Irregular Breathing Research Articles

P203] WEPL-corrected margins for moving targets in carbon-ion gated treatments: Preliminary results

Purpose To evaluate intra- and inter-fractional robustness of carbon-ion treatment plans based on water-equivalent path length (WEPL) corrected ITV margins for moving targets irradiated with gated pencil-beam scanning. Methods As a preliminary study, three patients with thoraco-abdominal targets were considered. Clinical plans were optimized with an Intensity Modulated Particle Therapy (IMPT) algorithm and the use of case-specific avoidance structures to prevent radiation pathways on regions subject to intra- and inter-fractional variations. Plans were optimized on the end-exhale CT of a 4DCT dataset using 2 fields and tested for consistency within the gating window by recalculation on the 30%-exhale and 30%-inhale CTs. Single Field Uniform Dose (SFUD) plans were optimized on beam-specific WEPL-corrected ITV ( ITV WEPL ), which comprised the envelope of water-equivalent target positions within the ideal gating window. Differently from clinical plans, avoidance structures were not used in this approach. Clinical plans were taken as reference for comparison. Dose recalculations on the planning 4DCT and on synthetic 4DCT simulating irregular breathing allowed to evaluate intra-fractional robustness of the two approaches, whereas inter-fractional robustness was estimated on re-evaluation CTs (one per patient). Differences in the conformity index CI = V 95 % / V target , target coverage D 95 % and homogeneity index HI = ( D 2 % − D 98 % )/ D 50 % between the end-exhale plan and the recalculated dose distributions were computed. Doses to the involved organs at risk (OARs) were evaluated as well. Results The CI presented slightly higher median intra-/inter-fractional variations and absolute values in the ITV WEPL approach (13%–1.47) with respect to reference plans (6%–1.36). D 95 % and HI showed lower median intra-fractional variations for the ITV WEPL approach (0.1% and 35%) compared to reference plans (3.4% and 46%). In case of inter-fractional changes, the use of ITV WEPL led to higher median variations but comparable absolute values for D 95 % (3.8% vs 2.2%) and for HI (144% vs 20%, absolute median values: 0.11 vs 0.14). The two methods performed similarly in OARs. Conclusions The use of WEPL-corrected ITV permits adequate tumor coverage even in presence of irregular breathing motion, for the small analyzed sample. Although uncertainties due only to intra-fractional organ motion were considered in the ITV WEPL approach, comparable inter-fractional robustness was found among the two strategies.

An in silico performance characterization of respiratory motion guided 4DCT for high-quality low-dose lung cancer imaging

This work aims to characterize the performance of an improved 4DCT technique aiming to overcome irregular breathing-related image artifacts. To address this, we have developed respiratory motion guided (RMG) 4DCT, which uses real-time breathing motion analysis to prospectively gate scans based on detection of irregular breathing. This is the first investigation of RMG-4DCT using a real-time software prototype, testing the hypothesis that it can reduce breathing irregularities during imaging, reduce image oversampling and improve image quality compared to a ‘conventional’ 4DCT protocol without breathing guidance. RMG-4DCT scans were simulated based on 100+ hours of breathing motion acquired for 20 lung cancer patients. Scan performance was quantified in terms of the beam on time (a surrogate for imaging dose), total scan time and the breathing irregularity during imaging (via RMSE of the breathing motion during acquisition). A conventional 4DCT protocol was also implemented using the same software prototype for a direct comparator to the RMG-4DCT results. We investigated the impact of key RMG-4DCT parameters such as gating tolerance, gantry rotation time and the use of baseline drift correction. Using a representative set of algorithm parameters, RMG-4DCT achieved significant mean reductions in estimated imaging dose (−17.8%, p < 0.001) and breathing RMSE during imaging (−12.6%, p < 0.001) compared to conventional 4DCT. These improvements came with increased scan times, roughly doubled on average (104%, p < 0.001). Image quality simulations were performed using the deformable digital XCAT phantom, with image quality quantified based on the normalized cross correlation (NCC) between axial slices. RMG-4DCT demonstrated qualitative image quality improvements for three out of 10 phase bins, however the improvement was not significant across all 10 phases (p = 0.08) at a population level. In choosing RMG-4DCT scan parameters, the trade-off between gating sensitivity and scan time may be optimized, demonstrating potential for RMG-4DCT as a viable pathway to improve clinical 4DCT imaging.

