Respiratory Motion Patterns Research Articles

Remote Respiratory and Cardiac Motion Patterns Separation with 4D Imaging Radars.

Radar-based noncontact physiological signals monitoring is meaningful for daily health monitoring, post-disaster rescue, and public security. This paper focuses on the theoretical and experimental study of noncontact respiratory and cardiac motion signals separation employing remote sensing by a four-dimensional (4D) imaging radar. To adaptively separate respiratory and cardiac motion patterns, we propose a variational mode separation (VMS) algorithm. VMS is established on optimizing a variational problem to separate different modes. It minimizes the energy overlap of the heartbeat and respiration signals as well as their harmonics with an equality constraint. Both simulation and real scene data results show that the proposed VMS algorithm is suitable for separating the weaker cardiac motion pattern from the strong respiratory motion pattern, restraining the influence of respiration harmonics on the heartbeat component. Also, the continuous remote monitoring of respiratory rate (RR) and heart rate (HR) by employing the proposed method in a real scene shows a strong consistency with the reference respiration belt and electrocardiogram (ECG). The root mean square error (RMSE) of RR and HR for the noncontact measurement are 0.13 breaths per minute (brpm) and 1.7 beats per minute (bpm), respectively.

Respiratory and thoracoabdominal motion pattern at rest and after sub-maximum effort in children with asthma

Asthma involves an increase in airway resistance even in periods between attacks, which generates changes in thoracoabdominal kinematics. The aim of the present study was to detect these adaptations at rest and after physical effort. Evaluations were performed using optoelectronic plethysmography at rest and immediately after physical effort of moderate intensity. Thirty-two children and adolescents participated in the present study (16 asthma- AG and 16 health controls-CG). After exercise, the AG exhibited a less variability of respiratory variables. The kinematic behavior of thoracoabdominal motion was the inverse of that found in healthy controls. These findings suggest mechanical and physiological adaptations to minimize the possible turbulence of the airflow and reduce the impact of airway resistance during physical exertion. Moreover, these changes are found even at rest and in patients whose asthma is clinically controlled.

Analysis of dosimetric impact of intrafraction translation and rotation during respiratory-gated stereotactic body radiotherapy with real-time tumor monitoring of the lung using a novel six degrees-of-freedom robotic moving phantom.

This study aimed to develop a six degrees-of-freedom (6DoF) robotic moving phantom for evaluating the dosimetric impact of intrafraction rotation during respiratory-gated radiotherapy with real-time tumor monitoring in the lung. Fifteen patients who had undergone respiratory-gated stereotactic body radiotherapy (SBRT) with the SyncTraX system for lung tumors were enrolled in this study. A water-equivalent phantom (WEP) was set at the tip of the robotic arm. A log file that recorded the three-dimensional positions of three fiducial markers implanted near the lung tumor was used as the input to the 6DoF robotic moving phantom. Respiratory-gated radiotherapy was performed for the WEP, which was driven using translational and rotational motions of the lung tumor. The accuracy of the 6DoF robotic moving phantom was calculated as the difference between the actual and the measured positions. To evaluate the dosimetric impact of intrafraction rotation, the absolute dose distributions under conditions involving gating and movement were compared with those under static conditions. For the sinusoidal patterns, the mean±standard deviation (SD) of the root mean square errors (RMSEs) of the translation and rotation positional errors was <0.40mm and 0.30°, respectively, for all directions. For the respiratory motion patterns of 15 patients, the mean±SD of the RMSEs of the translation and rotation positional errors was <0.55mm and 0.85°, respectively, for all directions. The γ3%/2mm values under translation with/without gating were 97.6±2.2%/80.9±18.1% and 96.8±2.3%/80.0±17.0% in the coronal and sagittal planes, respectively. Further, the γ3%/2mm values under rotation with/without gating were 91.5±6.5%/72.8±18.6% and 90.3±6.1%/72.9±15.7% in the coronal and sagittal planes, respectively. The developed 6DoF robotic phantom system could determine the translational and rotational motions of lung tumors with high accuracy. Further, respiratory-gating radiotherapy with real-time tumor monitoring using an internal surrogate marker was effective in compensating for the translational motion of lung tumors but not for correcting their rotational motion.

