Breathing Phases Research Articles

MO-FG-BRA-04: A Novel Time Weighted Density Correction for Stereotactic Lung Radiotherapy: A Phantom Study

Purpose: Conventional treatment plans for lung radiotherapy are created using either the free breathing (FB) scheme which represents the tumor at an arbitrary breathing phase of the patient's respiratory cycle, or the average computed tomography (ACT) intensity projection over 10-binned phases. Neither method is entirely accurate because of the absence of time dependence of tumor movement. In the present “Hybrid” method, the HU of tumor in 3D space is determined by relative weighting of the HU of the tumor and lung in proportion to the time they spend at that location during the entire breathing cycle. Methods: A Quasar respiratory motion phantom was employed to simulate lung tumor movement. Utilizing 4DCT image scans, volumetric modulated arc therapy (VMAT) plans were generated for three treatment planning scenarios which included conventional FB and ACT schemes, along with a third alternative Hybrid approach. Our internal target volume (ITV) hybrid structure was created using Boolean operation in Eclipse (ver. 11) treatment planning system, where independent sub-regions created by the gross tumor volume (GTV) overlap from the 10 motion phases were each assigned a time weighted CT value. The dose-volume-histograms (DVH) for each scheme were compared and analyzed. Results: Using our hybrid technique, we have demonstrated a reduction of 1.9% – 3.4% in total monitor units with respect to conventional treatment planning strategies, along with a 6 fold improvement in high dose spillage over the FB plan. The higher density ACT and Hybrid schemes also produced a slight enhancement in target conformity and reduction in low dose spillage. Conclusion: All treatment plans created in this study exceeded RTOG protocol criteria. Our results determine the free breathing approach yields an inaccurate account of the target treatment density. A significant decrease in unnecessary lung irradiation can be achieved by implementing Hybrid HU method with ACT method second best.

Differences in displacement of the proximal and distal ends of mid-upper thoracic esophageal squamous cell carcinoma.

In the present study, clips were used as markers to evaluate displacement differences between proximal and distal ends of esophageal tumors and to test whether their internal target volume (ITV) margins should be determined separately. A total of 23 patients with mid-upper thoracic esophageal squamous-cell carcinoma, a tumor length of ≤8 cm and an esophageal lumen suitable for endoscopic ultrasonography were recruited for the present study. Clips were implanted endoscopically at the proximal and distal ends of the esophageal tumor (upper and lower clips). In a further exploratory study on 16 of the patients, a third clip was placed at the distal esophagus 2 cm above the gastro-esophageal junction (GEJ) (cardiac clip). The clips were contoured for all 10 phases of the four-dimensional computed tomography and the maximum displacements of the clip centroids among different breathing phases in left-right (LR), superior-inferior (SI) and anterior-posterior (AP) directions were marked as x, y and z, respectively. The ITV margins that covered 95% of the LR, SI and AP motion were 2.89, 5.00 and 2.36 mm, respectively. Axial displacement (y) was greater than radial displacement (x, z; P<0.05). It was also revealed that LR(x), SI(y) and AP(z) displacement of cardiac clips was greater than that of upper or lower clips (P<0.05). Differences in the axial and radial displacement of the upper and lower clips indicated that axial and radial ITV margins should be determined separately. However, further study is required on patients in whom the distal tumor end is located in proximity to the GEJ.

Evaluation of the usefulness of modified biological fingerprints in chest radiographs for patient recognition and identification.

We have been developing an image-searching method to identify misfiled images in a PACS server. Developing new biological fingerprints (BFs) that would reduce the influence of differences in positioning and breathing phases to improve the performance of recognition is desirable. In our previous studies, the whole lung field (WLF) that included the shadows of the body and lungs was affected by differences in positioning and/or breathing phases. In this study, we showed the usefulness of a circumscribed lung with a rectangular region of interest and the upper half of a chest radiograph as modified BFs. We used 200 images as hypothetically misfiled images. The cross-correlation identifies the resemblance between the BFs in the misfiled images and the corresponding BFs in the database images. The modified BFs indicated better results than did WLF in a receiver operating characteristic analysis; therefore, they could be used as identifiers for patient recognition and identification.