A phantom study to create synthetic CT from orthogonal twodimensional cine MRI and evaluate the effect of irregular breathing.

An exciting innovation in radiotherapy is the use of real-time MRI for treatment adaptation. This study proposes an in-silico framework for the generation of 3D synthetic CT (sCT) from orthogonal interleaved 2D cine MRI data to overcome the lack of electron density information in MR images. The method uses pre-treatment data to build a patient breathing motion model. This model is then driven by surrogates extracted from cine MR images during the treatment. The effect of irregular breathing on the motion model is also evaluated by simulating different motion components related to uncorrelated diaphragm, chest and tumor motion. 3D sCT were successfully created for each of the 512 cine MRI pairs in the digital phantom study. The analysis showed that the diaphragm position was a good surrogate to rescale the 3D breathing motion for the current regular breathing phase. However, respiratory and tumor motion were correlated in only 59% of the phases, resulting in tumor position uncertainties of up to 3mm. The inclusion of additional chest and tumor motion information improved the accuracy for irregular changes in breathing pattern and enhanced the tumor position uncertainties to less than 1mm. This study successfully demonstrated a proof-ofprinciple for a digital phantom dataset based on patient parameters, providing a way to create real-time 3D electron density volumes and enhancing the need to account for irregular breathing pattern.

The effect of mechanical or electrical stimulation on apnea length in mice.

Premature birth is a leading cause of infant mortality which is often attributed to irregular breathing and apnea of prematurity. A common treatment for apnea is caffeine to stimulate the brain's respiratory center. However, caffeine's long term effect on infant development is not fully comprehended. We hypothesized that noninvasive localized body stimulation regularizes breathing pattern. We investigated the impact of electrical or mechanical stimulation on breathing in mice. After the mice were ventilated for 28s to induce apnea, mice were taken off the ventilator while receiving mechanical, electrical, or no stimulation in a randomized order. Both stimuli targeted the diaphragm area through a custom-built belt with vibrating motors or adhesive electrodes. After each apnea cycle, the time to take the first breath (T) was recorded. The electrical stimulation given at 4.5, 8.3, 16.7V (pulse rate = 3Hz, pulse width = 120μs) showed no reduction in T. Electrical stimulation at pulse rates of 10 or 20Hz (16.7V, pulse width 260μs) showed a detrimental effect increasing T by ~ 7% compared to control values (p = 0.005, p = 0.038 respectively). High and medium intensity mechanical stimulations significantly reduced T by 11.74 (p < 10-13) and by 17.08% (p < 10-8), respectively. Further reducing the amplitude of vibrations did not affect T. When the probe was attached to the ankles, only the high intensity vibrations resulted in a decrease in T (p < 10-13). Mechanical vibrations, applied at various intensities and locations, could be used to treat irregular breathing and apnea in infants.

Performance Evaluation of the Tumor Tracking Method Using Beam on/off Interface for the Treatment of Irregular Breathing

Dose rate regulated tracking is known to be an efficient method which adaptively delivers tracking treatments when patient breathing is irregular. The Motion Management Interface (MMI, Varian Medical System, CA), which provides beam on/off switching during treatment is available for clinic. Study is to test if delivering the adaptive tumor tracking is feasible for irregular breathing using beam switching with MMI. 55 free breathing RPM traces acquired from lung cancer patients are used. The first day RPM traces of the patients are utilized to design preprogrammed tracking MLC patterns, of which periods are intentionally reduced by 20% in order to catch up the variation of patient breathing irregularity in the treatment day. Eligibility criteria for this technique are the variation of amplitude and period less than 20%. An algorithm which determines beam on/off every 100 ms by considering the preprogrammed (MLC) positions and current breathing positions is developed. Tracking error and delivery efficacy are calculated by simulating the beam-switching adaptive tracking from the RPM traces. Breathing patterns of 38 patients (70%) met the eligibility criteria. Tracking errors of all of the cases who meet the criteria are less than 2 mm (average 1.4 mm) and the average delivery efficacy was 71%. Those of rest of the cases are 1.9 mm and 48%. Adaptive tracking with beam switching is feasible if patient selection is based on the eligibility criteria.

