In-room Magnetic Resonance Imaging (MRI) allows the acquisition of fast 2D cine-18 MRI centered i... more In-room Magnetic Resonance Imaging (MRI) allows the acquisition of fast 2D cine-18 MRI centered in the tumor for advanced motion management in radiotherapy. To 19 achieve 3D information during treatment, patient-specific motion models can be 20 considered the most viable solution. However, conventional global motion models are 21 built using a single motion surrogate, independently from the anatomical location. 22 In this work, we present a novel motion model based on regions of interest (ROIs) 23 established on 4D Computed Tomography (4DCT) and 2D cine-MRI, aiming at 24 accurately compensating for changes during treatment. In the planning phase, a 25 motion model is built on a 4DCT dataset, through 3D deformable image registration 26 (DIR). ROIs are then defined and correlated with motion fields derived by 2D DIR 27 between CT slices centered in the tumor. In the treatment phase, the model is applied 28 to in-room cine-MRI data to compensate for organ motion in a multi-modal framework, 29 aiming at estimating a time-resolved 3DCT. 30 The method is validated on a digital phantom and tested on two lung patients. Analysis 31 is performed by considering different anatomical planes (coronal, sagittal and a 32 combination of the two) and evaluating the performance of the method on tumor and 33 diaphragm. For the phantom study, the ROI-based model results in a uniform median 34 error on both diaphragm and tumor below 1.5mm. For what concerns patients, median 35 errors on both diaphragm and tumor are around 2mm (maximum patient resolution), 36 confirming the capability of the method to regionally compensate for motion. 37 A novel ROI-based motion model is proposed as an integral part of an envisioned 38 clinical MRI-guided workflow aiming at enhanced image guidance compared to 39 conventional strategies. 40 41 *
ESTRO 35 2016 S73 _______________________________________________________________________________... more ESTRO 35 2016 S73 ______________________________________________________________________________________________________ centroid coordinates and the detected location was larger than 2.7mm in plane and 3mm in slice direction. Results: Table1 shows the average AUC values for the model results of all patients using a single sequence and when combined. The combined model (AUC=0.94) performs significantly better than the best imaging sequence alone (T1-THRIVE AUC=0.84). Without post-processing the model correctly identifies 80/86 markers but with a total of 98 FP. After post-processing, we reduced the FP to a total of 20 but the true positives (TP) were also reduced to 66. Figure 1 shows the model pipeline. Deviations between the reference and the correctly identified marker location are < 1mm.
In lung radiotherapy, variations in cycle-to-cycle breathing results in four-dimensional computed... more In lung radiotherapy, variations in cycle-to-cycle breathing results in four-dimensional computed tomography imaging artifacts, leading to inaccurate beam coverage and tumor targeting. In previous studies, the effect of audiovisual (AV) biofeedback on the external respiratory signal reproducibility has been investigated but the internal anatomy motion has not been fully studied. The aim of this study is to test the hypothesis that AV biofeedback improves diaphragm motion reproducibility of internal anatomy using magnetic resonance imaging (MRI). Methods: To test the hypothesis 15 healthy human subjects were enrolled in an ethics-approved AV biofeedback study consisting of two imaging sessions spaced ∼1 week apart. Within each session MR images were acquired under free breathing and AV biofeedback conditions. The respiratory signal to the AV biofeedback system utilized optical monitoring of an external marker placed on the abdomen. Synchronously, serial thoracic 2D MR images were obtained to measure the diaphragm motion using a fast gradient-recalled-echo MR pulse sequence in both coronal and sagittal planes. The improvement in the diaphragm motion reproducibility using the AV biofeedback system was quantified by comparing cycle-to-cycle variability in displacement, respiratory period, and baseline drift. Additionally, the variation in improvement between the two sessions was also quantified. Results: The average root mean square error (RMSE) of diaphragm cycle-to-cycle displacement was reduced from 2.6 mm with free breathing to 1.6 mm (38% reduction) with the implementation of AV biofeedback (p-value < 0.0001). The average RMSE of the respiratory period was reduced from 1.7 s with free breathing to 0.3 s (82% reduction) with AV biofeedback (p-value < 0.0001). Additionally, the average baseline drift obtained using a linear fit was reduced from 1.6 mm/min with free breathing to 0.9 mm/min (44% reduction) with AV biofeedback (p-value = 0.012). The diaphragm motion reproducibility improvements with AV biofeedback were consistent with the abdominal motion reproducibility that was observed from the external marker motion variation. Conclusions: This study was the first to investigate the potential of AV biofeedback to improve the motion reproducibility of internal anatomy using MRI. The study demonstrated the significant improvement in diaphragm motion reproducibility using AV biofeedback combined with MRI. This system can potentially provide clinically beneficial motion management of internal anatomy in MRI and radiotherapy.
The use of trajectory log files for routine patient quality assurance is gaining acceptance. Such... more The use of trajectory log files for routine patient quality assurance is gaining acceptance. Such use requires the validation of the trajectory log itself. However, the accurate localization of a multileaf collimator (MLC) leaf while it is in motion remains a challenging task. We propose an efficient phantom-less technique using the EPID to verify the dynamic MLC positions with high accuracy. Measurements were made on four Varian TrueBeams equipped with M120 MLCs. Two machines were equipped with the S1000 EPID; two were equipped with the S1200 EPID. All EPIDs were geometrically corrected prior to measurements. Dosimetry mode EPID measurements were captured by a frame grabber card directly linked to the linac. All leaf position measurements were corrected both temporally and geometrically. The readout latency of each panel, as a function of pixel row, was determined using a 40 × 1.0 cm 2 sliding window (SW) field moving at 2.5 cm/s orthogonal to the row readout direction. The latency of each panel type was determined by averaging the results of two panels of the same type. Geometric correction was achieved by computing leaf positions with respect to the projected isocenter position as a function of gantry angle. This was determined by averaging the central axis position of fields at two collimator positions of 90°and 270°. The radiological to physical leaf end position was determined by comparison of the measured gap with that determined using a feeler gauge. The radiological to physical leaf position difference was found to be 0.1 mm. With geometric and latency correction, the proposed method was found to be improve the ability to detect dynamic MLC positions from 1.0 to 0.2 mm for all leaves. Latency and panel residual geometric error correction improve EPID-based MLC position measurement. These improvements provide for the first time a trajectory log QA procedure.
