Recovery of inter-detector and inter-crystal scattering in brain PET based on LSO and GAGG crystals.
In conclusion, we showed that the proportional method would be suitable for IDS and ICS recoveries of PET, and emphasized the importance of ICS and IDS recoveries for PET using crystals with low stopping power. PMID: 32575086 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - June 23, 2020 Category: Physics Authors: Lee S, Kim KY, Lee MS, Lee JS Tags: Phys Med Biol Source Type: research

4D-AirNet: a temporally-resolved CBCT slice reconstruction method synergizing analytical and iterative method with deep learning.
Abstract Four-dimensional (4D) cone-beam CT (CBCT) reconstructs temporally-resolved phases of 3D volumes often with the same amount of projection data that are meant for reconstructing a single 3D volume. 4D CBCT is a sparse-data problem that is very challenging for high-quality 4D CBCT image reconstruction. Here we develop a new method, namely 4D-AirNet, that synergizes analytical and iterative method with deep learning for high-quality temporally-resolved CBCT slice reconstruction. 4D-AirNet is an unrolling method using the optimization framework of fused analytical and iterative reconstruction (AIR), which is b...
Source: Physics in Medicine and Biology - June 23, 2020 Category: Physics Authors: Chen G, Zhao Y, Huang Q, Gao H Tags: Phys Med Biol Source Type: research

Functionally weighted airway sparing (FWAS): a functional avoidance method for preserving post-treatment ventilation in lung radiotherapy.
Abstract Recent changes to the guidelines for screening and early diagnosis of lung cancer have increased the interest in preserving post-radiotherapy lung function. Current investigational approaches are based on spatially mapping functional regions and generating regional avoidance plans that preferentially spare highly ventilated/perfused lung. A potentially critical, yet overlooked, aspect of functional avoidance is radiation injury to peripheral airways, which serve as gas conduits to and from functional lung regions. Dose redistribution based solely on regional function may cause irreparable damage to the &q...
Source: Physics in Medicine and Biology - June 23, 2020 Category: Physics Authors: Vicente E, Modiri A, Kipritidis J, Hagan A, Yu KC, Wibowo H, Yan Y, Owen DR, Matuszak MM, Mohindra P, Timmerman RD, Sawant A Tags: Phys Med Biol Source Type: research

A robust optimization method for weighted-layer-stacking proton beam therapy.
Abstract The layer-stacking method can provide three-dimensional conformal dose distributions to the target based on a passive scattering method using mini-spread-out Bragg peak (SOBP). The purpose of this work is to demonstrate the effectiveness of a new weight optimization algorithm that can enhance the robustness of dose distributions against layer depth variation in layer-stacking proton beam therapy. In the robustness algorithm, the upper limit of the layer's weight was adapted to the conventional algorithm and varied for 620 weight set evaluations. The optimal weight set was selected by using an analytical o...
Source: Physics in Medicine and Biology - June 22, 2020 Category: Physics Authors: Sakamoto Y, Maeda Y, Yamada Y, Ikeda M, Tameshige Y, Sasaki M, Shibata S, Yamamoto K Tags: Phys Med Biol Source Type: research

Characterization of a multi-pinhole molecular breast tomosynthesis scanner.
Abstract In recent years, breast imaging using radiolabelled molecules has attracted significant interest. Our group has proposed a multi-pinhole molecular breast tomosynthesis (MP-MBT) scanner to obtain 3D functional molecular breast images at high resolutions. After conducting extensive optimisation studies using simulations we here present a first prototype of MP-MBT and evaluate its performance using physical phantoms. The MP-MBT design is based on two opposing gamma cameras that can image a lightly compressed pendant breast. Each gamma camera consists of a 250×150 mm2detector equipped with a collimator ...
Source: Physics in Medicine and Biology - June 22, 2020 Category: Physics Authors: Wang B, van Roosmalen J, Kreuger R, Huizenga J, Beekman FJ, Goorden MC Tags: Phys Med Biol Source Type: research

Improving depth-of-interaction resolution in pixellated PET detectors using neural networks.
Abstract Parallax error is a common issue in high-resolution preclinical positron emission tomography (PET) scanners as well as in clinical scanners that have a long axial field of view (FOV), which increases estimation uncertainty of the annihilation position and therefore degrades the spatial resolution. A way to address this issue is depth-of-interaction (DOI) estimation. In this work we propose two machine learning-based algorithms, a dense and a convolutional neural network (NN), as well as a multiple linear regression (MLR)-based method to estimate DOI in depolished PET detector arrays with single-sided read...
Source: Physics in Medicine and Biology - June 22, 2020 Category: Physics Authors: Zatcepin A, Pizzichemi M, Polesel A, Paganoni M, Auffray E, Ziegler SI, Omidvari N Tags: Phys Med Biol Source Type: research