Evaluation of the accuracy of the CyberKnife Synchrony™ Respiratory Tracking System using a plastic scintillator.

The Synchrony™ Respiratory Tracking System of the CyberKnife® Robotic Radiosurgery System (Accuray, Inc., Sunnyvale, CA, USA) enables real-time tracking of moving targets such as lung and liver tumors during radiotherapy. Although film measurements have been used for quality assurance of the tracking system, they cannot evaluate the temporal tracking accuracy. We have developed a verification system using a plastic scintillator that can evaluate the temporal accuracy of the CyberKnife Synchrony. A phantom consisting of a U-shaped plastic frame with three fiducial markers was used. The phantom was moved on a plastic scintillator plate. To identify the phantom position on the recording video in darkness, four pieces of fluorescent tape representing the corners of a 10cm×10cm square around an 8cm×8cm window were attached to the phantom. For a stable respiration model, the phantom was moved with the fourth power of a sinusoidal wave with breathing cycles of 4, 3, and 2s and an amplitude of 1cm. To simulate irregular breathing, the respiratory cycle was varied with Gaussian random numbers. A virtual target was generated at the center of the fluorescent markers using the MultiPlan™ treatment planning system. Photon beams were irradiated using a fiducial tracking technique. In a dark room, the fluorescent light of the markers and the scintillation light of the beam position were recorded using a camera. For each video frame, a homography matrix was calculated from the four fluorescent marker positions, and the beam position derived from the scintillation light was corrected. To correct the displacement of the beam position due to oblique irradiation angles and other systematic measurement errors, offset values were derived from measurements with the phantom held stationary. The average SDs of beam position measured without phantom motion were 0.16 and 0.20mm for lateral and longitudinal directions, respectively. For the stable respiration model, the tracking errors (mean±SD) were 0.40±0.64mm, -0.07±0.79mm, and 0.45±1.14mm for breathing cycles of 4, 3, and 2s, respectively. The tracking errors showed significant linear correlation with the phantom velocity. The correlation coefficients were 0.897, 0.913, and 0.957 for breathing cycles of 4, 3, and 2s, respectively. The unstable respiration model also showed linear correlation between tracking errors and phantom velocity. The probability of tracking error incidents increased with decreasing length of the respiratory cycles. Although the tracking error incidents increased with larger variations in respiratory cycle, the effect on the cumulative probability was insignificant. For a respiratory cycle of 4s, the maximum tracking error was 1.10 and 1.43mm at the probability of 10% and 5%, respectively. Large tracking errors were observed when there was phase shift between the tumor and the LED marker. This technique allows evaluation of the motion tracking accuracy of the Synchrony™ system over time by measurement of the photon beam. The velocity of the target and phase shift have significant effects on accuracy.

Breathing, Overbreathing, and Mindfulness

Overbreathing is one of the most common and yet overlooked breathing problems that people experience. A few irregular breaths can send us into a condition called hypocapnia, which leads to a variety of physiological, emotional, and behavioral consequences. The purpose of this paper is to review the physiology of breathing and overbreathing, discuss the impact of overbreathing on human physiology and behavior, review ways to recognize overbreathing, and discuss mindfulness-based skills that may be used to teach healthy breathing and correct overbreathing.

The Effects of Mirthful Laughter on Pain Tolerance and Delayed Onset Muscle Soreness.

