBCT images are typically composed of a limited number of tissue types. By utilizing the low-frequency characterist...
Source: Physics in Medicine and Biology - February 5, 2019 Category: Physics Authors: Shi L, Wang AS, Wei J, Zhu L Tags: Phys Med Biol Source Type: research

Quantification of myocardial uptake rate constants in dynamic small-animal SPECT using a cardiac phantom.
Abstract Myocardial blood flow and myocardial blood flow reserve (MBFR) measurements are often used clinically to quantify coronary microvascular function. Developing imaging-based methods to measure MBFR for research in mice would be advantageous for evaluating new treatment methods for coronary microvascular disease, yet this is more challenging in mice than in humans. This work investigates microSPECT's quantitative capabilities of cardiac imaging by utilizing a multi-part cardiac phantom and applying a known kinetic model to synthesize kinetic data from static data, allowing for assessment of kinetic modeling ...
Source: Physics in Medicine and Biology - February 5, 2019 Category: Physics Authors: Johnson LC, Guerraty MA, Moore SC, Metzler SD Tags: Phys Med Biol Source Type: research

Fast optimized Monte Carlo phase-space generation and dose prediction for low energy X-ray intra-operative radiation therapy.
, Udías JM Abstract Low energy X-ray Intra-Operative Radiation Therapy (IORT) is used mostly for breast cancer treatment with spherical applicators. X-ray IORT treatment delivered during surgery (ex: INTRABEAM®, Carl Zeiss) can benefit from accurate and fast dose prediction in a patient 3D volume. However, full Monte Carlo (MC) simulations are time-consuming and no commercial treatment planning system was available for this treatment delivery technique. Therefore, the aim of this work is to develop a dose computation tool based on MC phase space information, which computes fast and accurate dose distrib...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Vidal M, Ibáñez P, Guerra P, Valdivieso-Casique MF, Rodriguez R, Illana C, Udías JM Tags: Phys Med Biol Source Type: research

Towards patient connected imaging with ACROBEAT: Adaptive CaRdiac cOne BEAm computed Tomography.
Abstract Robotic C-arm Cone Beam Computed Tomography (CBCT) systems are playing an increasingly pivotal role in interventional cardiac procedures and high precision radiotherapy treatments. One of the main challenges in any form of cardiac imaging is mitigating the intrinsic motion of the heart, which causes blurring and artefacts in the 3D reconstructed image. Most conventional 3D cardiac CBCT acquisition techniques attempt to combat heart motion through retrospective gating techniques, whereby acquired projections are sorted into the desired cardiac phase after the completion of the scan. However, this results i...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Reynolds T, Shieh CC, Keall PJ, O'Brien RT Tags: Phys Med Biol Source Type: research

Functional imaging of tumor vasculature using iodine and gadolinium-based nanoparticle contrast agents: a comparison of spectral micro-CT using energy integrating and photon counting detectors.
Abstract Advances in computed tomography (CT) hardware have propelled the development of novel CT contrast agents. In particular, the spectral capabilities of X-ray CT can facilitate simultaneous imaging of multiple contrast agents. This approach is particularly useful for functional imaging of solid tumors by simultaneous visualization of multiple targets or architectural features that govern cancer development and progression. Nanoparticles are a promising platform for contrast agent development. While several novel imaging moieties based on high atomic number elements are being explored, iodine (I) and gadolini...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Badea CT, Clark DP, Holbrook M, Srivastava M, Mowery Y, Ghaghada KB Tags: Phys Med Biol Source Type: research

Microvascular imaging of the skin.
Abstract Despite our understanding that the microvasculature plays a multifaceted role in the development and progression of various conditions, we know little about the extent of this involvement. A need exists for non-invasive, clinically meaningful imaging modalities capable of elucidating microvascular information to aid in our understanding of disease, and to aid in the diagnosis/monitoring of disease for more patient-specific care. In this review article, a number of imaging techniques are summarized that have been utilized to investigate the microvasculature of skin, along with their advantages, disadvantag...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Deegan AJ, Wang RR Tags: Phys Med Biol Source Type: research