Postinspiratory complex: a third excitatory respiratory oscillator

Mammalian respiration consists of three phases: (1) inspiration, (2) an early phase of expiration, postinspiration, and (3) a late phase of expiration. Two excitatory oscillators have been proposed for the generation of inspiration and active expiration, a conditional expiration that occurs during the late expiratory phase. However, the cellular and circuit mechanisms underlying the generation of postinspiration are largely unknown. Here we describe a third, previously undiscovered excitatory rhythm generator, the Postinspiratory Complex, or PIC, located immediately caudal to the facial nucleus and just medial and dorsal to the rostral‐most portion of the nucleus ambiguus. In this study a variety of in vitro and in vivo approaches are employed to demonstrate that this rhythmogenic kernel generates activity in the postinspiratory phase. Immunohistochemical and optogenetic techniques are utilized to reveal that PIC neurons co‐express acetylcholine and glutamate. Differential responses to neuromodulators and a distinct anatomical location distinguish the PIC from other described respiratory oscillators. Inhibitory interactions between this rhythmogenic network and the preBötzinger Complex, the network responsible for generating inspiration, establish the relative timing, but are not responsible for the generation of the burst underlying inspiratory and postinspiratory activity. Light stimulation of cholinergic PIC neurons in Chat‐cre:Ai27 mice evokes postinspiratory vagal activity in vivo that can reset the inspiratory rhythm. We therefore propose that the three phases of mammalian breathing are generated by three excitatory rhythmogenic medullary networks that are coordinated by inhibitory mechanisms.Support or Funding InformationNIH NS087828‐01NIH HL107084‐01

Mixed-mode oscillations and population bursting in the pre-Bötzinger complex.

This study focuses on computational and theoretical investigations of neuronal activity arising in the pre-Bötzinger complex (pre-BötC), a medullary region generating the inspiratory phase of breathing in mammals. A progressive increase of neuronal excitability in medullary slices containing the pre-BötC produces mixed-mode oscillations (MMOs) characterized by large amplitude population bursts alternating with a series of small amplitude bursts. Using two different computational models, we demonstrate that MMOs emerge within a heterogeneous excitatory neural network because of progressive neuronal recruitment and synchronization. The MMO pattern depends on the distributed neuronal excitability, the density and weights of network interconnections, and the cellular properties underlying endogenous bursting. Critically, the latter should provide a reduction of spiking frequency within neuronal bursts with increasing burst frequency and a dependence of the after-burst recovery period on burst amplitude. Our study highlights a novel mechanism by which heterogeneity naturally leads to complex dynamics in rhythmic neuronal populations.

Nonlocal Means Denoising of Self-Gated and k-Space Sorted 4-Dimensional Magnetic Resonance Imaging Using Block-Matching and 3-Dimensional Filtering: Implications for Pancreatic Tumor Registration and Segmentation

Todenoise self-gated k-space sorted 4-dimensional magnetic resonance imaging (SG-KS-4D-MRI) by applying a nonlocal means denoising filter, block-matching and 3-dimensional filtering (BM3D), to test its impact on the accuracy of 4D image deformable registration and automated tumor segmentation for pancreatic cancer patients. Nine patients with pancreatic cancer and abdominal SG-KS-4D-MRI were included in the study. Block-matching and 3D filtering was adapted to search in the axial slices/frames adjacent to the reference image patch in the spatial and temporal domains. The patches with high similarity to the reference patch were used to collectively denoise the 4D-MRI image. The pancreas tumor was manually contoured on the first end-of-exhalation phase for both the raw and the denoised 4D-MRI. B-spline deformable registration was applied to the subsequent phases for contour propagation. The consistency of tumor volume defined by the standard deviation of gross tumor volumes from 10 breathing phases (σ_GTV), tumor motion trajectories in 3 cardinal motion planes, 4D-MRI imaging noise, and image contrast-to-noise ratio were compared between the raw and denoised groups. Block-matching and 3D filtering visually and quantitatively reduced image noise by 52% and improved image contrast-to-noise ratio by 56%, without compromising soft tissue edge definitions. Automatic tumor segmentation is statistically more consistent on the denoised 4D-MRI (σ_GTV=0.6cm(3)) than on the raw 4D-MRI (σ_GTV=0.8cm(3)). Tumor end-of-exhalation location is also more reproducible on the denoised 4D-MRI than on the raw 4D-MRI in all 3 cardinal motion planes. Block-matching and 3D filtering can significantly reduce random image noise while maintaining structural features in the SG-KS-4D-MRI datasets. In this study of pancreatic tumor segmentation, automatic segmentation of GTV in the registered image sets is shown to be more consistent on the denoised 4D-MRI than on the raw 4D-MRI.