Simulation of dosimetry impact of 4DCT uncertainty in 4D dose calculation for lung SBRT

BackgroundDue to the heterogeneity of patient’s individual respiratory motion pattern in lung stereotactic body radiotherapy (SBRT), treatment planning dose assessment using a traditional four-dimensional computed tomography (4DCT_traditional) images based on a uniform breathing curve may not represent the true treatment dose delivered to the patient. The purpose of this study was to evaluate the accumulated dose discrepancy between based on the 4DCT_traditional and true 4DCT (4DCT_true) that incorporated with the patient’s real entire breathing motion. The study also explored a novel 4D robust planning strategy to compensate for such heterogeneity respiratory motion uncertainties.MethodsSimulated and measured patient specific breathing curves were used to generate 4D targets motion CT images. Volumetric-modulated arc therapy (VMAT) was planned using two arcs. Accumulated dose was obtained by recalculating the plan dose on each individual phase image and then deformed the dose from each phase image to the reference image. The “4 D dose” (D4D) and “true dose” (Dtrue) were the accumulated dose based on the 4DCT_traditional and 4DCT_true respectively. The average worse case dose discrepancy ( overline{Delta D} ) between D4D and Dtrue in all treatment fraction was calculated to evaluate dosimetric /planning parameters and correlate them with the heterogeneity of respiratory-induced motion patterns. A novel 4D robust optimization strategy for VMAT (4D Ro-VMAT) based on the probability density function(pdf) of breathing curve was proposed to improve the target coverage in the presence of heterogeneity respiratory motion. The data were assessed with a paired t-tests.ResultsWith increasing breathing amplitude from 5 to 20 mm, target overline{Delta {D}_{99}} , overline{Delta {D}_{95}} increased from 1.59,1.39 to 10.15%,8.66% respectively. When the standard deviation of breathing amplitude increased from 15 to 35% of the mean amplitude, overline{Delta {D}_{99}} , overline{Delta {D}_{95}} increased from 4.06,3.48 to 10.25%,6.63% respectively. The 4D Ro-VMAT plan significantly improve the target dose compared to VMAT plan.ConclusionWhen the breathing curve amplitude is more than 10 mm and standard deviation of amplitude is higher than 25% of mean amplitude, special care is needed to choose an appropriated dose accumulation approach to evaluate lung SBRT plan target coverage robustness. The proposed 4D Ro_VMAT strategy based on the pdf of patient specific breathing curve could effectively compensate such uncertainties.

Effect of gantry speed on accuracy of extracted target motion trajectories and image quality in 4D-CBCT: phantom study

Purpose. Four-dimensional cone-beam computed tomography (4D-CBCT) has attracted considerable attention due to requirements for patient motion management devices in stereotactic body radiation therapy. In addition, the determination of relevant parameters, such as gantry speed for 4D-CBCT image acquisition is important in reducing the imaging dose. The purpose of this study was to evaluate the effect of gantry speed on the tumour motion trajectory and image quality using a respiratory motion phantom. Materials and Methods. The tumour (1, 2 and 3 cm) motion trajectories were evaluated to calculate the tumour volume, centroid position, and diameter for a sinusoidal wave pattern and irregular respiratory pattern. The image quality was evaluated based on the standard deviation and contrast-to-noise ratio (CNR) of a 4D-CBCT image. Results. In terms of the tumour motion trajectories, a significant difference existed in the tumour volume and diameter between a gantry speed of 1° s–1 and high gantry speeds of 4, 5 and 6° s–1. Furthermore, the difference variation increased with an increase in the gantry speed. The centroid position of the tumour was within 1.5 mm for all gantry speeds and tumour sizes. For the irregular respiratory pattern, the difference variation in the tumour volume and diameter showed the same tendency as the sinusoidal pattern. The maximum differences of the centroid position were measured in the cases of high gantry speeds of 4, 5 and 6° s–1 for all respiratory motion patterns. With respect to image quality, the CNR was significantly lower when the gantry speed was greater than 4° s–1. Conclusion. A low gantry speed can lead to an increase in the imaging dose, whereas a high gantry speed can reduce the accuracy of the tumour motion trajectory and image quality. In our study, we estimated the appropriate gantry speed to be 3° s–1 for 4D-CBCT.

Motion robust high resolution 3D free-breathing pulmonary MRI using dynamic 3D image self-navigator.

To achieve motion robust high resolution 3D free-breathing pulmonary MRI utilizing a novel dynamic 3D image navigator derived directly from imaging data. Five-minute free-breathing scans were acquired with a 3D ultrashort echo time (UTE) sequence with 1.25 mm isotropic resolution. From this data, dynamic 3D self-navigating images were reconstructed under locally low rank (LLR) constraints and used for motion compensation with one of two methods: a soft-gating technique to penalize the respiratory motion induced data inconsistency, and a respiratory motion-resolved technique to provide images of all respiratory motion states. Respiratory motion estimation derived from the proposed dynamic 3D self-navigator of 7.5 mm isotropic reconstruction resolution and a temporal resolution of 300 ms was successful for estimating complex respiratory motion patterns. This estimation improved image quality compared to respiratory belt and DC-based navigators. Respiratory motion compensation with soft-gating and respiratory motion-resolved techniques provided good image quality from highly undersampled data in volunteers and clinical patients. An optimized 3D UTE sequence combined with the proposed reconstruction methods can provide high-resolution motion robust pulmonary MRI. Feasibility was shown in patients who had irregular breathing patterns in which our approach could depict clinically relevant pulmonary pathologies. Magn Reson Med 79:2954-2967, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Abstract ID: 15 Experimental verification of 4D Monte Carlo calculations of dose delivered to a deforming anatomy