Reference dosimetry in MRI-linacs: evaluation of available protocols and data to establish a code of practice.
Abstract With the rapid increase in clinical treatments with MRI-linacs, a consistent, harmonized and sustainable ground for reference dosimetry in MRI-linacs is needed. Specific for reference dosimetry in MRI-linacs is the presence of a strong magnetic field. Therefore, existing Code of Practices (CoPs) are inadequate. In recent years, a vast amount of papers has been published in relation to this topic. The purpose of this review paper is twofold: to give an overview and evaluate the existing literature for reference dosimetry in MRI-linacs and to discuss whether this literature and datasets are adequate and com...
Source: Physics in Medicine and Biology - June 22, 2020 Category: Physics Authors: de Pooter JA, Billas I, de Prez LA, Duane S, Kapsch RP, Karger C, van Asselen B, Wolthaus JWH Tags: Phys Med Biol Source Type: research

Low dose lung radiation therapy for pneumonia: an examination of historical dose distributions.
Abstract The novel coronavirus, SARS-CoV-2, that causes the COVID-19 disease currently has healthcare systems around the world dealing with unprecedented numbers of critically ill patients. One of the primary concerns associated with this illness is acute respiratory distress syndrome (ARDS) and the pneumonia that accompanies it. Historical literature dating back to the 1940s and earlier contains many reports of successful treatment of pneumonias with ionizing radiation. Although these were not randomized controlled trials, they do suggest a potential avenue for further investigation. Technical details in these re...
Source: Physics in Medicine and Biology - June 18, 2020 Category: Physics Authors: Kirkby C, Mackenzie M Tags: Phys Med Biol Source Type: research

Microdosimetric measurements as a tool to assess potential in- and out-of-field toxicity regions in proton therapy.
In this study, we exploited microdosimetry for characterizing radiation quality in proton therapy in-field, and off-beam at 20 (beam-edge), 50 (close-out-of-field) and 100 (far out-of-field) mm from beam center. We measured lineal energy y spectra in a water phantom irradiated with 152 MeV protons, from which beam quality as well as the physical dose could be obtained. Taking advantage of the Linear Quadratic (LQ) and a modified version of the Microdosimetric Kinetic (MKM) models, the microdosimetric data were combined with radiobiological parameters (α and β) of Human Salivary Gland (HSG) tumor cells for assess...
Source: Physics in Medicine and Biology - June 18, 2020 Category: Physics Authors: Missiaggia M, Cartechini G, Scifoni E, Rovituso M, Tommasino F, Verroi E, Durante M, La Tessa C Tags: Phys Med Biol Source Type: research

Adaptive noise reduction for dual-energy x-ray imaging based on spatial variations in beam attenuation.
CONCLUSION: Theoretical expressions of CNR and SNR functions were derived and validated by experimental data. The ACNR weighting factors have a dependency on the material thicknesses. The adaptive ANCR dual-energy algorithm was developed, which allows for an increase of the image quality by spatially varying weighting factors for noise reduction. PMID: 32554889 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - June 18, 2020 Category: Physics Authors: Romadanov I, Sattarivand M Tags: Phys Med Biol Source Type: research

Treatment effect prediction for sarcoma patients treated with preoperative radiotherapy using radiomics features from longitudinal diffusion-weighted MRI.
Abstract PURPOSE: To explore radiomics features from longitudinal diffusion-weighted MRI (DWI) for pathologic treatment effect prediction in patients with localized soft tissue sarcoma (STS) undergoing hypofractionated preoperative radiotherapy (RT). METHODS: Thirty patients with localized STS treated with preoperative hypofractionated RT were recruited to this longitudinal imaging study. DWI were acquired at three time points using a 0.35T MRI-guided radiotherapy system. Treatment effect score (TES) was obtained from the post-surgery pathology as a surrogate of treatment outcome. Patients were divided into t...
Source: Physics in Medicine and Biology - June 18, 2020 Category: Physics Authors: Gao Y, Kalbasi A, Hsu W, Ruan D, Fu J, Shao J, Cao M, Wang C, Eilber FC, Bernthal N, Bukata S, Dry SM, Nelson S, Kamrava M, Lewis JH, Low DA, Steinberg M, Hu P, Yang Y Tags: Phys Med Biol Source Type: research

A modular phantom and software to characterize 3D geometric distortion in MRI.
Abstract Magnetic resonance imaging (MRI) offers outstanding soft tissue contrast that may reduce uncertainties in target and organ-at-risk delineation and enable online adaptive image-guided treatment. Spatial distortions resulting from non-linearities in the gradient fields and non-uniformity in the main magnetic field must be accounted for across the imaging field-of-view to prevent systematic errors during treatment delivery. This work presents a modular phantom and software application to characterize geometric distortion (GD) within the large field-of-view MRI images required for radiation therapy simulation...
Source: Physics in Medicine and Biology - June 12, 2020 Category: Physics Authors: Slagowski JM, Ding Y, Aima M, Wen Z, Fuller CD, Chung C, Debnam JM, Hwang KP, Kadbi M, Szklaruk J, Wang J Tags: Phys Med Biol Source Type: research