Pearson's linear correlation coefficient). MHW Heart was retained as MHD surrogate. MHW Heart = 1... more Pearson's linear correlation coefficient). MHW Heart was retained as MHD surrogate. MHW Heart = 1.5 cm was found to be the most optimal threshold to identify patients with MHD > 3.5 Gy (Y = 1.705). These results lead to the development of the DIBH decision-making procedure: 1) single CT-slice acquisition (Figure (b)), 2) projection of the mean medial field setup, 3) MHW measurement and 4) DIBH decision-making. This procedure was found to have a sensitivity of 87.5% and a specificity of 90.9%. Patients stratified to FB-WBRT (10/30) had a clinically acceptable average MHD: 2.8 ± 1.4 Gy (range: 1.0-5.3 Gy). Patients stratified to DIBH-WBRT (20/30) had significantly higher average MHD during FB-WBRT: 6.5 ± 2.6 Gy (range: 2.9-11.1 Gy) (p < 0.001, t-test), indeed needing MHD reduction. Conclusions: DIBH decision-making based on single CT-slice acquisition is feasible in left-sided WBRT. It is followed by the acquisition of 1 CT-scan, during FB or DIBH. The proposed procedure therefore halves the workload of DIBH decisionmaking during treatment planning.
The use of super-paramagnetic iron oxide nanoparticles (SPIONs) as an MRI contrast agent (SPION-C... more The use of super-paramagnetic iron oxide nanoparticles (SPIONs) as an MRI contrast agent (SPION-CA) can safely label hepatic macrophages and be localized within hepatic parenchyma for T2*- and R2*-MRI of the liver. To date, no study has utilized the R2*-MRI with SPIONs for quantifying liver heterogeneity to characterize functional liver parenchyma (FLP) and hepatic tumors. This study investigates whether SPIONs enhance liver heterogeneity for an auto-contouring tool to identify the voxel-wise functional liver parenchyma volume (FLPV). This was the first study to directly evaluate the impact of SPIONs on the FLPV in R2*-MRI for 12 liver cancer patients. By using SPIONs, liver heterogeneity was improved across pre- and post-SPION MRI sessions. On average, 60% of the liver [range 40–78%] was identified as the FLPV in our auto-contouring tool with a pre-determined threshold of the mean R2* of the tumor and liver. This method performed well in 10 out of 12 liver cancer patients; the rema...
Journal of medical imaging and radiation oncology, 2018
In-room MRI is a promising image guidance strategy in external beam radiotherapy to acquire volum... more In-room MRI is a promising image guidance strategy in external beam radiotherapy to acquire volumetric information for moving targets. However, limitations in spatio-temporal resolution led several authors to use 2D orthogonal images for guidance. The aim of this work is to present a method to concurrently compensate for non-rigid tumour motion and provide an approach for 3D reconstruction from 2D orthogonal cine-MRI slices for MRI-guided treatments. Free-breathing sagittal/coronal interleaved 2D cine-MRI were acquired in addition to a pre-treatment 3D volume in two patients. We performed deformable image registration (DIR) between cine-MRI slices and corresponding slices in the pre-treatment 3D volume. Based on an extrapolation of the interleaved 2D motion fields, the 3D motion field was estimated and used to warp the pre-treatment volume. Due to the lack of a ground truth for patients, the method was validated on a digital 4D lung phantom. On the phantom, the 3D reconstruction met...
Several image-based retrospective sorting methods of 4D magnetic resonance imaging (4D MRI) have ... more Several image-based retrospective sorting methods of 4D magnetic resonance imaging (4D MRI) have been proposed for respiratory motion reconstruction in external beam radiotherapy. However, the optimal strategy for providing accurate and artifact-free 4D MRI, ideally corresponding to an average breathing cycle, is not yet defined. This study presents a proactive comparison of three published image-based sorting methods, to define a groundwork for benchmarking in 4D MRI. Three published 4D MRI methods were selected for image retrospective sorting: body area, mutual information, and navigator slice. The three image-based methods were compared against a conventional retrospective sorting method based on an external surrogate. Comparisons were performed by means of an MRI digital phantom, derived from the XCAT CT phantom generated with different patient-derived signals, for a total of 12 cases. Specific multislice MRI acquisitions were simulated for slice sorting and sagittal, coronal, a...
Breathing management can reduce breath-to-breath (intrafraction) and day-by-day (interfraction) v... more Breathing management can reduce breath-to-breath (intrafraction) and day-by-day (interfraction) variability in breathing motion while utilizing the respiratory motion of internal and external surrogates for respiratory guidance. Audiovisual (AV) biofeedback, an interactive personalized breathing motion management system, has been developed to improve reproducibility of intra- and interfraction breathing motion. However, the assumption of the correlation of respiratory motion between surrogates and tumors is not always verified during medical imaging and radiation treatment. Therefore, the aim of the study was to test the hypothesis that the correlation of respiratory motion between surrogates and tumors is the same under free breathing without guidance (FB) and with AV biofeedback guidance for voluntary motion management. For 13 lung cancer patients receiving radiotherapy, 2D coronal and sagittal cine-MR images were acquired across two MRI sessions (pre- and mid-treatment) with two ...
Australasian Physical & Engineering Sciences in Medicine, 2014
This study evaluated if an audiovisual (AV) biofeedback causes variation in the level of external... more This study evaluated if an audiovisual (AV) biofeedback causes variation in the level of external and internal correlation due to its interactive intervention in natural breathing. The internal (diaphragm) and external (abdominal wall) respiratory motion signals of 15 healthy human subjects under AV biofeedback and free breathing (FB) were analyzed and measures of correlation and regularity taken. Regularity metrics (root mean square error and spectral power dispersion metric) were obtained and the correlation between these metrics and the internal and external correlation was investigated. For FB and AV biofeedback assisted breathing the mean correlations found between internal and external respiratory motion were 0.96 ± 0.02 and 0.96 ± 0.03, respectively. This means there is no evidence to suggest (p-value = 0.88) any difference in the correlation between internal and external respiratory motion with the use of AV biofeedback. Our results confirmed the hypothesis that the internal-external correlation with AV biofeedback is the same as for free breathing. Should this correlation be maintained for patients, AV biofeedback can be implemented in the clinic with confidence as regularity improvements using AV biofeedback with an external signal will be reflected in increased internal motion regularity.