The aim of this work is to validate 4D Monte Carlo (MC) simulation method [1] for reconstructing dose delivered to a breathing patient. Static and VMAT plans were delivered to a deformable lung phantom by an Elekta Agility linear accelerator and measured doses were compared with simulations. Measurements were performed in a deformable lung phantom containing a 2.6 cm diameter tumour with the phantom in stationary and moving (sinusoidal) states. Dose within the tumor was measured using EBT3 film and a RADPOS detector connected to the RADPOS 4D dosimetry system [2] . Dose inside the lung was measured by another RADPOS detector mounted outside the tumor at 1.5 cm from the tumor center. A single 6 MV 3 × 3 cm 2 square field and a VMAT plan, both covering the tumour, were created on the end-of-inhale CT scans using Monaco V.5.10.02. A validated BEAMnrc model of our Elekta linac was used for all MC simulations. For 4D simulations, deformation vectors were generated by deformable registration of end-of-exhale to end-of-inhale 4DCT images using Velocity AI 3.2.0 as input to the 4DdefDOSXYZnrc code along with the phantom motion trace recorded with RADPOS. Dose values from MC simulations and measurements were found to be within 3.5% of each other. The passing rate for a gamma comparison of 3%/2 mm between Monte Carlo simulations and film measurements were found to be better than 98%. In conclusion, our 4D Monte Carlo simulations using the defDOSXYZnrc code accurately calculates dose delivered to a deforming anatomy. Future work will focus on irregular respiratory motion patterns.

A novel 3D-printed phantom insert for 4D PET/CT imaging and simultaneous integrated boost radiotherapy.

To construct a 3D-printed phantom insert designed to mimic the variable PET tracer uptake seen in lung tumor volumes and a matching dosimetric insert to be used in simultaneous integrated boost (SIB) phantom studies, and to evaluate the design through end-to-end tests. A set of phantom inserts was designed and manufactured for a realistic representation of gated radiotherapy steps from 4D PET/CT scanning to dose delivery. A cylindrical phantom (φ80 × 120 mm) holds inserts for PET/CT scanning. The novel 3D printed insert dedicated to 4D PET/CT mimics high PET tracer uptake in the core and low uptake in the periphery. This insert is a variable density porous cylinder (φ44.5 × 70.0 mm), ABS-P430 thermoplastic, 3D printed by fused deposition modeling an inner (φ11 × 42 mm) cylindrical void. The square pores (1.8 × 1.8 mm2 each) fill 50% of outer volume, resulting in a 2:1 PET tracer concentration ratio in the void volume with respect to porous volume. A matching cylindrical phantom insert is dedicated to validate gated radiotherapy. It contains eight peripheral holes and one central hole, matching the location of the porous part and the void part of the 3D printed insert, respectively. These holes accommodate adaptors for Farmer-type ion chamber and cells vials. End-to-end tests were designed for imaging, planning, and dose measurements. End-to-end test were performed from 4D PET/CT scanning to transferring data to the planning system, target volume delineation, and dose measurements. 4D PET/CT scans were acquired of the phantom at different respiratory motion patterns and gating windows. A measured 2:1 18F-FDG concentration ratio between inner void and outer porous volume matched the 3D printed design. Measured dose in the dosimetric insert agreed well with planned dose on the imaging insert, within 3% for the static phantom and within 5% for most breathing patterns. The novel 3D printed phantom insert mimics variable PET tracer uptake typical of tumors. Obtained 4D PET/CT scans are suitable for segmentation and treatment planning and delivery in SIB gated treatments. Our experiments demonstrate the feasibility of this set of phantom inserts serving as end-to-end quality-assurance phantoms of SIB radiotherapy.

Impact of sampling interval in training data acquisition on intrafractional predictive accuracy of indirect dynamic tumor-tracking radiotherapy.