Two high-resolution thermal monitoring sheets for clinical superficial hyperthermia.
Abstract PURPOSE: Temperature measurement during superficial hyperthermia is limited by poor spatial resolution. We investigated two sheets to improve temperature monitoring of the skin surface. METHODS AND MATERIALS: Two different sheets were studied with a grid of temperature sensors with one sensor per ~5 cm2. The first was a matrix of multisensor thermocouple probes laced through a silicone sheet. The second sheet had rows of thermistors connected by meandering copper leads mounted on stretchable printed circuit board (SPCB). Accuracy, temperature resolution and two hour stability of both sheets were inve...
Source: Physics in Medicine and Biology - June 11, 2020 Category: Physics Authors: Bakker A, Zweije R, van Tienhoven G, Kok HP, Sijbrands J, van den Bongard D, Rasch C, Crezee H Tags: Phys Med Biol Source Type: research

Using a small-core graphite calorimeter for dosimetry and scintillator quenching corrections in a therapeutic proton beam.
Abstract Organic plastic scintillation detectors (PSDs) are known to produce less light per absorbed dose in highly dense radiations in comparison with e.g.60Co gamma beams. This so-called ionization density quenching can be experimentally determined by comparison of the scintillator output with the absorbed dose established with a reference detector. The hypothesis of this work was that a newly developed small-core graphite calorimeter (core size: ø5mm × 7mm) can be used as reference for such measurements. The potential benefit of a calorimetric reference would be to have a robust and accurate refere...
Source: Physics in Medicine and Biology - June 11, 2020 Category: Physics Authors: Christensen JB, Vestergaard A, Andersen CE Tags: Phys Med Biol Source Type: research

Intensity modulated Ir-192 brachytherapy using high-Z 3D printed applicators.
Abstract Gynecologic cancers are often asymmetric, yet current Ir-192 brachytherapy techniques provide only limited radial modulation of the dose. The shielded solutions investigated here solve this by providing the ability to modulate between highly asymmetric and radially symmetric dose distributions at a given location. To find applicator designs that can modulate between full dose and less than 50% dose, at the dimensions of the urethra, a 2D calculation algorithm was developed to narrow down the search space. Two shielding design types were then further investigated using Monte Carlo and Boltzmann-solver dose...
Source: Physics in Medicine and Biology - June 10, 2020 Category: Physics Authors: Skinner LB, Niedermayr T, Prionas N, Perl J, Fahimian BP, Kidd E Tags: Phys Med Biol Source Type: research

An improved beam splitting method for intensity modulated proton therapy.
Abstract Pencil beam algorithm (PBA) has become the predominant dose calculation method in proton therapy due to high efficiency. However, density heterogeneity decreased the accuracy of PBA. To improve PBA's accuracy, beam splitting method was used which divides the original scanning beam into multiple thinner beamlets. Beam splitting should ensure that the beamlets' summed fluence is as close to the original beam fluence as possible, while keeping the spatial variance of beamlets small and minimizing the number of beamlets. In this work, the generalized differential evolution (GDE) algorithm was utilized for the...
Source: Physics in Medicine and Biology - June 10, 2020 Category: Physics Authors: Yang J, He P, Wang H, Sun G, Zheng H, Jia J Tags: Phys Med Biol Source Type: research

A tri-hybrid method to estimate the patient-generated scattered photon fluence components to the EPID image plane.
Abstract In vivo dosimetry methods can verify the prescription dose is delivered to the patient during treatment. Unfortunately, in exit dosimetry, the megavoltage image is contaminated with patient-generated scattered photons. However, estimation and removal of the effect of this fluence improves accuracy of in vivo dosimetry methods. This work develops a 'tri-hybrid' algorithm combining analytical, Monte Carlo (MC), and pencil-beam scatter kernel methods to provide accurate estimates of the total patient-generated scattered photon fluence entering the MV imager. For the multiply-scattered photon fluence, a modif...
Source: Physics in Medicine and Biology - June 9, 2020 Category: Physics Authors: Guo K, Ingleby H, Van Uytven E, Elbakri I, Van Beek T, McCurdy B Tags: Phys Med Biol Source Type: research

Scattering kernels for fast neutron therapy treatment planning.
t RD Abstract The University of Washington (UW) Clinical Neutron Therapy System (CNTS) has been used to treat over 3300 patients. Treatment planning for these patients is currently performed using an MV x-ray model in Pinnacle® adapted to fit measurements of fast neutron output factors, wedge factors, depth-dose and lateral profiles. While this model has provided an adequate representation of the CNTS for treatment planning, later versions of Pinnacle did not allow for machines with a source-to-axial distance of 150 cm, which has restricted the neutron model to version 9.0 while the photon and electron treatme...
Source: Physics in Medicine and Biology - June 8, 2020 Category: Physics Authors: Moffitt GB, Wootton LS, Hårdemark B, Sandison GA, Laramore GE, Parvathaneni U, Stewart RD Tags: Phys Med Biol Source Type: research

X-ray image quality and system exposure parameters for a hybrid Angio-MR system.
This study investigates the exposure parameters and required x-ray tube output when performing neurological procedures on a hybrid Angio-MR concept system proposed by Siemens Healthineers. The x-ray part of this system uses a longer source to detector distance than conventional (C-arm) systems and will have a fixed amount of filtration. Additionally, as the x-ray source is situated inside a magnetic field, the focal spot size and shape may be slightly distorted. In order to compare the Angio-MR system to a typical C-arm system, the exposure parameters of 60 thrombectomy procedures, performed in our hospital over the course...
Source: Physics in Medicine and Biology - June 8, 2020 Category: Physics Authors: Dehairs M, Bosmans H, Leghissa M, Marshall NW Tags: Phys Med Biol Source Type: research