Regularised patient-specific stopping power calibration for proton therapy planning based on proton radiographic images.
Abstract Proton transmission imaging has been proposed and investigated as imaging modality complementary to X-ray based techniques in proton beam therapy. In particular, it addresses the issue of range uncertainties due to the conversion of an X-ray patient computed tomography (CT) image expressed in Hounsfield Units (HU) to relative stopping power (RSP) needed as input to the treatment planning system. One approach to exploit a single proton radiographic projection is to perform a patient-specific calibration of the CT to RSP conversion curve by optimising the match between a measured and a numerically integrate...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Krah N, Patera V, Rit S, Schiavi A, Rinaldi I Tags: Phys Med Biol Source Type: research

Effects of posture on electric fields of non-invasive brain stimulation.
This study aimed to determine whether small inter-postural changes in the shape of the brain can affect TDCS and TMS EFs as hypothesized. We obtained MRI from five subjects in each position and used them to build anatomically realistic models for use in finite element simulations of the EFs. Position was found to affect EFs, with them being approximately 10% stronger and more diffuse while subjects were in the prone and left lateral than in the supine positions for TDCS. In TMS, a similar trend was observed, but the effect was smaller, approximately 2%, than that observed for TDCS. Thus, the effect of posture should be con...
Source: Physics in Medicine and Biology - February 1, 2019 Category: Physics Authors: Mikkonen M, Laakso I Tags: Phys Med Biol Source Type: research

Malignant-benign classification of pulmonary nodules based on random forest aided by clustering analysis.
Abstract To help the radiologists better differentiate the benign from malignant pulmonary nodules on CT images, a novel classification scheme was proposed to improve the performance of benign and malignant classifier of pulmonary nodules. First, the pulmonary nodules were segmented with the references to the results from four radiologists. Then, some basic features of the segmented nodules such as the shape, gray and texture are given by calculation. Finally, malignant-benign classification of pulmonary nodules is performed by using random forest (RF) with the aid of clustering analysis. The data with a set of 95...
Source: Physics in Medicine and Biology - January 31, 2019 Category: Physics Authors: Wu W, Hu H, Gong J, Li X, Huang G, Nie S Tags: Phys Med Biol Source Type: research

Analytical model of DOI-induced time bias in ultra-fast scintillation detectors for TOF-PET.
Abstract In Positron Emission Tomography (PET), long crystals (≥20 mm) are used to enhance detection efficiency and increase scanner sensitivity. However, for fast time-of-flight (TOF) scanners, this may affect the achievable coincidence time resolution (CTR) due to depth-of-interaction (DOI) induced blur on timing. Currently, the effect of DOI on CTR evaluation with analytical modeling is incorporated using the probability density function (PDF) for attenuation of the annihilation photons with the PDFs of the other scintillation processes. However, we show that the resulting PDF would not describe accurately t...
Source: Physics in Medicine and Biology - January 31, 2019 Category: Physics Authors: Toussaint M, Loignon-Houle F, Dussault JP, Lecomte R Tags: Phys Med Biol Source Type: research

Three-dimensional radiotherapy dose prediction on head and neck cancer patients with a hierarchically densely connected U-net deep learning architecture.
Abstract The treatment planning process for patients with head and neck (H&N) cancer is regarded as one of the most complicated due to large target volume, multiple prescription dose levels, and many radiation-sensitive critical structures near the target. Treatment planning for this site requires a high level of human expertise and a tremendous amount of effort to produce personalized high quality plans, taking as long as a week, which deteriorates the chances of tumor control and patient survival. To solve this problem, we propose to investigate a deep learning-based dose prediction model, Hierarchically Den...
Source: Physics in Medicine and Biology - January 31, 2019 Category: Physics Authors: Nguyen D, Jia X, Sher D, Lin MH, Iqbal Z, Liu H, Jiang SB Tags: Phys Med Biol Source Type: research