Chronic pain is a debilitating disease that affects more people than any other chronic disease. Currently, there is not a singular treatment known to cure or assure relief from chronic pain. Accordingly, the management of patients’ discomfort is an integral part of treating chronic pain. Such treatment, however, is not effective for many patients. PURPOSE: We determined if mirthful laughter provided by comic relief can influence pain tolerance and muscle soreness in young healthy participants. METHODS: Forty participants underwent a randomized controlled cross-over designed experiment. Each participant was exposed to a comedy video eliciting mirthful laughter and a boring documentary. Delayed onset muscle soreness was induced in one leg at a time by eccentric exercises to mimic chronic pain. Pain tolerance was tested using the blunt force application. RESULTS: Watching the comedy video elicited a significantly greater irregular breathing pattern compared with watching the documentary video (p<0.001). After watching the comedy, the participants’ positive affect was increased (Δ2±1) while it was largely decreased (Δ-11±2) after watching the documentary video (p<0.001). Pain tolerance was decreased by 17±5 N after viewing the documentary video (p<0.001), but did not change significantly after watching the comedy. There were no significant changes in the visual analogue pain/soreness score from viewing either video. CONCLUSION: Thirty-minutes of watching a comedy eliciting laughter favorably influenced pain tolerance in healthy humans.

Tidal breath eNO measurements in a cohort of unsedated hospitalized neonates—A method validation

Exhaled Nitric oxide (eNO) is an inflammatory marker. In 2002 Hall et al. [J Appl Physiol. 92:59-66] established an infant eNO measurement method, fulfilling four criteria of feasibility: simple, non-invasive, without impact on the natural breathing pattern, and accounting for flow by NO output (V'NO). Although tidal breathing is accepted as an eNO measurement method in uncooperative patients, it is seldom used outside research labs. The variability and lack of validated methods have restrained from exploring the area in preterm and term neonates the last years. This study aimed to validate clinically feasible longitudinal online tidal eNO and V'NO in a real-life birth cohort of un-sedated, hospitalized preterm, and term neonates. We included 149 newborns, GA 28-42 weeks. Each scheduled for six repeated, non-invasive, on-line eNO measurements with Ecomedics CLD 88sp and NO-free air. We used three 60-second-eNO measurements. The method was adapted to fit preterm and term neonates with unstable respiration, without excluding sighs and surrounding breaths. Protocol measurements with a maximum mutual difference of 1 ppb succeeded in 85-99%, increasing with postnatal age. We performed mixed model analyses in three hierarchical measurement levels. Despite the irregular breathing of newborns, the predictions of individual eNO levels in the average infant was a 0.05 SD. Exhaled NO was flow-dependent (P = 0.028); V'NO but not eNO was associated with preterm birth (P < 0.001) and >24 h CPAP treatment (P = 0.0316). We validated clinically, non-invasive, online eNO measurements in neonates. The method was well tolerated and exhibited low subject-specific-prediction-variance and high success rates.

Optimized respiratory‐resolved motion‐compensated 3D Cartesian coronary MR angiography

PurposeTo develop a robust and efficient reconstruction framework that provides high‐quality motion‐compensated respiratory‐resolved images from free‐breathing 3D whole‐heart Cartesian coronary magnetic resonance angiography (CMRA) acquisitions.MethodsRecently, XD‐GRASP (eXtra‐Dimensional Golden‐angle RAdial Sparse Parallel MRI) was proposed to achieve 100% scan efficiency and provide respiratory‐resolved 3D radial CMRA images by exploiting sparsity in the respiratory dimension. Here, a reconstruction framework for Cartesian CMRA imaging is proposed, which provides respiratory‐resolved motion‐compensated images by incorporating 2D beat‐to‐beat translational motion information to increase sparsity in the respiratory dimension. The motion information is extracted from interleaved image navigators and is also used to compensate for 2D translational motion within each respiratory phase. The proposed Optimized Respiratory‐resolved Cartesian Coronary MR Angiography (XD‐ORCCA) method was tested on 10 healthy subjects and 2 patients with cardiovascular disease, and compared against XD‐GRASP.ResultsThe proposed XD‐ORCCA provides high‐quality respiratory‐resolved images, allowing clear visualization of the right and left coronary arteries, even for irregular breathing patterns. Compared with XD‐GRASP, the proposed method improves the visibility and sharpness of both coronaries. Significant differences (p < .05) in visible vessel length and proximal vessel sharpness were found between the 2 methods. The XD‐GRASP method provides good‐quality images in the absence of intraphase motion. However, motion blurring is observed in XD‐GRASP images for respiratory phases with larger motion amplitudes and subjects with irregular breathing patterns.ConclusionA robust respiratory‐resolved motion‐compensated framework for Cartesian CMRA has been proposed and tested in healthy subjects and patients. The proposed XD‐ORCCA provides high‐quality images for all respiratory phases, independently of the regularity of the breathing pattern.