A heterogenous, time harmonic, nearly incompressible transverse isotropic finite element brain simulation platform for MR elastography.
In this study, we describe numerical implementation of a heterogenous, nearly incompressible, transverse isotropic (NITI) finite element (FE) model with key advantages for use in MR elastography of fibrous soft tissue. MR elastography (MRE) estimates heterogenous property distributions from MR-measured harmonic motion fields based on assumed mechanical models of tissue response. Current MRE property estimation methods usually assume isotropic properties, which cause inconsistencies arising from model-data mismatch when anisotropy is present. In this study, we use a NITI model parameterized by a base shear modulus, shear an...
Source: Physics in Medicine and Biology - June 8, 2020 Category: Physics Authors: McGarry MDJ, Van Houten E, Guertler C, Okamoto RJ, Smith DR, Sowinski DR, Johnson CL, Bayly P, Weaver J, Paulsen KD Tags: Phys Med Biol Source Type: research

C-arm CT imaging with the extended line-ellipse-line trajectory: first implementation on a state-of-the-art robotic angiography system.
Abstract Three-dimensional cone-beam imaging has become valuable in interventional radiology. Currently, this tool, referred to as C-arm CT, employs a circular short-scan for data acquisition, which limits the axial volume coverage and yields unavoidable cone-beam artifacts. To improve flexibility in axial coverage and image quality, there is a critical need for novel data acquisition geometries and related image reconstruction algorithms. For this purpose, we previously introduced the extended line-ellipse-line trajectory, which allows complete scanning of arbitrary volume lengths in the axial direction together ...
Source: Physics in Medicine and Biology - June 8, 2020 Category: Physics Authors: Guo Z, Lauritsch G, Maier A, Kugler P, Islam M, Vogt F, Noo F Tags: Phys Med Biol Source Type: research

Reducing PNS with minimal performance penalties via simple pulse sequence modifications on a high-performance compact 3T scanner.
Abstract One of the major concerns associated with high-performance gradients is peripheral nerve stimulation (PNS) of the subject during MRI exams. Since the installation, more than 680 volunteer subjects (patients and controls) have been scanned on a compact 3T MRI system with high-performance gradients, capable of 80 mT/m gradient amplitude and 700 T/m/s slew rate simultaneously. Despite PNS concerns associated with the high-performance gradients, due to the smaller physical dimensions of the gradient coils, minimal or no PNS sensation was reported with most pulse sequences. The exception was PNS reported by on...
Source: Physics in Medicine and Biology - June 5, 2020 Category: Physics Authors: In MH, Shu Y, Trzasko JD, Yarach U, Kang D, Gray EM, Huston Iii J, Bernstein MA Tags: Phys Med Biol Source Type: research

Multi-energy CT imaging for large patients using dual-source photon-counting detector CT.
Abstract Multi-energy CT imaging of large patients with conventional dual-energy (DE)-CT using an energy-integrating-detector (EID) is challenging due to photon starvation-induced image artifacts, especially in lower tube potential (80-100 kV) images. Here, we performed phantom experiments to investigate the performance of DECT for morbidly obese patients, using an iodine and water material decomposition task as an example, on an emulated dual-source (DS)-photon-counting-detector (PCD)-CT, and compared its performance with a clinical DS-EID-CT. An abdominal CT phantom with iodine inserts of different concentration...
Source: Physics in Medicine and Biology - June 5, 2020 Category: Physics Authors: Tao S, Marsh JF, Tao A, Michalak GJ, Rajendran K, McCollough CH, Leng S Tags: Phys Med Biol Source Type: research

IPEM code of practice for high-energy photon therapy dosimetry based on the NPL absorbed dose calibration service.
Abstract The 1990 code of practice (COP), produced by the IPSM (now the Institute of Physics and Engineering in Medicine, IPEM) and the UK National Physical Laboratory (NPL), gave instructions for determining absorbed dose to water for megavoltage photon (MV) radiotherapy beams (Lillicrap et al. Phys. Med. Biol. 1990 35 1355-60). The simplicity and clarity of the 1990 COP led to widespread uptake and high levels of consistency in external dosimetry audits. An addendum was published in 2014 to include the non-conventional conditions in Tomotherapy units. However, the 1990 COP lacked detailed recommendations for cal...
Source: Physics in Medicine and Biology - June 5, 2020 Category: Physics Authors: Eaton DJ, Bass GA, Booker P, Byrne J, Duane S, Frame J, Grattan MWD, Thomas RAS, Thorp N, Nisbet A Tags: Phys Med Biol Source Type: research

Robustness study of noisy annotation in deep learning based medical image segmentation.
This study suggests that the involved network is robust to noisy annotation to some extent in mandible segmentation from CT images. It also highlights the importance of labeling quality in deep learning. In the future work, extra attention should be paid on how to utilize a small number of reference standard samples to improve the performance of deep learning with noisy annotation. PMID: 32503027 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - June 5, 2020 Category: Physics Authors: Yu S, Chen M, Zhang E, Wu J, Yu H, Yang Z, Ma L, Gu X, Lu W Tags: Phys Med Biol Source Type: research