Quantification of respiration-induced esophageal tumor motion using fiducial markers and four-dimensional computed tomography

Background and purposeRespiration-induced tumor motion is an important geometrical uncertainty in esophageal cancer radiation therapy. The aim of this study was to quantify this motion using fiducial markers and four-dimensional computed tomography (4DCT). Materials and methodsTwenty esophageal cancer patients underwent endoscopy-guided marker implantation in the tumor volume and 4DCT acquisition. The 4DCT data were sorted into 10 breathing phases and the end-of-inhalation phase was selected as reference. We quantified for each visible marker (n=60) the motion in each phase and derived the peak-to-peak motion magnitude throughout the breathing cycle. The motion was quantified and analyzed for four different regions and in three orthogonal directions. ResultsThe median(interquartile range) of the peak-to-peak magnitudes of the respiration-induced marker motion (left–right/anterior–posterior/cranial–caudal) was 1.5(0.5)/1.6(0.5)/2.9(1.4) mm for the proximal esophagus (n=6), 1.5(1.4)/1.4(1.3)/3.7(2.6) mm for the middle esophagus (n=12), 2.6(1.3)/3.3(1.8)/5.4(2.9) mm for the distal esophagus (n=25), and 3.7(2.1)/5.3(1.8)/8.2(3.1) mm for the proximal stomach (n=17). ConclusionsThe variations in the results between the three directions, four regions, and patients suggest the need of individualized region-dependent anisotropic internal margins. Therefore, we recommend using markers with 4DCT to patient-specifically adapt the internal target volume (ITV). Without 4DCT, 3DCTs at the end-of-inhalation and end-of-exhalation phases could be alternatively applied for ITV individualization.

Fabrication of ordered honeycomb amphiphobic films with extremely low fluorine content

A series of poly(methyl methacrylate)-block-poly(perfluoroalkyl ethyl acrylate) (PMMA-b-PFAEA) with various fluorine content were employed to fabricate honeycomb ordered films via breath figure strategy. The influences of temperature, concentration, relative humidity, fluorine content on the morphology of porous films were investigated. Wetting behavior including hydrophobic property and wetting state of the films was studied. High surface roughness from the porous structure and low surface free energy from the increasing PFAEA fraction led to the enhancement of hydrophobicity. Additionally, fabrication of porous films by the mixture of PMMA and PMMA-b-PFAEA was investigated. Ordered porous film with excellent hydrophobicity and oleophobicity was obtained with only 7wt% of PMMA-b-PFAEA by simultaneous processes of breath figure mechanism and phase separation. This work facilitates our further comprehension of the mechanism of breath figure and contributes to the fabrication of porous film from fluorinated copolymers. Meanwhile, it opens a new route to prepare films possessing excellent hydrophobicity and oleophobicity with extremely low fluorine content.

Whole heart free breathing phase sensitive inversion recovery MRI integrated with iterative self navigation for 100% scan efficiency; a first patient study

Background Phase Sensitive Inversion Recovery (PSIR) [1] allows for the visualization of myocardial scars using late gadolinium enhancement (LGE), ensuring robustness with respect to sequence timing. 3D whole-heart PSIR has been integrated with diaphragmatic navigator-gating (NAV) [2] to compensate for respiratory motion. However, both NAV and the need for two different datasets to be acquired (IR and reference) lead to a prohibitively long scanning time. Thus, integrating 1D respiratory Self-Navigation (SN) [3] with 3D-PSIR to obtain 100% scan efficiency is desirable. Unfortunately, signal and contrast variations between the IR and the reference dataset pose a major challenge. Here, we hypothesized that a recently introduced contrast independent iterative approach to 1D SN (IT-SN) [4] effectively suppresses respiratory motion in 3D-PSIR acquisitions.