To explore the effect of sampling interval of training data acquisition on the intrafractional prediction error of surrogate signal-based dynamic tumor-tracking using a gimbal-mounted linac. Twenty pairs of respiratory motions were acquired from 20 patients (ten lung, five liver, and five pancreatic cancer patients) who underwent dynamic tumor-tracking with the Vero4DRT. First, respiratory motions were acquired as training data for an initial construction of the prediction model before the irradiation. Next, additional respiratory motions were acquired for an update of the prediction model due to the change of the respiratory pattern during the irradiation. The time elapsed prior to the second acquisition of the respiratory motion was 12.6 ± 3.1 min. A four-axis moving phantom reproduced patients' three dimensional (3D) target motions and one dimensional surrogate motions. To predict the future internal target motion from the external surrogate motion, prediction models were constructed by minimizing residual prediction errors for training data acquired at 80 and 320 ms sampling intervals for 20 s, and at 500, 1,000, and 2,000 ms sampling intervals for 60 s using orthogonal kV x-ray imaging systems. The accuracies of prediction models trained with various sampling intervals were estimated based on training data with each sampling interval during the training process. The intrafractional prediction errors for various prediction models were then calculated on intrafractional monitoring images taken for 30 s at the constant sampling interval of a 500 ms fairly to evaluate the prediction accuracy for the same motion pattern. In addition, the first respiratory motion was used for the training and the second respiratory motion was used for the evaluation of the intrafractional prediction errors for the changed respiratory motion to evaluate the robustness of the prediction models. The training error of the prediction model was 1.7 ± 0.7 mm in 3D for all sampling intervals. The intrafractional prediction error for the same motion pattern was 1.9 ± 0.7 mm in 3D for an 80 ms sampling interval, which increased larger than 1 mm in 10.0% of prediction models trained at a 2,000 ms sampling interval with a significant difference (P < 0.01) and up to 2.5% for the other sampling intervals without a significant difference (P > 0.05). The intrafractional prediction error for the changed respiratory motion pattern increased to 5.1 ± 2.4 mm in 3D for an 80 ms sampling interval; however, there was not a significant difference in the robustness of the prediction model between the 80 ms sampling interval and other sampling intervals (P > 0.05). Although the training error of the prediction model was consistent for the all sampling intervals, the prediction model using the larger sampling interval of the 2,000 ms increased the intrafractional prediction error for the same motion pattern. The realistic accuracy of the prediction model was difficult to estimate using the larger sampling interval during the training process. It is recommended to construct the prediction model at sampling interval ≤ 1,000 ms and to reconstruct the model during treatment.

Irregular amplitude and frequency of respiratory movements in hemispheric stroke

Objectives: The aims of the study were to investigate respiratory movement patterns among patients with right versus left hemispheric stroke with emphasis on regularity of respiratory frequency and amplitude of movements during both quiet and voluntary deep breathing and to compare the results with reference values.Materials and methods: Eighteen patients with severe stroke were measured with the Respiratory Movement Measuring Instrument. Respiratory frequencies, movements, regularity of amplitude and frequency were compared with individuals with no neurological disease.Results: The demographics and physical performance were comparable for 8 left and 10 right hemispheric stroke. Deep respiratory movements were significantly decreased (p < 0.001) and frequency significantly increased (p < 0.03 for quiet and p = 0.002 for deep breathing), for the group (n = 18) compared with reference values. Fifty-six percent of our stroke patients had irregular amplitude of deep respiratory movements (p = 0.003), and 33% had irregular frequency (p = 0.058), but none of the individuals with no neurological diseases (p = 0.003). Seventy percent of RHS patients had irregular amplitude of deep respiratory movements, compared with 38% of LHS patients (p = 0.34).Conclusion: Results show significantly decreased amplitude of deep breathing in hemispheric stroke and indicate a possible effect on regularity of range and frequency of respiratory movements.

Quantitative Study on the Effect of Abnormalities on Respiration-Induced Kidney Movement

