Dosimetric Impact of Delineation and Motion Uncertainties on the Heart and Substructures in Lung Cancer Radiotherapy

AIMS

Delineation variations and organ motion produce difficult-to-quantify uncertainties in planned radiation doses to targets and organs at risk. Similar to manual contouring, most automatic segmentation tools generate single delineations per structure; however, this does not indicate the range of clinically acceptable delineations. This study develops a method to generate a range of automatic cardiac structure segmentations, incorporating motion and delineation uncertainty, and evaluates the dosimetric impact in lung cancer.

MATERIALS AND METHODS

Eighteen cardiac structures were delineated using a locally developed auto-segmentation tool. It was applied to lung cancer planning CTs for 27 curative (planned dose ≥50 Gy) cases, and delineation variations were estimated by using ten mapping-atlases to provide separate substructure segmentations. Motion-related cardiac segmentation variations were estimated by auto-contouring structures on ten respiratory phases for 9/27 cases that had 4D-planning CTs. Dose volume histograms (DVHs) incorporating these variations were generated for comparison.

RESULTS

Variations in mean doses (Dmean), defined as the range in values across ten feasible auto-segmentations, were calculated for each cardiac substructure. Over the study cohort the median variations for delineation uncertainty and motion were 2.20-11.09 Gy and 0.72-4.06 Gy, respectively. As relative values, variations in Dmean were between 18.7%-65.3% and 7.8%-32.5% for delineation uncertainty and motion, respectively. Doses vary depending on the individual planned dose distribution, not simply on segmentation differences, with larger dose variations to cardiac structures lying within areas of steep dose gradient.

CONCLUSION

Radiotherapy dose uncertainties from delineation variations and respiratory-related heart motion were quantified using a cardiac substructure automatic segmentation tool. This predicts the 'dose range' where doses to structures are most likely to fall, rather than single DVH curves. This enables consideration of these uncertainties in cardiotoxicity research and for future plan optimisation. The tool was designed for cardiac structures, but similar methods are potentially applicable to other OARs.

Management and outcomes with 5-year mortality of patients with mildly elevated high-sensitivity troponin T levels not meeting criteria for myocardial infarction

OBJECTIVES

To examine management and outcomes of patients presenting to EDs with symptoms suggestive of acute coronary syndrome, who have mild non-dynamically elevated high-sensitivity troponin T (HsTnT) levels, not meeting the fourth universal definition of myocardial infarction (MI) criteria (observation group).

METHODS

Consecutive patients presenting to the ED with symptoms suggestive of acute coronary syndrome at Liverpool Hospital, Sydney, Australia, those having ≥2 HsTnT levels after initial assessment were adjudicated according to the fourth universal definition of MI, as MI ruled-in, MI ruled-out, or myocardial injury in whom MI is neither ruled-in nor ruled-out (>1 level ≥15 ng/L, called observation group); follow-up was 5 years.

RESULTS

Of 2738 patients, 547 were in the observation group, of whom 62% were admitted to hospital, 52% to cardiac services, whereas 97% of MI ruled-in patients and 21% of MI ruled-out patients were admitted; P < 0.001. Non-invasive testing occurred in 42% of observation group patients (36% had echo-cardiography), and 16% had coronary angiography. Of observation group patients, MI rates were 1.5% during hospitalisation and 4% during the following year, similar to that in those with MI ruled-in, among those with MI ruled-out, the MI rate was 0.2%. The 1-year death rate was 13% among observation group patients and 11% MI ruled-in patients (P = 0.624), whereas at 5 years among observation group patients, type 1 MI and type 2 MI were 48%, 26% and 58%, respectively (P = 0.001).

CONCLUSION

Very few unselected consecutive patients attending ED, with minor stable HsTnT elevation, had MI, although most had chronic myocardial injury. Late mortality rates among observation group patients were higher than those with confirmed type 1 MI but lower than those with type 2 MI.