Motion and volumetric change as demonstrated by 4DCT: The effects of abdominal compression on the GTV, lungs, and heart in lung cancer patients

PurposeLung tumors move during respiration, complicating radiation therapy. The abdominal compression plate (ACP) is thought to reduce respiratory motion. This study quantifies ACP efficacy on respiratory-induced motion by using 4-dimensional computed tomography to evaluate volume and displacement changes of the heart, lungs, and tumor with and without ACP. Methods and materialsLung cancer patients (n = 17) received 4-dimensional computed tomography simulations (10 computed tomography scans from 0% to 90% breathing phases) with and without ACP under maximally tolerated diaphragmatic pressure. Gross tumor volume (GTV), heart, and lungs were contoured in treatment planning software for each phase. Structures were exported for analysis. For each phase, with and without ACP, tumor and organ absolute centroid range of motion and volume were calculated. ResultsACP did not significantly affect GTV, heart, or lung motion on the sample as a whole, but instead demonstrated patient-specific results. ACP reduced GTV motion in 3 (17.6%; 3 upper lobe tumors) by 2.9 mm (P < .01), increased motion in 5 (29.4%; 3 upper lobe tumors, 1 middle lobe, 1 lower lobe) by 1.9 mm (P < .03), and did not significantly change 9. Of the 3 patients exhibiting significantly decreased GTV motion, GTV, heart, and lung range of motion was 7.4 mm, 11.8 mm, and 11.9 mm, respectively, without compression and 4.5 mm, 8.4 mm, and 10.9 mm, respectively, with compression. Averaged across the sample, ACP did not exhibit any axis-specific effect. ConclusionsACP efficacy was patient-specific, possibly because of pre-existing factors including chronic obstructive pulmonary disease severity, chest wall elasticity, tumor location, and patient comfort. Tumor lobe location does not predetermine compression efficacy; therefore, patients should be simulated with and without ACP, regardless of tumor location. GTV motion seems most important in determining suitability for compression. Alternative motion control should be considered in patients not benefited by compression. In patients who benefited, ACP may enhance tumor coverage while minimizing toxicity. Larger scale studies are necessary for definitive treatment recommendations.

Four Dimensional Magnetic Resonance Imaging With 3D Radial Sampling and Self-gating Based K-space Sorting: Early Clinical Experience on Pancreatic Cancer Patients

Dynamic magnetic resonance imaging (MRI) has been used to characterize internal organ motion, but real-time acquisition has been limited to 2 dimensions (2D). Methods have been developed to reconstruct four dimensional MRI (4D-MRI) based on rebinning time-stamped 2D images or 2D K-space data. These methods suffer from anisotropic resolution and rebinning artifacts. We developed a 4D-MRI technique using 3D radial sampling and self-gating based K-space sorting (SG-KS-4D-MRI) to overcome these limitations, and applied it to study the target motion of pancreatic cancer patients. Ten patients were imaged during free breathing using 4D-CT, cine 2D-MRI and the SG-KS-4D-MRI method, which is an 8-minute spoiled gradient recalled echo (GRE) sequence with 3D radial-sampling K-space projections and 1D projection based self-gating. Tumor volumes were drawn at the end of exhalation phases in the SG-KS-4D-MRI and 4D-CT for each patient, and then mapped to the other phases using deformable registration with B-spline algorithm. Tumor volumes and motion trajectories were compared. An isotropic resolution of 1.6 mm was achieved in the SG-KS-4D-MRI images, which showed superior soft tissue contrast to 4D-CT and were free of visible rebinning artifacts. The tumor motion trajectory cross-correlations between SG-KS-4D-MRI and cine 2D-MRI directions in superior-inferior (SI), anterior-posterior (AP) and medial-lateral (ML) directions were 0.93 ± 0.03, 0.83 ± 0.10, and 0.74 ± 0.18, respectively. The tumor motion trajectory cross-correlations between the SG-KS-4D-MRI and 4D-CT in SI, AP and ML were 0.91 ± 0.06, 0.72 ± 0.18, and 0.44 ± 0.24, respectively. The average motion amplitude differences (Ddiff) between SG-KS-4D-MRI and cine 2D-MRI in SI, AP, and ML directions were 0.83 ± 0.52, 0.40 ± 0.17, and 0.48 ± 0.24 mm. The Ddiff between SG-KS-4D-MRI and 4D-CT in SI, AP, and ML directions were 1.09 ± 0.43, 0.53 ± 0.24, and 0.47 ± 0.26 mm, respectively. The average standard deviations of the GTV volumes (GTV_σ) calculated from each of the ten breathing phases were 0.8 cm3 (SG-KS-4D-MRI) and 1.0 cm3 (4D-CT), P = .004, indicating a statistically significant difference between the two imaging modalities. A novel 4D-MRI imaging sequence, SG-KS-4D-MRI, was used to evaluate target motion for free breathing pancreatic cancer patients. Pancreatic motion trajectories agreed well with 4D-CT and cine 2D-MRI data in the SI and AP directions, but agreement was limited in the ML direction, where image pixel size and displacements are of similar size. Use of SG-KS-4D-MRI results in improved spatial resolution, voxel isotropy, and gives an average motion pattern over an extended period of time; SG-KS-4D-MRI also results in statistically more consistent tumor volume definition across the ten breathing phases.