Innovation/Impact: We propose a dynamic keyhole method for MR image reconstruction using respirat... more Innovation/Impact: We propose a dynamic keyhole method for MR image reconstruction using respiratory external/internal surrogate motion for real-time tumor monitoring in image guided radiotherapy (IGRT). Using dynamic keyhole method with 47 datasets eliminates the known artifacts while retaining high image quality for shorter acquisition times.
International Journal of Radiation Oncology*Biology*Physics, 2016
To assess the impact of an audiovisual (AV) biofeedback on intra-and interfraction tumor motion f... more To assess the impact of an audiovisual (AV) biofeedback on intra-and interfraction tumor motion for lung cancer patients. Methods and Materials Lung tumor motion was investigated in 9 lung cancer patients who underwent a breathing training session with AV biofeedback before 2 3T magnetic resonance imaging (MRI) sessions. The breathing training session was performed to allow patients to become familiar with AV biofeedback, which uses a guiding wave customized for each patient according to a reference breathing pattern. In the first MRI session (pretreatment), 2-dimensional cine-MR images with (1) free breathing (FB) and (2) AV biofeedback were obtained, and the second MRI session was repeated within 3-6 weeks (mid-treatment). Lung tumors were directly measured from cine-MR images using an auto-segmentation technique; the centroid and outlier motions of the lung tumors were measured from the segmented tumors. Free breathing and AV biofeedback were compared using several metrics: intra-and interfraction tumor motion consistency in displacement and period, and the outlier motion ratio. Results Compared with FB, AV biofeedback improved intrafraction tumor motion consistency by 34% in displacement (P=.019) and by 73% in period (P<.001). Compared with FB, AV biofeedback improved interfraction tumor motion consistency by 42% in displacement (P<.046) and by 74% in period (P=.005). Compared with FB, AV biofeedback reduced the outlier motion ratio by 21% (P<.001). Conclusions These results demonstrated that AV biofeedback significantly improved intra-and interfraction lung tumor motion consistency for lung cancer patients. These results demonstrate that AV biofeedback can facilitate consistent tumor motion, which is advantageous toward achieving more accurate medical imaging and radiation therapy procedures. * Paired Student t test between FB and AV biofeedback (coronal and sagittal together).
Journal of Medical Imaging and Radiation Oncology, 2019
Introduction 4D-MRI, compared to 4D-CT, provides better soft-tissue contrast for target delineati... more Introduction 4D-MRI, compared to 4D-CT, provides better soft-tissue contrast for target delineation. However, motion artefacts are often observed due to residual breathing variations. This study is to present a retrospective 4D-MRI reconstruction method based on 2D diaphragm profiles to improve the quality of 4D-MR images in the presence of significant breathing variations. Methods The proposed 4D-MRI reconstruction method utilized diaphragm profiles (2D cine images on a single sagittal plan at the peak diaphragm) in conjunction with 4D-MR scans (2D-cine images on multiple predetermined coronal planes along the anterior-posterior direction over a volume of interest). The diaphragm profile images were exploited to sort the 4D-MR scans by matching respiratory amplitude of diaphragm on the 4D-MR scans to the diaphragm profiles. To evaluate reconstructed 4D-MR images (ten 3D-MR images), sagittal images on ten 3D-MR images under free breathing (FB) and respiratory guidance (GB) were compared with diaphragm profile images (reference) from 13 healthy volunteers. Results Forty-four 4D-MR scan datasets were successfully reconstructed without distinct respiratory-related motion artefacts even with the presence of breathing variation. The differences in diaphragm profiles between the reference and corresponding reconstructed images in the mean of root mean square were similar between FB (3.5 mm) and GB (3.0 mm), confirming that the 4D-MRI reconstruction method was effective even with significant breathing variation. Conclusions The diaphragm profiles were utilized to reconstruct 4D-MR images with spatial reliability and a fixed scan time under FB and GB. Our method can provide reliable 4D information of thoracic and abdominal regions for MRI-guided radiotherapy.
Respiratory variation can increase the variability of tumor position and volume, accounting for l... more Respiratory variation can increase the variability of tumor position and volume, accounting for larger treatment margins and longer treatment times. Audiovisual biofeedback as a breath-hold technique could be used to improve the reproducibility of lung tumor positions at inhalation and exhalation for the radiation therapy of mobile lung tumors. This study aimed to assess the impact of audiovisual biofeedback breath-hold (AVBH) on interfraction lung tumor position reproducibility and volume consistency for respiratory-gated lung cancer radiation therapy. Methods: Lung tumor position and volume were investigated in 9 patients with lung cancer who underwent a breath-hold training session with AVBH before 2 magnetic resonance imaging (MRI) sessions. During the first MRI session (before treatment), inhalation and exhalation breath-hold 3dimensional MRI scans with conventional breath-hold (CBH) using audio instructions alone and AVBH were acquired. The second MRI session (midtreatment) was repeated within 6 weeks after the first session. Gross tumor volumes (GTVs) were contoured on each dataset. CBH and AVBH were compared in terms of tumor position reproducibility as assessed by GTV centroid position Sources of support: This study was supported by an NHMRC Australia Fellowship.
The dynamic keyhole is a new MR image reconstruction method for thoracic and abdominal MR imaging... more The dynamic keyhole is a new MR image reconstruction method for thoracic and abdominal MR imaging. To date, this method has not been investigated with cancer patient MRI data. The goal of this study was to assess the dynamic keyhole method for the task of lung tumor localization using cine-MR images reconstructed in the presence of respiratory motion. Methods: The dynamic keyhole method utilizes a previously acquired a library of peripheral k-space datasets at similar displacement and phase (where phase is simply used to determine whether the breathing is inhale to exhale or exhale to inhale) respiratory bins in conjunction with central k-space datasets (keyhole) acquired. External respiratory signals drive the process of sorting, matching and combining the two k-space streams for each respiratory bin, thereby achieving faster image acquisition without substantial motion artifacts. This study was the first that investigates the impact of k-space undersampling on lung tumor motion and area assessment across clinically available techniques (zero-filling and conventional keyhole). In this study, the dynamic 2 keyhole, conventional keyhole and zero-filling methods were compared to full k-space dataset acquisition by quantifying (1) keyhole size required for central k-space datasets for constant image quality across sixty four cine-MRI datasets from nine lung cancer patients, (2) the intensity difference between the original and reconstructed images in a constant keyhole size, and (3) the accuracy of tumor motion and area directly measured by tumor auto-contouring. Results: For constant image quality, the dynamic keyhole method, conventional keyhole and zero-filling methods required 22%, 34% and 49% of the keyhole size (P < 0.0001), respectively, compared to the full kspace image acquisition method. Compared to the conventional keyhole and zero-filling reconstructed images with the keyhole size utilized in the dynamic keyhole method, an average intensity difference of the dynamic keyhole reconstructed images (P < 0.0001) was minimal, and resulted in the accuracy of tumor motion within 99.6% (P < 0.0001) and the accuracy of tumor area within 98.0% (P < 0.0001) for lung tumor monitoring applications. Conclusions: This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image-guided radiation therapy requiring the MR monitoring of thoracic tumors. Based on the results from this study, the dynamic keyhole method could increase the imaging frequency by up to a factor of five compared with full k-space methods for real-time lung tumor MRI.