OC-0413: 4DCT and VMAT for lung patients with irregular breathing: Phase vs. amplitude binning

OC-0413: 4DCT and VMAT for lung patients with irregular breathing: Phase vs. amplitude binning

PO-0924: 4DCT and VMAT planning for lung patients with irregular breathing

PO-0924: 4DCT and VMAT planning for lung patients with irregular breathing

A Portable Wireless Communication Platform Based on a Multi-Material Fiber Sensor for Real-Time Breath Detection.

In this paper, we present a new mobile wireless communication platform for real-time monitoring of an individual’s breathing rate. The platform takes the form of a wearable stretching T-shirt featuring a sensor and a detection base station. The sensor is formed by a spiral-shaped antenna made from a multi-material fiber connected to a compact transmitter. Based on the resonance frequency of the antenna at approximately 2.4 GHz, the breathing sensor relies on its Bluetooth transmitter. The contactless and non-invasive sensor is designed without compromising the user’s comfort. The sensing mechanism of the system is based on the detection of the signal amplitude transmitted wirelessly by the sensor, which is found to be sensitive to strain. We demonstrate the capability of the platform to detect the breathing rates of four male volunteers who are not in movement. The breathing pattern is obtained through the received signal strength indicator (RSSI) which is filtered and analyzed with home-made algorithms in the portable system. Numerical simulations of human breath are performed to support the experimental detection, and both results are in a good agreement. Slow, fast, regular, irregular, and shallow breathing types are successfully recorded within a frequency interval of 0.16–1.2 Hz, leading to a breathing rate varying from 10 to 72 breaths per minute.

A Noncontact Breathing Disorder Recognition System Using 2.4-GHz Digital-IF Doppler Radar.

In this paper, a noncontact breathing disorder recognition system has been proposed for identifying irregular breathing patterns. The proposed system consists of a Doppler radar-based sensor module and a machine-learning-based breathing disorder recognition module. A custom-designed 2.4-GHz continuous wave digital-IF Doppler radar is utilized as the radar sensor module to accurately capture the time-domain breathing waveform. Then, a recognition module is designed with selected features and optimized classifiers. Four sets of experiments have been carried out to evaluate the proposed system comprehensively. For the laboratorial experiments, the proposed system achieves 94.7% classification accuracy using the linear support vector machine classifier with seven selected features. Results of clinical experiments demonstrate the feasibility of long-term breathing disorder recognition with good accuracy and robustness, and illustrate the potential of the proposed solution for the auxiliary diagnosis of diseases.

Breathe Easy EDA: A MATLAB toolbox for psychophysiology data management, cleaning, and analysis.

Electrodermal activity (EDA) recordings are widely used in experimental psychology to measure skin conductance responses (SCRs) that reflect sympathetic nervous system arousal. However, irregular respiration patterns and deep breaths can cause EDA fluctuations that are difficult to distinguish from genuine arousal-related SCRs, presenting a methodological challenge that increases the likelihood of false positives in SCR analyses. Thus, it is crucial to identify respiration-related artifacts in EDA data. Here we developed a novel and freely distributed MATLAB toolbox, Breathe Easy EDA (BEEDA). BEEDA is a flexible toolbox that facilitates EDA visual inspection, allowing users to identify and eliminate respiration artifacts. BEEDA further includes functionality for EDA data analyses (measuring tonic and phasic EDA components) and reliability analyses for artifact identification. The toolbox is suitable for any experiment recording both EDA and respiration data, and flexibly adjusts to experiment-specific parameters (e.g., trial structure and analysis parameters).