Respiration-induced movement of abdominal organs hampers the targeting accuracy of non-invasive surgical techniques such as focused ultrasound surgery and radiosurgery. Unaccounted organ movement can result in either under dosage or damage to intervening healthy tissues. The respiration-induced movement is known to be significantly large in kidneys; however, the impact of abnormalities such as tumors and cysts on kidney movement is poorly understood. In this study, we quantified the movement patterns of kidneys in 48 normal and 62 affected kidneys (43 calcified cysts, 11 angiomyolipomas, 4 renal cell carcinomas and 4 polycystic kidneys) using ultrasound and simultaneously tracked the respiratory movement patterns using a stereo camera system. The kidneys were localized from 2-D ultrasound sequences using a template matching technique. The average movements of the right and left kidneys were, respectively, 24.54 ± 6.4 and 17.06 ± 3.66 mm in the superior-inferior and 13.62 ± 3.71 and 9.80 ± 3.32 mm in the transverse directions. Average movement in the superior-inferior direction of normal kidneys was greater than that of affected kidneys for both right (26.9 ± 5.1 vs. 22.6 ± 3.3, p < 0.001) and left (17.8 ± 2.5 vs. 16.1 ± 4.2, p = 0.01) kidneys. On the basis of spatial extent of abnormality, affected kidneys were categorized as category A (<10 mm in 26 patients), category B (10–20 mm in 22 patients) and category C (>20 mm in 14 patients). Compared with normal patients, the extent of movement was significantly reduced in abnormal categories B (p < 0.001) and C (p < 0.001), but the change was not significant in category A (p = 0.04). Hysteresis plots of the kidneys revealed a maximum change of 12.3 mm. The movement patterns of the kidneys also closely correlated with the respiratory movement pattern (Pearson correlation = 0.89 [right] and 0.87 [left]). We expect that the movement pattern analyses and quantification carried out in this study would aid in developing movement adaptive surgical protocols for non-invasive treatment of kidney tumors/cancers.

Respiratory surface motion measurement by Microsoft Kinect

Abstract In radiotherapy of abdominal and thoracic tumors, respiratory motion is a problem for an accurate treatment. Most current motion compensation techniques rely on externally acquired breathing signals of the patient. The systems in clinical use usually work with 1D surface motion signals to describe internal structure respiratory motion patterns. As a 1D signal is not able to describe complex motion patterns and breathing variations, in this work the Microsoft Kinect, which can record multidimensional respiratory surface motion signals, is proposed to be used instead. For the Kinect, a clinically acceptable measurement setup is designed and Kinect measurements are compared to the Varian RPM system (clinical standard). The results show that the signals are well aligned. An additional comparison of Kinect signals from different regions of interest on the chest further reveals variations between them. This illustrates that the use of a system that provides multidimensional signals is worthwhile; the knowledge about breathing variations could be applied for optimization of current clinical workflows.

Realistic respiratory motion margins for external beam partial breast irradiation.

Respiratory margins for partial breast irradiation (PBI) have been largely based on geometric observations, which may overestimate the margin required for dosimetric coverage. In this study, dosimetric population-based respiratory margins and margin formulas for external beam partial breast irradiation are determined. Volunteer respiratory data and anterior-posterior (AP) dose profiles from clinical treatment plans of 28 3D conformal radiotherapy (3DCRT) PBI patient plans were used to determine population-based respiratory margins. The peak-to-peak amplitudes (A) of realistic respiratory motion data from healthy volunteers were scaled from A = 1 to 10 mm to create respiratory motion probability density functions. Dose profiles were convolved with the respiratory probability density functions to produce blurred dose profiles accounting for respiratory motion. The required margins were found by measuring the distance between the simulated treatment and original dose profiles at the 95% isodose level. The symmetric dosimetric respiratory margins to cover 90%, 95%, and 100% of the simulated treatment population were 1.5, 2, and 4 mm, respectively. With patient set up at end exhale, the required margins were larger in the anterior direction than the posterior. For respiratory amplitudes less than 5 mm, the population-based margins can be expressed as a fraction of the extent of respiratory motion. The derived formulas in the anterior/posterior directions for 90%, 95%, and 100% simulated population coverage were 0.45A/0.25A, 0.50A/0.30A, and 0.70A/0.40A. The differences in formulas for different population coverage criteria demonstrate that respiratory trace shape and baseline drift characteristics affect individual respiratory margins even for the same average peak-to-peak amplitude. A methodology for determining population-based respiratory margins using real respiratory motion patterns and dose profiles in the AP direction was described. It was found that the currently used respiratory margin of 5 mm in partial breast irradiation may be overly conservative for many 3DCRT PBI patients. Amplitude alone was found to be insufficient to determine patient-specific margins: individual respiratory trace shape and baseline drift both contributed to the dosimetric target coverage. With respiratory coaching, individualized respiratory margins smaller than the full extent of motion could reduce planning target volumes while ensuring adequate coverage under respiratory motion.

T2-weighted four dimensional magnetic resonance imaging with result-driven phase sorting.