Prognostic association supports indexing size measures in echocardiography by body surface area

Body surface area (BSA) is the most commonly used metric for body size indexation of echocardiographic measures, but its use in patients who are underweight or obese is questioned (body mass index (BMI) < 18.5 kg/m2 or ≥ 30 kg/m2, respectively). We aim to use survival analysis to identify an optimal body size indexation metric for echocardiographic measures that would be a better predictor of survival than BSA regardless of BMI. Adult patients with no prior valve replacement were selected from the National Echocardiography Database Australia. Survival analysis was performed for echocardiographic measures both unindexed and indexed to different body size metrics, with 5-year cardiovascular mortality as the primary endpoint. Indexation of echocardiographic measures (left ventricular end-diastolic diameter [n = 230,109] and mass [n = 224,244], left atrial volume [n = 150,540], aortic sinus diameter [n = 90,805], right atrial area [n = 59,516]) by BSA had better prognostic performance vs unindexed measures (underweight: C-statistic 0.655 vs 0.647; normal weight/overweight: average C-statistic 0.666 vs 0.625; obese: C-statistic 0.627 vs 0.613). Indexation by other body size metrics (lean body mass, height, and/or weight raised to different powers) did not improve prognostic performance versus BSA by a clinically relevant magnitude (average C-statistic increase ≤ 0.02), with smaller differences in other BMI subgroups. Indexing measures of cardiac and aortic size by BSA improves prognostic performance regardless of BMI, and no other body size metric has a clinically meaningful better performance.

Decreased diastolic hydraulic forces incrementally associate with survival beyond conventional measures of diastolic dysfunction

Decreased hydraulic forces during diastole contribute to reduced left ventricular (LV) filling and heart failure with preserved ejection fraction. However, their association with diastolic function and patient outcomes are unknown. The aim of this retrospective, cross-sectional study was to determine the mechanistic association between diastolic hydraulic forces, estimated by echocardiography as the atrioventricular area difference (AVAD), and both diastolic function and survival. Patients (n = 5176, median [interquartile range] 5.5 [5.0-6.1] years follow-up, 1213 events) were selected from the National Echo Database Australia (NEDA) based on the presence of relevant transthoracic echocardiographic measures, LV ejection fraction (LVEF) ≥ 50%, heart rate 50-100 beats/minute, the absence of moderate or severe valvular disease, and no prior prosthetic valve surgery. NEDA contains echocardiographic and linked national death index mortality outcome data from 1985 to 2019. AVAD was calculated as the cross-sectional area difference between the LV and left atrium. LV diastolic dysfunction was graded according to 2016 guidelines. AVAD was weakly associated with E/e', left atrial volume index, and LVEF (multivariable global R2 = 0.15, p < 0.001), and not associated with e' and peak tricuspid regurgitation velocity. Decreased AVAD was independently associated with poorer survival, and demonstrated improved model discrimination after adjustment for diastolic function grading (C-statistic [95% confidence interval] 0.644 [0.629-0.660] vs 0.606 [0.592-0.621], p < 0.001) and E/e' (0.649 [0.635-0.664] vs 0.634 [0.618-0.649], p < 0.001), respectively. Therefore, decreased hydraulic forces, estimated by AVAD, are weakly associated with diastolic dysfunction and demonstrate an incremental prognostic association with survival beyond conventional measures used to grade diastolic dysfunction.

Social, Geographical and Income Inequality as Demonstrated by the Coronary Calcium Score: An Ecological Study in Sydney, Australia

BACKGROUND

The coronary calcium score is a non-invasive biomarker of coronary artery disease. The concept of "arterial age" transforms the coronary calcium score to an expected age based on the degree of coronary atherosclerosis. This study aimed to investigate the relationship of socioeconomic status with the burden of coronary artery disease within Sydney, Australia.

METHODS

This was an ecological study at the postcode level of patients aged 45 and above who had completed a CT coronary calcium scan within New South Wales (NSW), Australia from January 2012 to December 2020. Arterial age difference was calculated as arterial age minus chronological age. Socioeconomic data was obtained for median income, Index of Relative Socio-economic Advantage and Disadvantage (IRSAD) score and median property price. Linear regression was used for analysis.

RESULTS

There were 17,102 patients across 325 postcodes within NSW, comprising 9129 males with a median arterial age difference of 7 years and 7972 females with -9 years. Income, IRSAD score and property price each had an inverse relationship with arterial age difference (p-values < 0.05).