Which CT Set for Lung SBRT Planning: The Effect of Varying Lung Density on Monte Carlo Dose Calculation

Free-breathing (FB) and average CTs are common CT images used for SBRT lung planning. The FB CT, a fast 3D scan, consists of random snap shots at different breathing phases for different CT bed positions. The average CT, often created as a mean intensity projection from a slow 4D CT, represents a time-averaged anatomy. While the average CT has been shown to be advantageous for GTV contouring and target localization, both are believed to be equivalent for dose calculation with conventional algorithms (pencil beam, convolution superposition). Since previous studies demonstrated considerable MC dose dependence on varying lung densities, whether in phantoms or between patients with different lung densities, we aimed to study the lung density variation between FB and average CTs, and its effect on MC dose calculation increasingly used in lung SBRT planning. With IRB approval, 10 previously-treated lung SBRT patients were randomly chosen. For each patient, both a FB CT and an 8-phase 4D CT were acquired. The 4D CT was used for contouring an ITV while the FB CT was used for treatment planning with dynamic conformal arcs in clinical treatments. Lungs were contoured on the FB CT, on each phase of the 4D CT, and on an average CT created from the 4D CT. Lung density was compared for each patient among these 10 different data sets. Dose distribution was calculated with MC (iPlan, BrainLab) on FB and average CTs for dose comparison using D5, Dmean and D95 of PTV and GTV, as well as RTOG 0813 protocol compliance. Wilcoxon’s signed rank test was used. For the 10 studied patients, the median (range) of the minimum, mean, and maximum lung density from the 4D CT was 0.26 (0.10∼0.34), 0.31 (0.12∼0.43), 0.35 (0.22∼0.51) g/cc, respectively. Using the mean lung density from the 4D CT as the gold standard, the median (range) deviation of that on the FB and average CT was -0.03 (-0.09∼0.02) and 0.00 (-0.01∼0.01) g/cc, respectively. For the PTV, the median (range) D5, Dmean and D95 percent difference between the FB and average CT dose calculation was -1.9 (-5.1∼1.2%), -0.2 (-1.1∼0.4%) and -1.1 (-4.3∼0.7%), and for the GTV, -1.0 (-2.9∼0.8%), -0.2 (-0.4∼0.3%) and -0.8 (-2.4∼0.5%), respectively. There was no dose index difference that was statistically significant (P< 0.05) for the studied population. RTOG compliance was not different between the two CT sets for any patient. Lung density on the average CT accurately represents the mean density from the 4D CT. Varying density differences were observed between the average and FB CTs, hence leading to varying dosimetric differences in MC dose calculated. However, for the 10 studied patients, the dosimetric differences were not statistically significant. This suggests that negligible difference between FB and average CT is expected for MC calculation, similar to what previously believed true for conventional dose algorithms.