T2-weighted MRI provides excellent tumor-to-tissue contrast for target volume delineation in radiation therapy treatment planning. This study aims at developing a novel T2-weighted retrospective four dimensional magnetic resonance imaging (4D-MRI) phase sorting technique for imaging organ/tumor respiratory motion. A 2D fast T2-weighted half-Fourier acquisition single-shot turbo spin-echo MR sequence was used for image acquisition of 4D-MRI, with a frame rate of 2-3 frames/s. Respiratory motion was measured using an external breathing monitoring device. A phase sorting method was developed to sort the images by their corresponding respiratory phases. Besides, a result-driven strategy was applied to effectively utilize redundant images in the case when multiple images were allocated to a bin. This strategy, selecting the image with minimal amplitude error, will generate the most representative 4D-MRI. Since we are using a different image acquisition mode for 4D imaging (the sequential image acquisition scheme) with the conventionally used cine or helical image acquisition scheme, the 4D dataset sufficient condition was not obviously and directly predictable. An important challenge of the proposed technique was to determine the number of repeated scans (NR) required to obtain sufficient phase information at each slice position. To tackle this challenge, the authors first conducted computer simulations using real-time position management respiratory signals of the 29 cancer patients under an IRB-approved retrospective study to derive the relationships between NR and the following factors: number of slices (NS), number of 4D-MRI respiratory bins (NB), and starting phase at image acquisition (P0). To validate the authors' technique, 4D-MRI acquisition and reconstruction were simulated on a 4D digital extended cardiac-torso (XCAT) human phantom using simulation derived parameters. Twelve healthy volunteers were involved in an IRB-approved study to investigate the feasibility of this technique. 4D data acquisition completeness (Cp) increases as NR increases in an inverse-exponential fashion (Cp = 100 - 99 × exp(-0.18 × NR), when NB = 6, fitted using 29 patients' data). The NR required for 4D-MRI reconstruction (defined as achieving 95% completeness, Cp = 95%, NR = NR,95) is proportional to NB (NR,95 ∼ 2.86 × NB, r = 1.0), but independent of NS and P0. Simulated XCAT 4D-MRI showed a clear pattern of respiratory motion. Tumor motion trajectories measured on 4D-MRI were comparable to the average input signal, with a mean relative amplitude error of 2.7% ± 2.9%. Reconstructed 4D-MRI for healthy volunteers illustrated clear respiratory motion on three orthogonal planes, with minimal image artifacts. The artifacts were presumably caused by breathing irregularity and incompleteness of data acquisition (95% acquired only). The mean relative amplitude error between critical structure trajectory and average breathing curve for 12 healthy volunteers is 2.5 ± 0.3 mm in superior-inferior direction. A novel T2-weighted retrospective phase sorting 4D-MRI technique has been developed and successfully applied on digital phantom and healthy volunteers.

SU‐E‐J‐123: Assessing Segmentation Accuracy of Internal Volumes and Sub‐Volumes in 4D PET/CT of Lung Tumors Using a Novel 3D Printed Phantom

Purpose:To assess the accuracy of internal target volume (ITV) segmentation of lung tumors for treatment planning of simultaneous integrated boost (SIB) radiotherapy as seen in 4D PET/CT images, using a novel 3D‐printed phantom.Methods:The insert mimics high PET tracer uptake in the core and 50% uptake in the periphery, by using a porous design at the periphery. A lung phantom with the insert was placed on a programmable moving platform. Seven breathing waveforms of ideal and patient‐specific respiratory motion patterns were fed to the platform, and 4D PET/CT scans were acquired of each of them. CT images were binned into 10 phases, and PET images were binned into 5 phases following the clinical protocol. Two scenarios were investigated for segmentation: a gate 30–70 window, and no gating. The radiation oncologist contoured the outer ITV of the porous insert with on CT images, while the internal void volume with 100% uptake was contoured on PET images for being indistinguishable from the outer volume in CT images. Segmented ITVs were compared to the expected volumes based on known target size and motion.Results:3 ideal breathing patterns, 2 regular‐breathing patient waveforms, and 2 irregular‐breathing patient waveforms were used for this study. 18F‐FDG was used as the PET tracer. The segmented ITVs from CT closely matched the expected motion for both no gating and gate 30–70 window, with disagreement of contoured ITV with respect to the expected volume not exceeding 13%. PET contours were seen to overestimate volumes in all the cases, up to more than 40%.Conclusion:4DPET images of a novel 3D printed phantom designed to mimic different uptake values were obtained. 4DPET contours overestimated ITV volumes in all cases, while 4DCT contours matched expected ITV volume values. Investigation of the cause and effects of the discrepancies is undergoing.