Flat-panel imager energy-dependent proton radiography for a proton pencil-beam scanning system.
Abstract In proton-based radiotherapy, proton radiography could allow for direct measurement of the water-equivalent path length (WEPL) in tissue, which can then be used to determine relative stopping power (RSP). Additionally, proton radiographs allow for imaging in the beam's-eye-view. In this work, a proton radiography technique using a flat-panel imager and a pencil-beam scanning (PBS) system is demonstrated in phantom. Proton PBS plans were delivered on a Varian ProBeam system to a flat-panel imager. Each proton plan consisted of energy layers separated by 4.8 MeV, and a field size of 25 cm × 25 cm. All...
Source: Physics in Medicine and Biology - June 4, 2020 Category: Physics Authors: Harms JM, Maloney L, Sohn JJ, Erickson A, Lin Y, Zhang R Tags: Phys Med Biol Source Type: research

Electron density and effective atomic number estimation in a maximum a posteriori framework for dual-energy computed tomography.
CONCLUSION: Theoretical and experimental results suggest that the MAP framework produces more accurate and precise estimates of the electron density and SPR. Thus, the present approach limits the propagation of noise in DECT attenuation data to radiotherapy-related parameters maps such as the SPR and the electron density. Using a MAP framework with DECT for radiotherapy treatment planning can help maximizing the precision of dose calculation. The method also provides more precise estimates of the effective atomic number. The MAP methodology is presented in a general way such that it can be adapted to any DECT image-based t...
Source: Physics in Medicine and Biology - June 3, 2020 Category: Physics Authors: Simard M, Bär E, Blais D, Bouchard H Tags: Med Phys Source Type: research

Neural networks-based regularization for large-scale medical image reconstruction.
Abstract In this paper we present a generalized Deep Learning-based approach for solving ill-posed large-scale inverse problems occuring in medical image reconstruction. Recently, Deep Learning methods using iterative neural networks and cascaded neural networks have been reported to achieve state-of-the-art results with respect to various quantitative quality measures as PSNR, NRMSE and SSIM across different imaging modalities. However, the fact that these approaches employ the forward and adjoint operators repeatedly in the network architecture requires the network to process the whole images or volumes at once,...
Source: Physics in Medicine and Biology - June 3, 2020 Category: Physics Authors: Kofler A, Haltmeier M, Schaeffter T, Kachelriess M, Dewey M, Wald C, Kolbitsch C Tags: Phys Med Biol Source Type: research

Evaluating reconstruction algorithms for respiratory motion guided acquisition.
Abstract Conventional thoracic 4DCBCT scans take 1,320 projections over 4 minutes. This paper investigates which reconstruction algorithms best leverage Respiratory-Motion-Guided (RMG) acquisition in order to reduce scan time and dose while maintaining image quality. We investigated a 200 projection, on average 1-minute RMG acquisition. RMG acquisition ensures even angular separation between projections at each respiratory phase by adjusting the imaging gantry rotation to the patient respiratory signal in real time. Conventional 1,320 projection data and RMG 200 projection data were simulated from 4DCT volumes of ...
Source: Physics in Medicine and Biology - June 2, 2020 Category: Physics Authors: Dillon O, Keall PJ, Shieh CC, O'Brien RT Tags: Phys Med Biol Source Type: research

Extension of the ML-EM algorithm for dose estimation using PET in proton therapy: application to an inhomogeneous target.
In this study, a method for estimating the dose distribution from the positron emitter distributions was developed using the maximum likelihood expectation maximization algorithm. The 1D spatial relationship between positron emitter distributions and a dose distribution in an inhomogeneous target was inputted into the system matrix based on a filter framework. In contrast, spatial resolution of the PET system and total variation regularization (as prior knowledge for dose distribution) were considered in the 3D image-space. The dose estimation was demonstrated using Monte Carlo simulated PET activity distributions with sub...
Source: Physics in Medicine and Biology - June 2, 2020 Category: Physics Authors: Masuda T, Nishio T, Sano A, Karasawa K Tags: Phys Med Biol Source Type: research

Monte-Carlo-computed dose, kerma and fluence distributions in heterogeneous slab geometries irradiated by small megavoltage photon fields.
Abstract Small-field dosimetry is central to the planning and delivery of radiotherapy to patients with cancer. Small-field dosimetry is beset by complex issues, such as loss of charged-particle equilibrium (CPE), source occlusion and electron scattering effects in low-density tissues. The purpose of the present research was to elucidate the fundamental physics of small fields through the computation of absorbed dose, kerma and fluence distributions in heterogeneous media using the Monte-Carlo method. Absorbed dose and kerma were computed using the DOSRZnrc Monte-Carlo (MC) user-code for beams with square field si...
Source: Physics in Medicine and Biology - June 2, 2020 Category: Physics Authors: Kumar S, Nahum AE, Chetty IJ Tags: Phys Med Biol Source Type: research