Persistent Expression of Serotonin Receptor 5b Alters Breathing Behavior in Male MeCP2 Knockout Mice

Mutations in the transcription factor methyl-CpG-binding protein 2 (MeCP2) cause the neurodevelopmental disorder Rett syndrome (RTT). Besides many other neurological problems, RTT patients show irregular breathing with recurrent apneas or breath-holdings. MeCP2-deficient mice, which recapitulate this breathing phenotype, show a dysregulated, persistent expression of G-protein-coupled serotonin receptor 5-ht5b (Htr5b) in the brainstem. To investigate whether the persistence of 5-ht5b expression is contributing to the respiratory phenotype, we crossbred MeCP2-deficient mice with 5-ht5b-deficient mice to generate double knockout mice (Mecp2−/y;Htr5b−/−). To compare respiration between wild type (WT), Mecp2−/y and Mecp2−/y;Htr5b−/− mice, we used unrestrained whole-body plethysmography. While the breathing of MeCP2-deficient male mice (Mecp2−/y) at postnatal day 40 is characterized by a slow breathing rate and the occurrence of prolonged respiratory pauses, we found that in MeCP2-deficient mice, which also lacked the 5-ht5b receptor, the breathing rate and the number of pauses were indistinguishable from WT mice. To test for a potential mechanism, we also analyzed if the known coupling of 5-ht5b receptors to Gi proteins is altering second messenger signaling. Tissue cAMP levels in the medulla of Mecp2−/y mice were decreased as compared to WT mice. In contrast, cAMP levels in Mecp2−/y;Htr5b−/− mice were indistinguishable from WT mice. Taken together, our data points towards a role of 5-ht5b receptors within the complex breathing phenotype of MeCP2-deficient mice.

Evaluation of injectable anaesthesia with five medetomidine-midazolam based combinations in Egyptian fruit bats ( Rousettus aegyptiacus).

Egyptian fruit bats are increasingly used as model animals in neuroscience research. Our aim was to characterize suitable injectable anaesthesia for this species, possibly replacing inhalant anaesthesia, thus minimizing occupational health hazards. Eight bats were randomly assigned by a crossover design for subcutaneously administered combinations of medetomidine-midazolam with: saline (MM-Sal), ketamine (MM-Ket), fentanyl (MM-Fen), morphine (MM-Mor), or butorphanol (MM-But). The anaesthetic depth and vital signs were monitored at baseline and every 10 min until bats recovered. If after 180 min the bats did not recover, atipamezole was administered. Mean induction times were 7-11.5 min with all combinations. Twitching during induction was common. All combinations produced anaesthesia, with significantly decreased heart rate (from 400 to 200 bpm) and respiratory rate (from 120-140 to 36-65 rpm). Arrhythmia and irregular breathing patterns occurred. MM-Fen, MM-Mor, and MM-But depressed respiration significantly more than MM-Sal. Time to first movement with MM-Ket and MM-But lasted significantly longer than with MM-Sal. Recovery time was significantly shorter in the MM-Sal (88 min) in comparison to all other treatments, and it was significantly longer in the MM-But (159 min), with atipamezole administered to four of the eight bats. In conclusion, all five anaesthetic protocols are suitable for Egyptian fruit bats; MM-Ket produces long anaesthesia and minimal respiratory depression, but cannot be antagonized completely. MM-Fen, MM-Mor, and MM-But depress respiration, but are known to produce good analgesia, and can be fully antagonized. Administration of atipamezole following the use of MM-But in Egyptian fruit bats is recommended.