WE-AB-204-03: A Novel 3D Printed Phantom for 4D PET/CT Imaging and SIB Radiotherapy Verification

Purpose: To construct and test a 3D printed phantom designed to mimic variable PET tracer uptake seen in lung tumor volumes. To assess segmentation accuracy of sub-volumes of the phantom following 4D PET/CT scanning with ideal and patient-specific respiratory motion. To plan, deliver and verify delivery of PET-driven, gated, simultaneous integrated boost (SIB) radiotherapy plans. Methods: A set of phantoms and inserts were designed and manufactured for a realistic representation of lung cancer gated radiotherapy steps from 4D PET/CT scanning to dose delivery. A cylindrical phantom (40x 120 mm) holds inserts for PET/CT scanning. The novel 3D printed insert dedicated to 4D PET/CT mimics high PET tracer uptake in the core and lower uptake in the periphery. This insert is a variable density porous cylinder (22.12×70 mm), ABS-P430 thermoplastic, 3D printed by uPrint SE Plus with inner void volume (5.5×42 mm). The square pores (1.8×1.8 mm2 each) fill 50% of outer volume, resulting in a 2:1 SUV ratio of PET-tracer in the void volume with respect to porous volume. A matching in size cylindrical phantom is dedicated to validate gated radiotherapy. It contains eight peripheral holes matching the location of the porous part of the 3D printed insert, and one central hole. These holes accommodate adaptors for Farmer-type ion chamber and cells vials. Results: End-to-end test were performed from 4D PET/CT scanning to transferring data to the planning system and target volume delineation. 4D PET/CT scans were acquired of the phantom with different respiratory motion patterns and gating windows. A measured 2:1 18F-FDG SUV ratio between inner void and outer volume matched the 3D printed design. Conclusion: The novel 3D printed phantom mimics variable PET tracer uptake typical of tumors. Obtained 4D PET/CT scans are suitable for segmentation, treatment planning and delivery in SIB gated treatments of NSCLC.

TH-CD-207-09: Retrospective 4D-MRI with a Novel Image-Based Surrogate: A Sagittal-Coronal-Diaphragm Point of Intersection (SCD-PoI) Motion Tracking Method

Purpose: The unreliable stability of internal respiratory surrogates and inconvenience of external respiratory surrogates for current retrospective 4D-MRI techniques largely affects the image quality of 4D-MRI. This study aims at developing image-based surrogate, a sagittal-coronal-diaphragm point of intersection (SCD-PoI) motion tracking method for retrospective 4D-MRI reconstruction.Methods/materials: As a pre-estimate of respiratory motion pattern, single-slice sagittal cines (FIESTA) were acquired at a location near the dome of the diaphragm. Subsequently, multi-slice coronal cines (FIESTA) were acquired and used for 4D-MRI reconstruction with phase sorting. Diaphragm motion trajectories were measured from the point of intersection between sagittal MRI cine plane, coronal MRI cine plain and the diaphragm dome surface. This point is defined as sagittal-coronal-diaphragm point of intersection (SCD-PoI). We pre-estimate respiraotyr motion by tracking SCD-PoI on sagitall cine. Then coronal images were then re-binned to different phased bins according to SCD-PoI motion tracking on coronal cine. This 4D-MRI technique was evaluated on a 4D Digital Extended Cardiac-Torso (XCAT) human phantom with a hypothesized moving tumor, six healthy voluneteers and two cancer patients under an IRB-approved study. Region of interest (ROI: tumor for XCAT and patients, dome of left kidney for healthy volunteers) trajectories on 4D-MRI were measured and compared with the reference (input respiratory curve for XCAT and ROI trajectories extracted from reference single-slice MRI cine (FIESTA) for human subjects). Superior-inferior (SI) mean absolute amplitude difference (D) and cross-correlation coefficient (CC) were calculated. Results: 4D-MRI on XCAT demonstrated highly accurate motion information with a low D (1.13mm) and a high CC (0.98) in the SI direction. Minimal artifacts were observed in human participants’ 4D-MRI, and images were adequate to reveal the respiratory motion of organs and tumor (D=1.08±1.03mm; CC=0.96). Conclusion: A novel 4D-MRI technique with image-based respiratory surrogate has been developed and tested on a digital phantom and human subjects.

Accuracy of amplitude-based respiratory gating for PET/CT in irregular respirations.

We evaluated the accuracy of amplitude gating PET (AG-PET) compared with phase gating PET (PG-PET) in relation to respiratory motion patterns based on a phantom analysis. We used a NEMA IEC body phantom filled with an (18)F solution with a 4:1 sphere-to-background radioactivity ratio (12.6 and 2.97 kBq/mL). PET/CT scans were acquired in a motionless and moving state on a Biograph mCT. The respiratory movements were simulated by four different waveform patterns consisting of ideal breathing, breathing with a pause period, breathing with a variable amplitude and breathing with a changing baseline. AG-PET selects the narrow bandwidth containing 20 % of the respiratory cycle. PG-PET was reconstructed with five gates. The image quality was physically assessed using the percent contrast (Q H,10mm), background variability (N 10mm) recovery coefficient (RC), and sphere volumes. In regular motion patterns with ideal breathing and breathing with a pause period, the Q H,10mm, RC and sphere volumes were not different between AG-PET and PG-PET. In the variable amplitude pattern, the Q H,10mm of AG-PET was higher than that of PG-PET (35.8 vs 28.2 %), the RC of AG-PET was higher than that of PG-PET and sphere volume of AG-PET was smaller than that of PG-PET (6.4 vs 8.6 mL). In the changing baseline pattern, the Q H,10mm of AG-PET was higher than that of PG-PET (42.4 vs 16.7 %), the RC of AG-PET was higher than that of PG-PET and sphere volume of AG-PET was smaller than that of PG-PET (6.2 vs 9.8 mL). The N 10mm did not differ between AG-PET and PG-PET, irrespective of the motion pattern. Amplitude gating PET is considered to be more accurate than phase gating PET for examining unstable respiratory motion patterns, such as those involving a variable amplitude or changing baseline.