Verification of dose distribution in high-dose-rate brachytherapy using a nanoclay-based radio-fluorogenic gel dosimeter.
In this study, using an Iridium-192 (Ir-192) source, we evaluated the basic characteristics of a nanoclay-based radio-fluorogenic gel (NC-RFG) dosimeter that is a fluorescent gel dosimeter using dihydrorhodamine 123 hydrochloride (DHR 123) as a fluorescent probe. The two-dimensional dose distribution measurements were performed at multiple source positions to simulate a clinical plan. Fluorescence images of the irradiated NC-RFG were obtained at a high resolution (0.04 mm/pixel) using a gel scanner with excitation at 465 nm. Good linearity was confirmed up to a dose range of 100 Gy without dose rate dependence. The dose di...
Source: Physics in Medicine and Biology - June 2, 2020 Category: Physics Authors: Watanabe Y, Maeyama T, Mochizuki A, Mizukami S, Hayashi SI, Terazaki T, Muraishi H, Takei H, Gomi T, Shimono T Tags: Phys Med Biol Source Type: research

Deep learning on mammary glands distribution for architectural distortion detection in digital breast tomosynthesis.
Abstract Computer aided detection (CADe) for breast lesion can provide an important reference for radiologists in breast cancer screening. Architectural distortion (AD) is a type of breast lesion that is difficult to detect. A majority of CADe methods focus on detecting the radial pattern, which is a main characteristic of typical ADs. However, a few atypical ADs do not exhibit such a pattern. To improve the performance of CADe for typical and atypical ADs, we proposed a deep-learning-based model that used the mammary glands distribution as prior information to detect ADs in digital breast tomosynthesis (DBT). Fir...
Source: Physics in Medicine and Biology - June 2, 2020 Category: Physics Authors: Li Y, He Z, Lu Y, Ma X, Guo Y, Xie Z, Xu Z, Chen W, Chen H Tags: Phys Med Biol Source Type: research

Characterization of the PTW-34089 type 147 mm diameter large-area ionization chamber for use in light-ion beams.
Abstract A newly-designed large-area plane-parallel ionization chamber (of type PTW 34089), denoted BPC150, with a nominal active volume diameter of 147 mm is characterized in this study. Such chambers exhibit benefits compared to smaller chambers in the field of scanned light-ion beam dosimetry because they capture a larger fraction of the laterally-spread beam fragments and ease positioning with respect to small fields. The chamber was characterized in60Co, 200 kV X-ray, proton and carbon ion beams. The chamber-specific beam-quality correction factor kQ,Q0was determined. To investigate the homogeneity of the cha...
Source: Physics in Medicine and Biology - June 1, 2020 Category: Physics Authors: Kuess P, Haupt S, Osorio J, Grevillot L, Fuchs H, Georg D, Palmans H Tags: Phys Med Biol Source Type: research

Challenging the Norm: What Level of Evidence Is Necessary to Adopt Postprostatectomy Hypofractionated Radiation Therapy?
PMID: 32386737 [PubMed - in process] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - May 12, 2020 Category: Physics Authors: Nagar H, Spratt DE Tags: Int J Radiat Oncol Biol Phys Source Type: research

Roadmap for metal nanoparticles in radiation therapy: current status, translational challenges, and future directions.
Ngwa W, Payne JD, Penninckx S, Porcel E, Prise KM, Rabus H, Ridwan SM, Rudek B, Sanche L, Singh B, Smilowitz HM, Sokolov KV, Sridhar S, Stanishevskiy Y, Sung W, Tillement O, Virani NA, Yantasee W, Krishnan S Abstract This roadmap outlines the potential roles of metallic nanoparticles (MNPs) in the field of radiation therapy. MNPs made up of a wide range of materials (from Titanium, Z=22, to Bismuth, Z=83) and a similarly wide spectrum of potential clinical applications, including diagnostic, therapeutic (radiation dose enhancers, hyperthermia inducers, drug delivery vehicles, vaccine adjuvants, photosensitizers, e...
Source: Physics in Medicine and Biology - May 7, 2020 Category: Physics Authors: Schuemann J, Bagley A, Berbeco R, Bromma K, Butterworth KT, Byrne H, Chithrani DB, Cho SH, Cook JR, Favaudon V, Gholami YH, Gargioni E, Hainfeld JF, Hespeels F, Heuskin AC, Ibeh UM, Kuncic Z, Kunjachan S, Lacombe S, Lucas S, Lux F, McMahon SJ, Nevozhay D, Tags: Phys Med Biol Source Type: research

Performance evaluation of a novel multi-pinhole collimator for dopamine transporter SPECT.
This study evaluated a novel MPH collimator specifically designed for dopamine transporter (DAT) SPECT with a triple-head SPECT camera. Count sensitivity was measured with a99mTc point source placed on the lattice points of a 1cm grid covering the whole field-of-view (FOV). Spatial resolution was assessed with a Derenzo type hot rod phantom. An anthropomorphic striatum phantom was scanned with total activity representative of a typical patient scan and different striatum-to-background activity concentration ratios. Recovery of striatum-to-background contrast was assessed by the contrast-recovery-coefficient. Measurements w...
Source: Physics in Medicine and Biology - May 5, 2020 Category: Physics Authors: Tecklenburg K, Forgács A, Apostolova I, Lehnert W, Klutmann S, Csirik J, Garutti E, Buchert R Tags: Phys Med Biol Source Type: research