CONCLUSIONS

Income, socioeconomic status and local property prices are significantly correlated with premature coronary aging. Healthcare resource allocation and prevention should target the inequalities identified to reduce the burden of coronary artery disease.

Validation of a Fully Automated Hybrid Deep Learning Cardiac Substructure Segmentation Tool for Contouring and Dose Evaluation in Lung Cancer Radiotherapy

BACKGROUND AND PURPOSE

Accurate and consistent delineation of cardiac substructures is challenging. The aim of this work was to validate a novel segmentation tool for automatic delineation of cardiac structures and subsequent dose evaluation, with potential application in clinical settings and large-scale radiation-related cardiotoxicity studies.

MATERIALS AND METHODS

A recently developed hybrid method for automatic segmentation of 18 cardiac structures, combining deep learning, multi-atlas mapping and geometric segmentation of small challenging substructures, was independently validated on 30 lung cancer cases. These included anatomical and imaging variations, such as tumour abutting heart, lung collapse and metal artefacts. Automatic segmentations were compared with manual contours of the 18 structures using quantitative metrics, including Dice similarity coefficient (DSC), mean distance to agreement (MDA) and dose comparisons.

RESULTS

A comparison of manual and automatic contours across all cases showed a median DSC of 0.75-0.93 and a median MDA of 2.09-3.34 mm for whole heart and chambers. The median MDA for great vessels, coronary arteries, cardiac valves, sinoatrial and atrioventricular conduction nodes was 3.01-8.54 mm. For the 27 cases treated with curative intent (planned target volume dose ≥50 Gy), the median dose difference was -1.12 to 0.57 Gy (absolute difference of 1.13-3.25%) for the mean dose to heart and chambers; and -2.25 to 4.45 Gy (absolute difference of 0.94-6.79%) for the mean dose to substructures.

CONCLUSION

The novel hybrid automatic segmentation tool reported high accuracy and consistency over a validation set with challenging anatomical and imaging variations. This has promising applications in substructure dose calculations of large-scale datasets and for future studies on long-term cardiac toxicity.

Open-source, fully-automated hybrid cardiac substructure segmentation: development and optimisation

Radiotherapy for thoracic and breast tumours is associated with a range of cardiotoxicities. Emerging evidence suggests cardiac substructure doses may be more predictive of specific outcomes, however, quantitative data necessary to develop clinical planning constraints is lacking. Retrospective analysis of patient data is required, which relies on accurate segmentation of cardiac substructures. In this study, a novel model was designed to deliver reliable, accurate, and anatomically consistent segmentation of 18 cardiac substructures on computed tomography (CT) scans. Thirty manually contoured CT scans were included. The proposed multi-stage method leverages deep learning (DL), multi-atlas mapping, and geometric modelling to automatically segment the whole heart, cardiac chambers, great vessels, heart valves, coronary arteries, and conduction nodes. Segmentation performance was evaluated using the Dice similarity coefficient (DSC), mean distance to agreement (MDA), Hausdorff distance (HD), and volume ratio. Performance was reliable, with no errors observed and acceptable variation in accuracy between cases, including in challenging cases with imaging artefacts and atypical patient anatomy. The median DSC range was 0.81-0.93 for whole heart and cardiac chambers, 0.43-0.76 for great vessels and conduction nodes, and 0.22-0.53 for heart valves. For all structures the median MDA was below 6 mm, median HD ranged 7.7-19.7 mm, and median volume ratio was close to one (0.95-1.49) for all structures except the left main coronary artery (2.07). The fully automatic algorithm takes between 9 and 23 min per case. The proposed fully-automatic method accurately delineates cardiac substructures on radiotherapy planning CT scans. Robust and anatomically consistent segmentations, particularly for smaller structures, represents a major advantage of the proposed segmentation approach. The open-source software will facilitate more precise evaluation of cardiac doses and risks from available clinical datasets.

Fluid structure computational model of simulating mitral valve motion in a contracting left ventricle

BACKGROUND

Fluid structure interaction simulations h hold promise in studying normal and abnormal cardiac function, including the effect of fluid dynamics on mitral valve (MV) leaflet motion. The goal of this study was to develop a 3D fluid structure interaction computational model to simulate bileaflet MV when interacting with blood motion in left ventricle (LV).