The aim of the project is to test the hypothesis that quasi-breath-hold (QBH) biofeedback improve... more The aim of the project is to test the hypothesis that quasi-breath-hold (QBH) biofeedback improves the residual respiratory motion management within a gating window, reducing respiratory motion artifacts in gated 3D thoracic MR images. A QBH biofeedback system has been employed with gated 3D thoracic MRI acquisitions. The QBH biofeedback system utilized (1) the external marker position on the abdomen using an RPM system (Real-time Position Management, Varian) to audio-visually guide a human subject for 2s breath-hold at 90% exhalation position in each respiratory cycle and (2) the gated T2 weighted SPACE MR pulse sequence of 3 T Siemens MRI for 3D thoracic imaging. The improvement in the upper liver breath-hold motion reproducibility within the gating window using the QBH biofeedback system has been assessed for a group of volunteers. Each subject underwent two imaging sessions for the assessments of the residual respiratory motion management within the gating window and respiratory motion artifacts in 3D thoracic MRI both with/without QBH biofeedback. The residual upper liver motion within the gating window during MR acquisitions (∼6 minutes) has been considerably reduced using QBH biofeedback, resulting in the reduction of respiratory motion artifacts in lungs and liver of 3D thoracic MR images. Additionally, average RMSE (root mean square error) of abdomen displacement obtained from the RPM has been reduced from 2.3mm of free breathing to 0.8mm of QBH biofeedback breathing: 65% of average displacement error reduction with QBH biofeedback. The study demonstrated the improvement of the upper liver breath-hold motion reproducibility using QBH biofeedback during 3D thoracic MR imaging. This system can provide clinically applicable motion management of the internal anatomy for gated radiotherapy.
The aim of the study is to test a hypothesis that quasi-breath-hold (QBH) biofeedback improves th... more The aim of the study is to test a hypothesis that quasi-breath-hold (QBH) biofeedback improves the residual respiratory motion management in gated 3D thoracic MR imaging, reducing respiratory motion artifacts with insignificant acquisition time alteration. To test the hypothesis five healthy human subjects underwent two gated MR imaging studies based on a T2 weighted SPACE MR pulse sequence using a respiratory navigator of a 3T Siemens MRI: one under free breathing and the other under QBH biofeedback breathing. The QBH biofeedback system utilized the external marker position on the abdomen obtained with an RPM system (Real-time Position Management, Varian) to audiovisually guide a human subject for 2s breath-hold at 90% exhalation position in each respiratory cycle. The improvement in the upper liver breath-hold motion reproducibility within the gating window using the QBH biofeedback system has been assessed for a group of volunteers. We assessed the residual respiratory motion management within the gating window and respiratory motion artifacts in 3D thoracic MRI both with/without QBH biofeedback. In addition, the RMSE (root mean square error) of abdominal displacement has been investigated. The QBH biofeedback reduced the residual upper liver motion within the gating window during MR acquisitions (∼6 minutes) compared to that for free breathing, resulting in the reduction of respiratory motion artifacts in lung and liver of gated 3D thoracic MR images. The abdominal motion reduction in the gated window was consistent with the residual motion reduction of the diaphragm with QBH biofeedback. Consequently, average RMSE (root mean square error) of abdominal displacement obtained from the RPM has been also reduced from 2.0 mm of free breathing to 0.7 mm of QBH biofeedback breathing over the entire cycle (67% reduction, p-value=0.02) and from 1.7 mm of free breathing to 0.7 mm of QBH biofeedback breathing in the gated window (58% reduction, p-value=0.14). The average baseline drift obtained using a linear fit was reduced from 5.5 mm/min with free breathing to 0.6 mm/min (89% reduction, p-value=0.017) with QBH biofeedback. The study demonstrated that the QBH biofeedback improved the upper liver breath-hold motion reproducibility during the gated 3D thoracic MR imaging. This system can provide clinically applicable motion management of the internal anatomy for gated medical imaging as well as gated radiotherapy.
The accuracy of motion prediction, utilized to overcome the system latency of motion management r... more The accuracy of motion prediction, utilized to overcome the system latency of motion management radiotherapy systems, is hampered by irregularities present in the patients' respiratory pattern. Audiovisual (AV) biofeedback has been shown to reduce respiratory irregularities. The aim of this study was to test the hypothesis that AV biofeedback improves the accuracy of motion prediction. Methods: An AV biofeedback system combined with real-time respiratory data acquisition and MR images were implemented in this project. One-dimensional respiratory data from (1) the abdominal wall (30 Hz) and (2) the thoracic diaphragm (5 Hz) were obtained from 15 healthy human subjects across 30 studies. The subjects were required to breathe with and without the guidance of AV biofeedback during each study. The obtained respiratory signals were then implemented in a kernel density estimation prediction algorithm. For each of the 30 studies, five different prediction times ranging from 50 to 1400 ms were tested (150 predictions performed). Prediction error was quantified as the root mean square error (RMSE); the RMSE was calculated from the difference between the real and predicted respiratory data. The statistical significance of the prediction results was determined by the Student's t-test. Results: Prediction accuracy was considerably improved by the implementation of AV biofeedback. Of the 150 respiratory predictions performed, prediction accuracy was improved 69% (103/150) of the time for abdominal wall data, and 78% (117/150) of the time for diaphragm data. The average reduction in RMSE due to AV biofeedback over unguided respiration was 26% (p < 0.001) and 29% (p < 0.001) for abdominal wall and diaphragm respiratory motion, respectively. Conclusions: This study was the first to demonstrate that the reduction of respiratory irregularities due to the implementation of AV biofeedback improves prediction accuracy. This would result in increased efficiency of motion management techniques affected by system latencies used in radiotherapy.