A Touchless Tool to Improve Gated Radiation Therapy: Thermal Camera Based Breathing Phase Monitoring

A Touchless Tool to Improve Gated Radiation Therapy: Thermal Camera Based Breathing Phase Monitoring

Inferior vena cava collapsibility loses correlation with internal jugular vein collapsibility during increased thoracic or intra-abdominal pressure.

Point-of-care ultrasound evaluates inferior vena cava (IVC) and internal jugular vein (IJV) measurements to estimate intravascular volume status. The reliability of the IVC and IJV collapsibility index during increased thoracic or intra-abdominal pressure remains unclear. Three phases of sonographic scanning were performed: spontaneous breathing phase, increased thoracic pressure phase via positive pressure ventilation (PPV) phase, and increased intra-abdominal pressure (IAP) phase via laparoscopic insufflation to 15mmHg. IVC measurements were done at 1-2cm below the diaphragm and IJV measurements were done at the level of the cricoid cartilage during a complete respiratory cycle. Collapsibility index was calculated by (max diameter-min diameter)/max diameter×100%. Chi square, t test, correlation procedure (CORR) and Fisher's exact analyses were completed. A total of 144 scans of the IVC and IJV were completed in 16 patients who underwent laparoscopic surgery. Mean age was 46±15years, with 75% female and 69% African-American. IVC and IJV collapsibility correlated in the setting of spontaneous breathing (r (2)=0.86, p<0.01). IVC collapsibility had no correlation with the IJV in the setting of PPV (r (2)=0.21, p=0.52) or IAP (r (2)=0.26, p=0.42). Maximal IVC diameter was significantly smaller during increased IAP (16.5mm±4.9) compared to spontaneous breathing (20.6mm±4.8, p=0.04) and PPV (21.8mm±5.6, p=0.01). IJV and IVC collapsibility correlated during spontaneous breathing but there was no statistically significant correlation during increased thoracic or intra-abdominal pressure. Increased intra-abdominal pressure was associated with a significant smaller maximal IVC diameter and cautions the reliability of IVC diameter in clinical settings that are associated with intra-abdominal hypertension or abdominal compartment syndrome.

Studying respiratory rhythm generation in a developing bird: Hatching a new experimental model using the classic in vitro brainstem-spinal cord preparation

It has been more than thirty years since the in vitro brainstem-spinal cord preparation was first presented as a method to study automatic breathing behaviors in the neonatal rat. This straightforward preparation has led to an incredible burst of information about the location and coordination of several spontaneously active microcircuits that form the ventrolateral respiratory network of the brainstem. Despite these advances, our knowledge of the mechanisms that regulate central breathing behaviors is still incomplete. Investigations into the nature of spontaneous breathing rhythmicity have almost exclusively focused on mammals, and there is a need for comparative experimental models to evaluate several unresolved issues from a different perspective. With this in mind, we sought to develop a new avian in vitro model with the long term goal to better understand questions associated with the ontogeny of respiratory rhythm generation, neuroplasticity, and whether multiple, independent oscillators drive the major phases of breathing. The fact that birds develop in ovo provides unparalleled access to central neuronal networks throughout the prenatal period – from embryo to hatchling – that are free from confounding interactions with mother. Previous studies using in vitro avian models have been strictly limited to the early embryonic period. Consequently, the details and even the presence of brainstem derived breathing-related rhythmogenesis in birds have never been described. In the present study, we used the altricial zebra finch (Taeniopygia guttata) and show robust spontaneous motor outflow through cranial motor nerve IX, which is first detectable on embryonic day four and continues through prenatal and early postnatal development without interruption. We also show that brainstem oscillations change dramatically over the course of prenatal development, sometimes within hours, which suggests rapid maturational modifications in growth and connectivity. We propose that this experimental preparation will be useful for a variety of studies aimed at testing the biophysical and synaptic properties of neurons that participate in the unique spatiotemporal patterns of avian breathing behaviors, especially in the context of early development.