MO‐A‐BRD‐08: Radiosurgery Beyond Cancer: Real‐Time Target Localization and Treatment Planning for Cardiac Radiosurgery Under MRI Guidance

Purpose:Atrial fibrillation (AF) is the most common cardiac arrhythmia, affecting &gt;2.5M Americans and &gt;4.5M Europeans. AF is usually treated with minimally‐invasive, time consuming catheter ablation techniques. Radiosurgery of the pulmonary veins (PV) has been proposed for AF treatment, however is challenging due to the complex respiratory and cardiac motion patterns. We hypothesize that an MRI‐linac could solve the difficult real‐time targeting and adaptation problem. In this study we quantified target motion ranges on cardiac MRI and analyzed the dosimetric benefits of margin reduction assuming real‐time MRI tracking was applied.Methods:For the motion study, four human subjects underwent real‐time cardiac MRI under free breathing. The target motion on coronal and axial cine planes was analyzed using a template matching algorithm. For the planning study, an ablation line at each PV antrum was defined as target on an AF patient scheduled for catheter ablation. Various safety margins ranging from 0mm (perfect tracking) to 8mm (untracked motion) were added to the target defining the PTV. 30Gy single fraction IMRT plans were then generated. Finally, the influence of a 1T magnetic field on treatment beam delivery was calculated using the Geant4 Monte Carlo algorithm to simulate the dosimetric impact of MRI guidance.Results:The motion study showed the mean respiratory motion of the target area on MRI was 8.4mm (SI), 1.7mm (AP) and 0.3mm (LR). Cardiac motion was small (&lt;2mm). The planning study showed that with increasing safety margins to encompass untracked motion, dose tolerances for OARs such as the esophagus and airways were exceeded by &gt;100%. The magnetic field had little impact on the dose distribution.Conclusion:Our results indicate that real‐time MRI tracking of the PVs seems feasible. Accurate image guidance for high‐dose AF radiosurgery is essential since safety margins covering untracked target motion will result in unacceptable treatment plans.

MO‐G‐18C‐05: Real‐Time Prediction in Free‐Breathing Perfusion MRI

Purpose:The aim is to minimize frame‐wise difference errors caused by respiratory motion and eliminate the need for breath‐holds in magnetic resonance imaging (MRI) sequences with long acquisitions and repeat times (TRs). The technique is being applied to perfusion MRI using arterial spin labeling (ASL).Methods:Respiratory motion prediction (RMP) using navigator echoes was implemented in ASL. A least‐square method was used to extract the respiratory motion information from the 1D navigator. A generalized artificial neutral network (ANN) with three layers was developed to simultaneously predict 10 time points forward in time and correct for respiratory motion during MRI acquisition. During the training phase, the parameters of the ANN were optimized to minimize the aggregated prediction error based on acquired navigator data. During realtime prediction, the trained ANN was applied to the most recent estimated displacement trajectory to determine in real‐time the amount of spatialResults:The respiratory motion information extracted from the least‐square method can accurately represent the navigator profiles, with a normalized chi‐square value of 0.037±0.015 across the training phase. During the 60‐second training phase, the ANN successfully learned the respiratory motion pattern from the navigator training data. During real‐time prediction, the ANN received displacement estimates and predicted the motion in the continuum of a 1.0 s prediction window. The ANN prediction was able to provide corrections for different respiratory states (i.e., inhalation/exhalation) during real‐time scanning with a mean absolute error of &lt; 1.8 mm.Conclusion:A new technique enabling free‐breathing acquisition during MRI is being developed. A generalized ANN development has demonstrated its efficacy in predicting a continuum of motion profile for volumetric imaging based on navigator inputs. Future work will enhance the robustness of ANN and verify its effectiveness with human subjects.Research supported by National Institutes of Health National Cancer Institute Grant R01 CA159471‐01