In-room Magnetic Resonance Imaging (MRI) allows the acquisition of fast 2D cine-18 MRI centered i... more In-room Magnetic Resonance Imaging (MRI) allows the acquisition of fast 2D cine-18 MRI centered in the tumor for advanced motion management in radiotherapy. To 19 achieve 3D information during treatment, patient-specific motion models can be 20 considered the most viable solution. However, conventional global motion models are 21 built using a single motion surrogate, independently from the anatomical location. 22 In this work, we present a novel motion model based on regions of interest (ROIs) 23 established on 4D Computed Tomography (4DCT) and 2D cine-MRI, aiming at 24 accurately compensating for changes during treatment. In the planning phase, a 25 motion model is built on a 4DCT dataset, through 3D deformable image registration 26 (DIR). ROIs are then defined and correlated with motion fields derived by 2D DIR 27 between CT slices centered in the tumor. In the treatment phase, the model is applied 28 to in-room cine-MRI data to compensate for organ motion in a multi-modal framework, 29 aiming at estimating a time-resolved 3DCT. 30 The method is validated on a digital phantom and tested on two lung patients. Analysis 31 is performed by considering different anatomical planes (coronal, sagittal and a 32 combination of the two) and evaluating the performance of the method on tumor and 33 diaphragm. For the phantom study, the ROI-based model results in a uniform median 34 error on both diaphragm and tumor below 1.5mm. For what concerns patients, median 35 errors on both diaphragm and tumor are around 2mm (maximum patient resolution), 36 confirming the capability of the method to regionally compensate for motion. 37 A novel ROI-based motion model is proposed as an integral part of an envisioned 38 clinical MRI-guided workflow aiming at enhanced image guidance compared to 39 conventional strategies. 40 41 *
ESTRO 35 2016 S73 _______________________________________________________________________________... more ESTRO 35 2016 S73 ______________________________________________________________________________________________________ centroid coordinates and the detected location was larger than 2.7mm in plane and 3mm in slice direction. Results: Table1 shows the average AUC values for the model results of all patients using a single sequence and when combined. The combined model (AUC=0.94) performs significantly better than the best imaging sequence alone (T1-THRIVE AUC=0.84). Without post-processing the model correctly identifies 80/86 markers but with a total of 98 FP. After post-processing, we reduced the FP to a total of 20 but the true positives (TP) were also reduced to 66. Figure 1 shows the model pipeline. Deviations between the reference and the correctly identified marker location are < 1mm.
In lung radiotherapy, variations in cycle-to-cycle breathing results in four-dimensional computed... more In lung radiotherapy, variations in cycle-to-cycle breathing results in four-dimensional computed tomography imaging artifacts, leading to inaccurate beam coverage and tumor targeting. In previous studies, the effect of audiovisual (AV) biofeedback on the external respiratory signal reproducibility has been investigated but the internal anatomy motion has not been fully studied. The aim of this study is to test the hypothesis that AV biofeedback improves diaphragm motion reproducibility of internal anatomy using magnetic resonance imaging (MRI). Methods: To test the hypothesis 15 healthy human subjects were enrolled in an ethics-approved AV biofeedback study consisting of two imaging sessions spaced ∼1 week apart. Within each session MR images were acquired under free breathing and AV biofeedback conditions. The respiratory signal to the AV biofeedback system utilized optical monitoring of an external marker placed on the abdomen. Synchronously, serial thoracic 2D MR images were obtained to measure the diaphragm motion using a fast gradient-recalled-echo MR pulse sequence in both coronal and sagittal planes. The improvement in the diaphragm motion reproducibility using the AV biofeedback system was quantified by comparing cycle-to-cycle variability in displacement, respiratory period, and baseline drift. Additionally, the variation in improvement between the two sessions was also quantified. Results: The average root mean square error (RMSE) of diaphragm cycle-to-cycle displacement was reduced from 2.6 mm with free breathing to 1.6 mm (38% reduction) with the implementation of AV biofeedback (p-value < 0.0001). The average RMSE of the respiratory period was reduced from 1.7 s with free breathing to 0.3 s (82% reduction) with AV biofeedback (p-value < 0.0001). Additionally, the average baseline drift obtained using a linear fit was reduced from 1.6 mm/min with free breathing to 0.9 mm/min (44% reduction) with AV biofeedback (p-value = 0.012). The diaphragm motion reproducibility improvements with AV biofeedback were consistent with the abdominal motion reproducibility that was observed from the external marker motion variation. Conclusions: This study was the first to investigate the potential of AV biofeedback to improve the motion reproducibility of internal anatomy using MRI. The study demonstrated the significant improvement in diaphragm motion reproducibility using AV biofeedback combined with MRI. This system can potentially provide clinically beneficial motion management of internal anatomy in MRI and radiotherapy.
The use of trajectory log files for routine patient quality assurance is gaining acceptance. Such... more The use of trajectory log files for routine patient quality assurance is gaining acceptance. Such use requires the validation of the trajectory log itself. However, the accurate localization of a multileaf collimator (MLC) leaf while it is in motion remains a challenging task. We propose an efficient phantom-less technique using the EPID to verify the dynamic MLC positions with high accuracy. Measurements were made on four Varian TrueBeams equipped with M120 MLCs. Two machines were equipped with the S1000 EPID; two were equipped with the S1200 EPID. All EPIDs were geometrically corrected prior to measurements. Dosimetry mode EPID measurements were captured by a frame grabber card directly linked to the linac. All leaf position measurements were corrected both temporally and geometrically. The readout latency of each panel, as a function of pixel row, was determined using a 40 × 1.0 cm 2 sliding window (SW) field moving at 2.5 cm/s orthogonal to the row readout direction. The latency of each panel type was determined by averaging the results of two panels of the same type. Geometric correction was achieved by computing leaf positions with respect to the projected isocenter position as a function of gantry angle. This was determined by averaging the central axis position of fields at two collimator positions of 90°and 270°. The radiological to physical leaf end position was determined by comparison of the measured gap with that determined using a feeler gauge. The radiological to physical leaf position difference was found to be 0.1 mm. With geometric and latency correction, the proposed method was found to be improve the ability to detect dynamic MLC positions from 1.0 to 0.2 mm for all leaves. Latency and panel residual geometric error correction improve EPID-based MLC position measurement. These improvements provide for the first time a trajectory log QA procedure.