Computational fluid-structure interaction simulation of airflow in the human upper airway

Obstructive sleep apnoea syndrome (OSAS) is a breathing disorder in sleep developed as a consequence of upper airway anatomical characteristics and sleep-related muscle relaxation. Fluid-structure interaction (FSI) simulation was adopted to explain the mechanism of pharyngeal collapse and snoring. The focus was put on the velopharyngeal region where the greatest level of upper airway compliance was estimated to occur. The velopharyngeal tissue was considered in a way that ensures proper boundary conditions, at the regions where the tissue adheres to the bone structures. The soft palate with uvula was not cut out from the surrounding tissue and considered as an isolated structure. Both, soft palate flutter as well as airway narrowing have been obtained by 3D FSI simulations which can be considered as a step forward to explain snoring and eventual occlusion. It was found out that during the inspiratory phase of breathing, at given elastic properties of the tissue and without taking gravity into consideration, velopharyngeal narrowing due to negative suction pressure occurs. Furthermore, soft palate flutter as the main attribute of snoring was predicted during the expiratory phase of breathing. The evaluated flutter frequency of 17.8Hz is in close correlation with the frequency of explosive peaks of sound that are produced in palatal snoring in inspiratory phase, as reported in literature.

Four-Dimensional Magnetic Resonance Imaging With 3-Dimensional Radial Sampling and Self-Gating–Based K-Space Sorting: Early Clinical Experience on Pancreatic Cancer Patients

To apply a novel self-gating k-space sorted 4-dimensional MRI (SG-KS-4D-MRI) method to overcome limitations due to anisotropic resolution and rebinning artifacts and to monitor pancreatic tumor motion. Ten patients were imaged using 4D-CT, cine 2-dimensional MRI (2D-MRI), and the SG-KS-4D-MRI, which is a spoiled gradient recalled echo sequence with 3-dimensional radial-sampling k-space projections and 1-dimensional projection-based self-gating. Tumor volumes were defined on all phases in both 4D-MRI and 4D-CT and then compared. An isotropic resolution of 1.56 mm was achieved in the SG-KS-4D-MRI images, which showed superior soft-tissue contrast to 4D-CT and appeared to be free of stitching artifacts. The tumor motion trajectory cross-correlations (mean ± SD) between SG-KS-4D-MRI and cine 2D-MRI in superior-inferior, anterior-posterior, and medial-lateral directions were 0.93 ± 0.03, 0.83 ± 0.10, and 0.74 ± 0.18, respectively. The tumor motion trajectories cross-correlations between SG-KS-4D-MRI and 4D-CT in superior-inferior, anterior-posterior, and medial-lateral directions were 0.91 ± 0.06, 0.72 ± 0.16, and 0.44 ± 0.24, respectively. The average standard deviation of gross tumor volume calculated from the 10 breathing phases was 0.81 cm(3) and 1.02 cm(3) for SG-KS-4D-MRI and 4D-CT, respectively (P=.012). A novel SG-KS-4D-MRI acquisition method capable of reconstructing rebinning artifact-free, high-resolution 4D-MRI images was used to quantify pancreas tumor motion. The resultant pancreatic tumor motion trajectories agreed well with 2D-cine-MRI and 4D-CT. The pancreatic tumor volumes shown in the different phases for the SG-KS-4D-MRI were statistically significantly more consistent than those in the 4D-CT.

Patterns, dynamics and phase transitions in Ising ferromagnet driven by propagating magnetic field wave

The nonequilibrium behaviours of kinetic Ising ferromagnet driven by a propagating magnetic field wave have been studied by Monte Carlo simulation. Two types of propagating magnetic field waves are used here. Namely, the plane wave and the spherical wave. For plane propagating wave passing through the Ising ferromagnet, system undergoes a phase transition from a pinned phase to a propagating phase, as the temperature increases. The transition temperature is found to depend on the amplitude of the propagating magnetic field. A phase boundary is drawn in the plane described by the temperature of the system and amplitude of the propagating field. On the other hand, the nonequilibrium behaviours shown by the Ising ferromagnet driven by spherical magnetic field wave, are different. Here, the system exists in three different dynamical phases. The low temperature pinned phase, the intermediate temperature centrally localised breathing phase and the high temperature extended spreading phase. Here also, the transition temperatures are observed to depend upon the amplitude of the propagating magnetic field wave. The phase boundaries are drawn in the plane represented by temperature of the system and the amplitude of the propagating magnetic field wave. The two boundaries merge at the Onsager value of equilibrium critical temperature in the limit of vanishingly small amplitude of the propagating magnetic field. This article is mainly a review of earlier works and is based on the invited lecture delivered in the conference STATPHYSKOLKATAVIII, held at SNBNCBS, Kolkata, India in December 1-5, 2014. This article is dedicated to Prof. H. Nishimori on the occasion of his 60th birthday.