Quantification of defect contrast in microSPECT imaging of a myocardial phantom.
Abstract Ischemic heart disease remains a significant public health concern, accentuating the importance of basic research and therapeutic studies of small animals in which myocardial changes can be reproducibly detected and quantified. Few or no studies have investigated the performance of microSPECT in quantifying myocardial lesions. We utilized three versions of a multi-compartment phantom containing two left ventricular myocardial compartments (one uniform and one with a transmural 'cold' defect), a ventricular blood pool, and a background compartment, where each version had a different myocardial wall thickne...
Source: Physics in Medicine and Biology - May 5, 2020 Category: Physics Authors: Johnson LC, Guerraty MA, Moore SC, Metzler SD Tags: Phys Med Biol Source Type: research

Artifact removal using a hybrid-domain convolutional neural network for limited-angle computed tomography imaging.
Abstract The suppression of streak artifacts in computed tomography with a limited-angle configuration is challenging. Conventional analytical algorithms, such as filtered backprojection (FBP), are not successful due to incomplete projection data. Moreover, model-based iterative total variation (TV) algorithms effectively reduce small streaks but do not work well at eliminating large streaks. In contrast, FBP mapping networks and deep-learning-based postprocessing networks are outstanding at removing large streak artifacts; however, these methods perform processing in separate domains, and the advantages of multip...
Source: Physics in Medicine and Biology - May 5, 2020 Category: Physics Authors: Zhang Q, Hu Z, Jiang C, Zheng H, Ge Y, Liang D Tags: Phys Med Biol Source Type: research

Deformable image registration of the treatment planning CT with proton radiographies in perspective of adaptive proton therapy.
In conclusion, the choice of detector configuration as well as the amount and the complexity of the considered anatomical changes determine the minimum number of radiographies to be used. PMID: 32365335 [PubMed - as supplied by publisher] (Source: Physics in Medicine and Biology)
Source: Physics in Medicine and Biology - May 4, 2020 Category: Physics Authors: Palaniappan P, Meyer S, Kamp F, Belka C, Riboldi M, Parodi K, Gianoli C Tags: Phys Med Biol Source Type: research

A dual-domain deep learning-based reconstruction method for fully 3D sparse data helical CT.
Abstract Helical CT has been widely used in clinical diagnosis. In this work, we focus on a new prototype of helical CT which equipped with sparsely spaced multidetector and multi-slit collimator (MSC) in the axis direction. This kind systems can not only lower radiation dose, suppress scattering by MSC, but also cut down the manufacturing cost of detector. The major problem to overcome for such a system is the insufficient data for reconstruction. Hence, we propose a deep learning-based function optimization method for this ill-posed inverse problem. By incorporating Radon inverse operator and disentangling each ...
Source: Physics in Medicine and Biology - May 4, 2020 Category: Physics Authors: Zheng A, Gao H, Zhang L, Xing Y Tags: Phys Med Biol Source Type: research

Small animal PET: a review of what we have done and where we are going.
Abstract Small animal research is an essential tool in studying both pharmaceutical biodistributions and disease progression over time. Furthermore, through the rapid development of in vivo imaging technology over the last few decades, small animal imaging (also referred to as preclinical imaging) has become a mainstay for all fields of biologic research and a center point for most preclinical cancer research. Preclinical imaging modalities include optical, MRI and MRS, microCT, small animal PET, ultrasound, and photoacoustic, each with their individual strengths. The strong points of small animal PET are its tran...
Source: Physics in Medicine and Biology - May 1, 2020 Category: Physics Authors: Miyaoka RS, Lehnert A Tags: Phys Med Biol Source Type: research

Generative adversarial network based regularized image reconstruction for PET.
Abstract Positron emission tomography (PET) is an ill-posed inverse problem and suffers high noise due to limited number of detected events. Prior information can be used to improve the quality of reconstructed PET images. Deep neural networks have also been applied to regularized image reconstruction. One method is to use a pretrained denoising neural network to represent the PET image and to perform a constrained maximum likelihood estimation. In this work, we propose to use a generative adversarial network (GAN) to further improve the network performance. We also modify the objective function to include a data-...
Source: Physics in Medicine and Biology - May 1, 2020 Category: Physics Authors: Xie Z, Baikejiang R, Li T, Zhang X, Gong K, Zhang M, Qi W, Asma E, Qi J Tags: Phys Med Biol Source Type: research

Whole gamma imaging: a new concept of PET combined with Compton imaging.
Abstract We proposed a concept of whole gamma imaging (WGI) that utilizes all detectable gamma rays for imaging. An additional detector ring, which is used as the scatterer, is inserted in the field-of-view of a PET ring so that single gamma rays can be detected by the Compton imaging method. In particular, for the non-pure positron emitters which emit an additional gamma ray almost at the same time, triple gamma imaging will be enabled; localization on each line-of-response (LOR) is possible by using the Compton cone of the additional gamma ray. We developed a prototype to show a proof of the WGI concept. The dia...
Source: Physics in Medicine and Biology - April 29, 2020 Category: Physics Authors: Yoshida E, Tashima H, Nagatsu K, Tsuji A, Kamada K, Parodi K, Yamaya T Tags: Phys Med Biol Source Type: research