Effects of transverse heterogeneities on the most likely path of protons.
Rit S Abstract The use of a most likely path (MLP) formalism for protons to account for the effects of multiple Coulomb scattering has improved the spatial resolution in proton computed tomography (pCT). However, this formalism assumes a homogeneous medium and a continuous scattering of protons. In this paper, we quantify the path prediction error induced by transverse heterogeneities to assess whether correcting for such errors might improve the spatial resolution of pCT. To this end, we have tracked protons trajectories using Monte Carlo simulations in several phantoms with different heterogeneities. Our results...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Khellaf F, Krah N, Rinaldi I, Létang JM, Rit S Tags: Phys Med Biol Source Type: research

Phantom evaluations of low frequency MR elastography.
This study explores low frequency actuation (1 Hz) MR elastography in phantoms and analyzes performance of non-linear inversion (NLI) of viscoelastic and poroelastic mechanical models as a framework for assessing clinical results from IA-MRE. We present results from four gelatin phantoms and report stiffness resolution of 6 mm (two measurement voxels) with a stiffness contrast ratio of 4.21 relative to the background and 9 mm (three measurement voxels) with a lower stiffness contrast ratio of near 1.77. Stiffness edge resolution was also evaluated using edge spread and line spread functions and yielded a stiffness edge res...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Solamen LM, Gordon-Wylie SW, McGarry MDJ, Weaver JB, Paulsen KD Tags: Phys Med Biol Source Type: research

A dual-purpose MRI acquisition to combine 4D-MRI and dynamic contrast-enhanced imaging for abdominal radiotherapy planning.
Abstract For successful abdominal radiotherapy it is crucial to have a clear tumor definition and an accurate characterization of the motion. While dynamic contrast-enhanced (DCE) MRI aids tumor visualization, it is often hampered by motion artifacts. 4D-MRI characterizes this motion, but often lacks the contrast to clearly visualize the tumor. This dual requirement is challenging due to time constraints. Here, we propose combining both into a single acquisition by reconstructing the data in various ways in order to achieve both high spatio-temporal resolution DCE-MRI and accurate 4D-MRI motion estimates....
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Stemkens B, Prins FM, Bruijnen T, Kerkmeijer LGW, Lagendijk JJW, Van den Berg CAT, Tijssen RHN Tags: Phys Med Biol Source Type: research

Unsupervised respiratory signal extraction from ungated cardiac magnetic resonance imaging at rest and during exercise.
Abstract We propose and evaluate a method to estimate a respiratory signal from ungated cardiac magnetic resonance (CMR) images. Ungated CMR images were acquired in 5 subjects who performed exercise at different intensity levels under different physiological conditions while breathing freely. The respiratory motion was estimated by applying principal components analysis (PCA). A sign correction procedure was developed to correctly define inspiration and expiration, based on either tracking of the diaphragmatic motion or estimation of the lung volume or a combination of both. Evaluation was done using a pleth...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Novillo F, Van Eyndhoven S, Moeyersons J, Bogaert J, Claessen G, La Gerche A, Van Huffel S, Claus P Tags: Phys Med Biol Source Type: research

FLUKA particle therapy tool for Monte Carlo independent calculation of scanned proton and carbon ion beam therapy.
s V Abstract While Monte Carlo (MC) codes are considered as the gold standard for dosimetric calculations, the availability of user friendly MC codes suited for particle therapy is limited. Based on the FLUKA MC code and its graphical user interface (GUI) Flair, we developed an easy-to-use tool which enables simple and reliable simulations for particle therapy. In this paper we provide an overview of functionalities of the tool and with the presented clinical, proton and carbon ion therapy examples we demonstrate its reliability and the usability in the clinical environment and show its flexibility for research pu...
Source: Physics in Medicine and Biology - January 29, 2019 Category: Physics Authors: Kozłowska WS, Böhlen TT, Cuccagna C, Ferrari A, Fracchiolla F, Georg D, Magro G, Mairani A, Schwarz M, Vlachoudis V Tags: Phys Med Biol Source Type: research