SU‐E‐T‐151: Breathing Synchronized Delivery (BSD) Planning for RapicArc Treatment

Purpose:To propose a workflow for breathing synchronized delivery (BSD) planning for RapicArc treatment.Methods:The workflow includes three stages: screening/simulation, planning, and delivery. In the screening/simulation stage, a 4D CT with the corresponding breathing pattern is acquired for each of the selected patients, who are able to follow their own breathing pattern. In the planning stage, one breathing phase is chosen as the reference, and contours are delineated on the reference image. Deformation maps to other phases are performed along with contour propagation. Based on the control points of the initial 3D plan for the reference phase and the respiration trace, the correlation with respiration phases, the leaf sequence and gantry angles is determined. The beamlet matrices are calculated with the corresponding breathing phase and deformed to the reference phase. Using the 4D dose evaluation tool and the original 3D plan DVHs criteria, the leaf sequence is further optimized to meet the planning objectives and the machine constraints. In the delivery stage, the patients are instructed to follow the programmed breathing patterns of their own, and all other parts are the same as the conventional Rapid‐Arc delivery.Results:Our plan analysis is based on comparison of the 3D plan with a static target (SD), 3D plan with motion delivery (MD), and the BSD plan. Cyclic motion of range 0 cm to 3 cm was simulated for phantoms and lung CT. The gain of the BSD plan over MD is significant and concordant for both simulation and lung 4DCT, indicating the benefits of 4D planning.Conclusion:Our study shows that the BSD plan can approach the SD plan quality. However, such BSD scheme relies on the patient being able to follow the same breathing curve that is used in the planning stage during radiation delivery.Funded by Varian Medical Systems.

SU‐E‐J‐153: Reconstructing 4D Cone Beam CT Images for Clinical QA of Lung SABR Treatments

Purpose:To verify that the planned Primary Target Volume (PTV) and Internal Gross Tumor Volume (IGTV) fully enclose a moving lung tumor volume as visualized on a pre‐SABR treatment verification 4D Cone Beam CT.Methods:Daily 3DCBCT image sets were acquired immediately prior to treatment for 10 SABR lung patients using the on‐board imaging system integrated into a Varian TrueBeam (v1.6: no 4DCBCT module available). Respiratory information was acquired during the scan using the Varian RPM system. The CBCT projections were sorted into 8 bins offline, both by breathing phase and amplitude, using in‐house software. An iterative algorithm based on total variation minimization, implemented in the open source reconstruction toolkit (RTK), was used to reconstruct the binned projections into 4DCBCT images. The relative tumor motion was quantified by tracking the centroid of the tumor volume from each 4DCBCT image. Following CT‐CBCT registration, the planning CT volumes were compared to the location of the CBCT tumor volume as it moves along its breathing trajectory. An overlap metric quantified the ability of the planned PTV and IGTV to contain the tumor volume at treatment.Results:The 4DCBCT reconstructed images visibly show the tumor motion. The mean overlap between the planned PTV (IGTV) and the 4DCBCT tumor volumes was 100% (94%), with an uncertainty of 5% from the 4DCBCT tumor volume contours. Examination of the tumor motion and overlap metric verify that the IGTV drawn at the planning stage is a good representation of the tumor location at treatment.Conclusion:It is difficult to compare GTV volumes from a 4DCBCT and a planning CT due to image quality differences. However, it was possible to conclude the GTV remained within the PTV 100% of the time thus giving the treatment staff confidence that SABR lung treatements are being delivered accurately.