Pearson's linear correlation coefficient). MHW Heart was retained as MHD surrogate. MHW Heart = 1... more Pearson's linear correlation coefficient). MHW Heart was retained as MHD surrogate. MHW Heart = 1.5 cm was found to be the most optimal threshold to identify patients with MHD > 3.5 Gy (Y = 1.705). These results lead to the development of the DIBH decision-making procedure: 1) single CT-slice acquisition (Figure (b)), 2) projection of the mean medial field setup, 3) MHW measurement and 4) DIBH decision-making. This procedure was found to have a sensitivity of 87.5% and a specificity of 90.9%. Patients stratified to FB-WBRT (10/30) had a clinically acceptable average MHD: 2.8 ± 1.4 Gy (range: 1.0-5.3 Gy). Patients stratified to DIBH-WBRT (20/30) had significantly higher average MHD during FB-WBRT: 6.5 ± 2.6 Gy (range: 2.9-11.1 Gy) (p < 0.001, t-test), indeed needing MHD reduction. Conclusions: DIBH decision-making based on single CT-slice acquisition is feasible in left-sided WBRT. It is followed by the acquisition of 1 CT-scan, during FB or DIBH. The proposed procedure therefore halves the workload of DIBH decisionmaking during treatment planning.
The use of super-paramagnetic iron oxide nanoparticles (SPIONs) as an MRI contrast agent (SPION-C... more The use of super-paramagnetic iron oxide nanoparticles (SPIONs) as an MRI contrast agent (SPION-CA) can safely label hepatic macrophages and be localized within hepatic parenchyma for T2*- and R2*-MRI of the liver. To date, no study has utilized the R2*-MRI with SPIONs for quantifying liver heterogeneity to characterize functional liver parenchyma (FLP) and hepatic tumors. This study investigates whether SPIONs enhance liver heterogeneity for an auto-contouring tool to identify the voxel-wise functional liver parenchyma volume (FLPV). This was the first study to directly evaluate the impact of SPIONs on the FLPV in R2*-MRI for 12 liver cancer patients. By using SPIONs, liver heterogeneity was improved across pre- and post-SPION MRI sessions. On average, 60% of the liver [range 40–78%] was identified as the FLPV in our auto-contouring tool with a pre-determined threshold of the mean R2* of the tumor and liver. This method performed well in 10 out of 12 liver cancer patients; the rema...
Journal of medical imaging and radiation oncology, 2018
In-room MRI is a promising image guidance strategy in external beam radiotherapy to acquire volum... more In-room MRI is a promising image guidance strategy in external beam radiotherapy to acquire volumetric information for moving targets. However, limitations in spatio-temporal resolution led several authors to use 2D orthogonal images for guidance. The aim of this work is to present a method to concurrently compensate for non-rigid tumour motion and provide an approach for 3D reconstruction from 2D orthogonal cine-MRI slices for MRI-guided treatments. Free-breathing sagittal/coronal interleaved 2D cine-MRI were acquired in addition to a pre-treatment 3D volume in two patients. We performed deformable image registration (DIR) between cine-MRI slices and corresponding slices in the pre-treatment 3D volume. Based on an extrapolation of the interleaved 2D motion fields, the 3D motion field was estimated and used to warp the pre-treatment volume. Due to the lack of a ground truth for patients, the method was validated on a digital 4D lung phantom. On the phantom, the 3D reconstruction met...
Several image-based retrospective sorting methods of 4D magnetic resonance imaging (4D MRI) have ... more Several image-based retrospective sorting methods of 4D magnetic resonance imaging (4D MRI) have been proposed for respiratory motion reconstruction in external beam radiotherapy. However, the optimal strategy for providing accurate and artifact-free 4D MRI, ideally corresponding to an average breathing cycle, is not yet defined. This study presents a proactive comparison of three published image-based sorting methods, to define a groundwork for benchmarking in 4D MRI. Three published 4D MRI methods were selected for image retrospective sorting: body area, mutual information, and navigator slice. The three image-based methods were compared against a conventional retrospective sorting method based on an external surrogate. Comparisons were performed by means of an MRI digital phantom, derived from the XCAT CT phantom generated with different patient-derived signals, for a total of 12 cases. Specific multislice MRI acquisitions were simulated for slice sorting and sagittal, coronal, a...
Breathing management can reduce breath-to-breath (intrafraction) and day-by-day (interfraction) v... more Breathing management can reduce breath-to-breath (intrafraction) and day-by-day (interfraction) variability in breathing motion while utilizing the respiratory motion of internal and external surrogates for respiratory guidance. Audiovisual (AV) biofeedback, an interactive personalized breathing motion management system, has been developed to improve reproducibility of intra- and interfraction breathing motion. However, the assumption of the correlation of respiratory motion between surrogates and tumors is not always verified during medical imaging and radiation treatment. Therefore, the aim of the study was to test the hypothesis that the correlation of respiratory motion between surrogates and tumors is the same under free breathing without guidance (FB) and with AV biofeedback guidance for voluntary motion management. For 13 lung cancer patients receiving radiotherapy, 2D coronal and sagittal cine-MR images were acquired across two MRI sessions (pre- and mid-treatment) with two ...
Australasian Physical & Engineering Sciences in Medicine, 2014
This study evaluated if an audiovisual (AV) biofeedback causes variation in the level of external... more This study evaluated if an audiovisual (AV) biofeedback causes variation in the level of external and internal correlation due to its interactive intervention in natural breathing. The internal (diaphragm) and external (abdominal wall) respiratory motion signals of 15 healthy human subjects under AV biofeedback and free breathing (FB) were analyzed and measures of correlation and regularity taken. Regularity metrics (root mean square error and spectral power dispersion metric) were obtained and the correlation between these metrics and the internal and external correlation was investigated. For FB and AV biofeedback assisted breathing the mean correlations found between internal and external respiratory motion were 0.96 ± 0.02 and 0.96 ± 0.03, respectively. This means there is no evidence to suggest (p-value = 0.88) any difference in the correlation between internal and external respiratory motion with the use of AV biofeedback. Our results confirmed the hypothesis that the internal-external correlation with AV biofeedback is the same as for free breathing. Should this correlation be maintained for patients, AV biofeedback can be implemented in the clinic with confidence as regularity improvements using AV biofeedback with an external signal will be reflected in increased internal motion regularity.
Innovation/Impact: We propose a dynamic keyhole method for MR image reconstruction using respirat... more Innovation/Impact: We propose a dynamic keyhole method for MR image reconstruction using respiratory external/internal surrogate motion for real-time tumor monitoring in image guided radiotherapy (IGRT). Using dynamic keyhole method with 47 datasets eliminates the known artifacts while retaining high image quality for shorter acquisition times.