REM sleep respiratory behaviours match mental content in narcoleptic lucid dreamers

Breathing is irregular during rapid eye-movement (REM) sleep, whereas it is stable during non-REM sleep. Why this is so remains a mystery. We propose that irregular breathing has a cortical origin and reflects the mental content of dreams, which often accompany REM sleep. We tested 21 patients with narcolepsy who had the exceptional ability to lucid dream in REM sleep, a condition in which one is conscious of dreaming during the dream and can signal lucidity with an ocular code. Sleep and respiration were monitored during multiple naps. Participants were instructed to modify their dream scenario so that it involved vocalizations or an apnoea, -two behaviours that require a cortical control of ventilation when executed during wakefulness. Most participants (86%) were able to signal lucidity in at least one nap. In 50% of the lucid naps, we found a clear congruence between the dream report (e.g., diving under water) and the observed respiratory behaviour (e.g., central apnoea) and, in several cases, a preparatory breath before the respiratory behaviour. This suggests that the cortico-subcortical networks involved in voluntary respiratory movements are preserved during REM sleep and that breathing irregularities during this stage have a cortical/subcortical origin that reflects dream content.

Motion vector field phase-to-amplitude resampling for 4D motion-compensated cone-beam CT

We propose a phase-to-amplitude resampling (PTAR) method to reduce motion blurring in motion-compensated (MoCo) 4D cone-beam CT (CBCT) image reconstruction, without increasing the computational complexity of the motion vector field (MVF) estimation approach. PTAR is able to improve the image quality in reconstructed 4D volumes, including both regular and irregular respiration patterns. The PTAR approach starts with a robust phase-gating procedure for the initial MVF estimation and then switches to a phase-adapted amplitude gating method. The switch implies an MVF-resampling, which makes them amplitude-specific. PTAR ensures that the MVFs, which have been estimated on phase-gated reconstructions, are still valid for all amplitude-gated reconstructions. To validate the method, we use an artificially deformed clinical CT scan with a realistic breathing pattern and several patient data sets acquired with a TrueBeamTM integrated imaging system (Varian Medical Systems, Palo Alto, CA, USA). Motion blurring, which still occurs around the area of the diaphragm or at small vessels above the diaphragm in artifact-specific cyclic motion compensation (acMoCo) images based on phase-gating, is significantly reduced by PTAR. Also, small lung structures appear sharper in the images. This is demonstrated both for simulated and real patient data. A quantification of the sharpness of the diaphragm confirms these findings. PTAR improves the image quality of 4D MoCo reconstructions compared to conventional phase-gated MoCo images, in particular for irregular breathing patterns. Thus, PTAR increases the robustness of MoCo reconstructions for CBCT. Because PTAR does not require any additional steps for the MVF estimation, it is computationally efficient. Our method is not restricted to CBCT but could rather be applied to other image modalities.

Impact of audiovisual biofeedback on interfraction respiratory motion reproducibility in liver cancer stereotactic body radiotherapy.

Irregular breathing motion exacerbates uncertainties throughout a course of radiation therapy. Breathing guidance has demonstrated to improve breathing motion consistency. This was the first clinical implementation of audiovisual biofeedback (AVB) breathing guidance over a course of liver stereotactic body radiotherapy (SBRT) investigating interfraction reproducibility. Five liver cancer patients underwent a screening procedure prior to CT sim during which patients underwent breathing conditions (i) AVB, or (ii) free breathing (FB). Whichever breathing condition was more regular was utilised for the patient's subsequent course of SBRT. Respiratory motion was obtained from the Varian respiratory position monitoring (RPM) system (Varian Medical Systems). Breathing motion reproducibility was assessed by the variance of displacement across 10 phase-based respiratory bins over each patient's course of SBRT. The screening procedure yielded the decision to utilise AVB for three patients and FB for two patients. Over the course of SBRT, AVB significantly improved the relative interfraction motion by 32%, from 22% displacement difference for FB patients to 15% difference for AVB patients. Further to this, AVB facilitated sub-millimetre interfraction reproducibility for two AVB patients. There was significantly less interfraction motion with AVB than FB. These findings demonstrate that AVB is potentially a valuable tool in ensuring reproducible interfraction motion.