Multi-level feature aggregation network for instrument identification of endoscopic image.
This study proposes a novel multilevel feature-aggregated deep convolutional neural network (MLFA-Net) for identifying surgical instruments in endoscopic images. First, a global feature augmentation layer is created on the top layer of the backbone to improve the localization ability of object identification by boosting the high-level semantic information to the feature flow network. Second, a modified interaction path of cross-channel features is proposed to increase the nonlinear combination of features in the same level and improve the efficiency of information propagation. Third, a multiview fusion branch of features i...
Source: Physics in Medicine and Biology - April 28, 2020 Category: Physics Authors: Chu Y, Yang XM, Li H, Ai D, Ding Y, Fan J, Song H, Yang J Tags: Phys Med Biol Source Type: research

Image quality of list-mode proton imaging without front trackers.
c I, Seco J Abstract List mode proton imaging relies on accurate reconstruction of the proton most likely path (MLP) through the patient. This typically requires two sets of position sensitive detector systems, one upstream (front) and one downstream (rear) of the patient. However, for a clinical implementation it can be preferable to omit the front trackers (single-sided proton imaging). For such a system, the MLP can be computed from information available through the beam delivery system and the remaining rear tracker set. In this work, we use Monte Carlo simulations to compare a conventional double-sided (using...
Source: Physics in Medicine and Biology - April 28, 2020 Category: Physics Authors: Sølie JRR, Volz L, Pettersen HESES, Piersimoni P, Odland OH, Roehrich D, Helstrup H, Peitzmann T, Ullaland K, Varga-Kofarago M, Mehendale S, Grøttvik OS, Eikeland VN, Meric I, Seco J Tags: Phys Med Biol Source Type: research

Body-size-dependent phantom library constructed from ICRP mesh-type reference computational phantoms.
Abstract Recently, ICRP Task Group 103 developed new mesh-type reference computational phantoms (MRCPs) for the adult male and female by converting the current voxel-type reference computational phantoms (VRCPs) of ICRPPublication 110into a high-quality/fidelity mesh format. Utilizing the great deformability/flexibility of the MRCPs compared with the VRCPs, in the present study, we established a body-size-dependent phantom library by modifying the MRCPs. The established library includes 108 adult male and 104 adult female phantoms in different standing heights and body weights, covering most body sizes representat...
Source: Physics in Medicine and Biology - April 28, 2020 Category: Physics Authors: Choi C, Yeom YS, Lee H, Han H, Shin B, Nguyen TT, Kim CH Tags: Phys Med Biol Source Type: research

Time-resolved dosimetry for validation of 4D dose calculation in PBS proton therapy.
In this study a novel approach of time-resolved dosimetry using five pinpoint ionization chambers (IC) embedded in an anthropomorphic dynamic phantom was employed and validated against beam delivery details. Beam intensity variations as well as beam delivery time-structure were well reflected with an accuracy comparable to the temporal resolution of the IC measurements. The 4D dosimetry approach was further applied for benchmarking 4D-DC implemented in the RayStation 6.99 treatment planning system. The agreement between computed values and measurements was investigated for: (i) partial doses based on individual breathing p...
Source: Physics in Medicine and Biology - April 27, 2020 Category: Physics Authors: Kostiukhina N, Palmans H, Stock M, Knopf AC, Georg D, Knaeusl B Tags: Phys Med Biol Source Type: research

Quantitative imaging of coronary flows using 3D ultrafast doppler coronary angiography.
In this study, we introduce 3-D Ultrafast Doppler Coronary Angiography (3-D UDCA), an ultrasound-based method to assess coronary blood flows in three-dimensions at high volume-rate and in one single heartbeat. We demonstrate that 3-D UDCA can visualize the coronary vasculature with high temporal and spatial resolution and quantify the absolute flow. The feasibility of the technique was demonstrated in an open-chest swine model. The flow rate of the left-anterior descending artery (LAD) assessed by 3-D UDCA was reconstructed successfully at the early diastolic and late diastolic phases and was in good agreement with an inva...
Source: Physics in Medicine and Biology - April 27, 2020 Category: Physics Authors: Correia M, Maresca D, Goudot G, Villemain O, Bize A, Sambin L, Tanter M, Ghaleh B, Pernot M Tags: Phys Med Biol Source Type: research

Impact of Gaussian uncertainty assumptions on probabilistic optimization in particle therapy.
Abstract Range and setup uncertainties in charged particle therapy may induce a discrepancy between planned and delivered dose. Countermeasures based on probabilistic optimization assume a Gaussian probability density to model the underlying range and setup error. While this assumption is generally taken for granted, this work explicitly investigates dosimetric consequences if the actual errors obey a different probability density function (PDF) over the course of treatment than the one used during probabilistic treatment plan optimization. Discrete random sampling was performed for conventionally and probabilisti...
Source: Physics in Medicine and Biology - April 27, 2020 Category: Physics Authors: Wieser HP, Karger CP, Wahl N, Bangert M Tags: Phys Med Biol Source Type: research