International Journal of Radiation Oncology*Biology*Physics, 2016
To assess the impact of an audiovisual (AV) biofeedback on intra-and interfraction tumor motion f... more To assess the impact of an audiovisual (AV) biofeedback on intra-and interfraction tumor motion for lung cancer patients. Methods and Materials Lung tumor motion was investigated in 9 lung cancer patients who underwent a breathing training session with AV biofeedback before 2 3T magnetic resonance imaging (MRI) sessions. The breathing training session was performed to allow patients to become familiar with AV biofeedback, which uses a guiding wave customized for each patient according to a reference breathing pattern. In the first MRI session (pretreatment), 2-dimensional cine-MR images with (1) free breathing (FB) and (2) AV biofeedback were obtained, and the second MRI session was repeated within 3-6 weeks (mid-treatment). Lung tumors were directly measured from cine-MR images using an auto-segmentation technique; the centroid and outlier motions of the lung tumors were measured from the segmented tumors. Free breathing and AV biofeedback were compared using several metrics: intra-and interfraction tumor motion consistency in displacement and period, and the outlier motion ratio. Results Compared with FB, AV biofeedback improved intrafraction tumor motion consistency by 34% in displacement (P=.019) and by 73% in period (P<.001). Compared with FB, AV biofeedback improved interfraction tumor motion consistency by 42% in displacement (P<.046) and by 74% in period (P=.005). Compared with FB, AV biofeedback reduced the outlier motion ratio by 21% (P<.001). Conclusions These results demonstrated that AV biofeedback significantly improved intra-and interfraction lung tumor motion consistency for lung cancer patients. These results demonstrate that AV biofeedback can facilitate consistent tumor motion, which is advantageous toward achieving more accurate medical imaging and radiation therapy procedures. * Paired Student t test between FB and AV biofeedback (coronal and sagittal together).
Journal of Medical Imaging and Radiation Oncology, 2019
Introduction 4D-MRI, compared to 4D-CT, provides better soft-tissue contrast for target delineati... more Introduction 4D-MRI, compared to 4D-CT, provides better soft-tissue contrast for target delineation. However, motion artefacts are often observed due to residual breathing variations. This study is to present a retrospective 4D-MRI reconstruction method based on 2D diaphragm profiles to improve the quality of 4D-MR images in the presence of significant breathing variations. Methods The proposed 4D-MRI reconstruction method utilized diaphragm profiles (2D cine images on a single sagittal plan at the peak diaphragm) in conjunction with 4D-MR scans (2D-cine images on multiple predetermined coronal planes along the anterior-posterior direction over a volume of interest). The diaphragm profile images were exploited to sort the 4D-MR scans by matching respiratory amplitude of diaphragm on the 4D-MR scans to the diaphragm profiles. To evaluate reconstructed 4D-MR images (ten 3D-MR images), sagittal images on ten 3D-MR images under free breathing (FB) and respiratory guidance (GB) were compared with diaphragm profile images (reference) from 13 healthy volunteers. Results Forty-four 4D-MR scan datasets were successfully reconstructed without distinct respiratory-related motion artefacts even with the presence of breathing variation. The differences in diaphragm profiles between the reference and corresponding reconstructed images in the mean of root mean square were similar between FB (3.5 mm) and GB (3.0 mm), confirming that the 4D-MRI reconstruction method was effective even with significant breathing variation. Conclusions The diaphragm profiles were utilized to reconstruct 4D-MR images with spatial reliability and a fixed scan time under FB and GB. Our method can provide reliable 4D information of thoracic and abdominal regions for MRI-guided radiotherapy.
Respiratory variation can increase the variability of tumor position and volume, accounting for l... more Respiratory variation can increase the variability of tumor position and volume, accounting for larger treatment margins and longer treatment times. Audiovisual biofeedback as a breath-hold technique could be used to improve the reproducibility of lung tumor positions at inhalation and exhalation for the radiation therapy of mobile lung tumors. This study aimed to assess the impact of audiovisual biofeedback breath-hold (AVBH) on interfraction lung tumor position reproducibility and volume consistency for respiratory-gated lung cancer radiation therapy. Methods: Lung tumor position and volume were investigated in 9 patients with lung cancer who underwent a breath-hold training session with AVBH before 2 magnetic resonance imaging (MRI) sessions. During the first MRI session (before treatment), inhalation and exhalation breath-hold 3dimensional MRI scans with conventional breath-hold (CBH) using audio instructions alone and AVBH were acquired. The second MRI session (midtreatment) was repeated within 6 weeks after the first session. Gross tumor volumes (GTVs) were contoured on each dataset. CBH and AVBH were compared in terms of tumor position reproducibility as assessed by GTV centroid position Sources of support: This study was supported by an NHMRC Australia Fellowship.
The dynamic keyhole is a new MR image reconstruction method for thoracic and abdominal MR imaging... more The dynamic keyhole is a new MR image reconstruction method for thoracic and abdominal MR imaging. To date, this method has not been investigated with cancer patient MRI data. The goal of this study was to assess the dynamic keyhole method for the task of lung tumor localization using cine-MR images reconstructed in the presence of respiratory motion. Methods: The dynamic keyhole method utilizes a previously acquired a library of peripheral k-space datasets at similar displacement and phase (where phase is simply used to determine whether the breathing is inhale to exhale or exhale to inhale) respiratory bins in conjunction with central k-space datasets (keyhole) acquired. External respiratory signals drive the process of sorting, matching and combining the two k-space streams for each respiratory bin, thereby achieving faster image acquisition without substantial motion artifacts. This study was the first that investigates the impact of k-space undersampling on lung tumor motion and area assessment across clinically available techniques (zero-filling and conventional keyhole). In this study, the dynamic 2 keyhole, conventional keyhole and zero-filling methods were compared to full k-space dataset acquisition by quantifying (1) keyhole size required for central k-space datasets for constant image quality across sixty four cine-MRI datasets from nine lung cancer patients, (2) the intensity difference between the original and reconstructed images in a constant keyhole size, and (3) the accuracy of tumor motion and area directly measured by tumor auto-contouring. Results: For constant image quality, the dynamic keyhole method, conventional keyhole and zero-filling methods required 22%, 34% and 49% of the keyhole size (P < 0.0001), respectively, compared to the full kspace image acquisition method. Compared to the conventional keyhole and zero-filling reconstructed images with the keyhole size utilized in the dynamic keyhole method, an average intensity difference of the dynamic keyhole reconstructed images (P < 0.0001) was minimal, and resulted in the accuracy of tumor motion within 99.6% (P < 0.0001) and the accuracy of tumor area within 98.0% (P < 0.0001) for lung tumor monitoring applications. Conclusions: This study demonstrates that the dynamic keyhole method is a promising technique for clinical applications such as image-guided radiation therapy requiring the MR monitoring of thoracic tumors. Based on the results from this study, the dynamic keyhole method could increase the imaging frequency by up to a factor of five compared with full k-space methods for real-time lung tumor MRI.
The aim of the project is to test the hypothesis that quasi-breath-hold (QBH) biofeedback improve... more The aim of the project is to test the hypothesis that quasi-breath-hold (QBH) biofeedback improves the residual respiratory motion management within a gating window, reducing respiratory motion artifacts in gated 3D thoracic MR images. A QBH biofeedback system has been employed with gated 3D thoracic MRI acquisitions. The QBH biofeedback system utilized (1) the external marker position on the abdomen using an RPM system (Real-time Position Management, Varian) to audio-visually guide a human subject for 2s breath-hold at 90% exhalation position in each respiratory cycle and (2) the gated T2 weighted SPACE MR pulse sequence of 3 T Siemens MRI for 3D thoracic imaging. The improvement in the upper liver breath-hold motion reproducibility within the gating window using the QBH biofeedback system has been assessed for a group of volunteers. Each subject underwent two imaging sessions for the assessments of the residual respiratory motion management within the gating window and respiratory motion artifacts in 3D thoracic MRI both with/without QBH biofeedback. The residual upper liver motion within the gating window during MR acquisitions (∼6 minutes) has been considerably reduced using QBH biofeedback, resulting in the reduction of respiratory motion artifacts in lungs and liver of 3D thoracic MR images. Additionally, average RMSE (root mean square error) of abdomen displacement obtained from the RPM has been reduced from 2.3mm of free breathing to 0.8mm of QBH biofeedback breathing: 65% of average displacement error reduction with QBH biofeedback. The study demonstrated the improvement of the upper liver breath-hold motion reproducibility using QBH biofeedback during 3D thoracic MR imaging. This system can provide clinically applicable motion management of the internal anatomy for gated radiotherapy.
The aim of the study is to test a hypothesis that quasi-breath-hold (QBH) biofeedback improves th... more The aim of the study is to test a hypothesis that quasi-breath-hold (QBH) biofeedback improves the residual respiratory motion management in gated 3D thoracic MR imaging, reducing respiratory motion artifacts with insignificant acquisition time alteration. To test the hypothesis five healthy human subjects underwent two gated MR imaging studies based on a T2 weighted SPACE MR pulse sequence using a respiratory navigator of a 3T Siemens MRI: one under free breathing and the other under QBH biofeedback breathing. The QBH biofeedback system utilized the external marker position on the abdomen obtained with an RPM system (Real-time Position Management, Varian) to audiovisually guide a human subject for 2s breath-hold at 90% exhalation position in each respiratory cycle. The improvement in the upper liver breath-hold motion reproducibility within the gating window using the QBH biofeedback system has been assessed for a group of volunteers. We assessed the residual respiratory motion management within the gating window and respiratory motion artifacts in 3D thoracic MRI both with/without QBH biofeedback. In addition, the RMSE (root mean square error) of abdominal displacement has been investigated. The QBH biofeedback reduced the residual upper liver motion within the gating window during MR acquisitions (∼6 minutes) compared to that for free breathing, resulting in the reduction of respiratory motion artifacts in lung and liver of gated 3D thoracic MR images. The abdominal motion reduction in the gated window was consistent with the residual motion reduction of the diaphragm with QBH biofeedback. Consequently, average RMSE (root mean square error) of abdominal displacement obtained from the RPM has been also reduced from 2.0 mm of free breathing to 0.7 mm of QBH biofeedback breathing over the entire cycle (67% reduction, p-value=0.02) and from 1.7 mm of free breathing to 0.7 mm of QBH biofeedback breathing in the gated window (58% reduction, p-value=0.14). The average baseline drift obtained using a linear fit was reduced from 5.5 mm/min with free breathing to 0.6 mm/min (89% reduction, p-value=0.017) with QBH biofeedback. The study demonstrated that the QBH biofeedback improved the upper liver breath-hold motion reproducibility during the gated 3D thoracic MR imaging. This system can provide clinically applicable motion management of the internal anatomy for gated medical imaging as well as gated radiotherapy.
The accuracy of motion prediction, utilized to overcome the system latency of motion management r... more The accuracy of motion prediction, utilized to overcome the system latency of motion management radiotherapy systems, is hampered by irregularities present in the patients' respiratory pattern. Audiovisual (AV) biofeedback has been shown to reduce respiratory irregularities. The aim of this study was to test the hypothesis that AV biofeedback improves the accuracy of motion prediction. Methods: An AV biofeedback system combined with real-time respiratory data acquisition and MR images were implemented in this project. One-dimensional respiratory data from (1) the abdominal wall (30 Hz) and (2) the thoracic diaphragm (5 Hz) were obtained from 15 healthy human subjects across 30 studies. The subjects were required to breathe with and without the guidance of AV biofeedback during each study. The obtained respiratory signals were then implemented in a kernel density estimation prediction algorithm. For each of the 30 studies, five different prediction times ranging from 50 to 1400 ms were tested (150 predictions performed). Prediction error was quantified as the root mean square error (RMSE); the RMSE was calculated from the difference between the real and predicted respiratory data. The statistical significance of the prediction results was determined by the Student's t-test. Results: Prediction accuracy was considerably improved by the implementation of AV biofeedback. Of the 150 respiratory predictions performed, prediction accuracy was improved 69% (103/150) of the time for abdominal wall data, and 78% (117/150) of the time for diaphragm data. The average reduction in RMSE due to AV biofeedback over unguided respiration was 26% (p < 0.001) and 29% (p < 0.001) for abdominal wall and diaphragm respiratory motion, respectively. Conclusions: This study was the first to demonstrate that the reduction of respiratory irregularities due to the implementation of AV biofeedback improves prediction accuracy. This would result in increased efficiency of motion management techniques affected by system latencies used in radiotherapy.
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Papers by Danny Lee