METHODS

The model consists of ideal geometric-shaped MV leaflets and the LV, with MV dimensions based on human anatomical measurements. An experimentally-based hyperelastic isotropic material was used to model the mechanical behaviour of the MV leaflets, with chordae tendineae and papillary muscle tips also incorporated. LV myocardial tissue was prescribed using a transverse isotropic hyperelastic formulation. Incompressible Navier-Stokes fluid formulations were used to govern the blood motion, and the Arbitrary Lagrangian Eulerian (ALE) method was employed to determine the mesh deformation of the fluid and solid domains due to trans-valvular pressure on MV boundaries and the resulting leaflet movement.

RESULTS

The LV-MV generic model was able to reproduce physiological MV leaflet opening and closing profiles resulting from the time-varying atrial and ventricular pressures, as well as simulating normal and prolapsed MV states. Additionally, the model was able to simulate blood flow patterns after insertion of a prosthetic MV with and without left ventricular outflow tract flow obstruction. In the MV-LV normal model, the regurgitant blood flow fraction was 10.1 %, with no abnormality in cardiac function according to the mitral regurgitation severity grades reported by the American Society of Echocardiography.

CONCLUSION

Our simulation approach provides insights into intraventricular fluid dynamics in a contracting LV with normal and prolapsed MV function, as well as aiding in the understanding of possible complications after transcatheter MV implantation prior to clinical trials.

Role of cardiac magnetic resonance imaging in troponinemia syndromes

Cardiac magnetic resonance imaging (MRI) is an evolving technology, proving to be a highly accurate tool for quantitative assessment. Most recently, it has been increasingly used in the diagnostic and prognostic evaluation of conditions involving an elevation in troponin or troponinemia. Although an elevation in troponin is a nonspecific marker of myocardial tissue damage, it is a frequently ordered investigation leaving many patients without a specific diagnosis. Fortunately, the advent of newer cardiac MRI protocols can provide additional information. In this review, we discuss several conditions associated with an elevation in troponin such as myocardial infarction, myocarditis, Takotsubo cardiomyopathy, coronavirus disease 2019 related cardiac dysfunction and athlete’s heart syndrome.

Machine learning analysis of chest CT to detect cardiac abnormalities in COVID19

Introduction

Standard, un-gated chest CT can be used as the basis of detailed segmentation of the atrial and ventricular cardiac chambers. In conditions such as COVID19 where dedicated cardiac imaging may be hazardous or unavailable atlas-based machine learning tools allow automatic quantification of cardiac morphology and may allow early detection of abnormalities.

Purpose

To develop an automated screening tool to detect cardiac changes associated with COVID19 on chest/lung CT to allow early treatment and appropriate selection of patients for dedicated cardiac imaging.

Methods

A previously validated atlas-based cardiac contouring algorithm was modified to work within the setting of variable and severe lung pathology. The modified technique was used to segment the left and right atria and ventricles from non-contrast CT scans. We applied the developed algorithm to the Moscow University COVID19 CT dataset. 1110 scans were available. COVID19 severity was graded 0 to 4. Grade 4 was not used in analysis due to insufficient numbers. Cardiac chamber sizes were compared according to COVID19 severity status. In a limited cohort of repeat studies, the feasibility of polar mapping to demonstrated serial morphological change was tested.

Results

A statistically significant increase of average cardiac chamber volumes was noted relative to mild Grade 0 COVID19 at every incremental severity grade (Figure 1). Changes in average ventricular volumes were greater (up to 15.2% and 16.9% for left and right ventricles) than changes in atrial volumes (up 12.1% and 7.6% for left and right atria). Automated quantification was successful in the large majority of cases and inter-patient polar mapping of sequential data to detect progressive chamber enlargement appears feasible (Figure 2).

Conclusion

Machine learning methods permit automatic quantification of cardiac chamber size from standard lung CT scans. Cardiac changes on lung CT examinations may be used to identify cardiac abnormalities at an early stage and could be useful to triage individuals for dedicated cardiac investigations. With further refinement, this method may be useful to detect and track temporal cardiac changes in COVID19, as well as in other pulmonary pathology and conditions in which chest CT is routinely used.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): SPHERE Research consortium Figure 1Figure 2

3D Printing for Cardiovascular Applications: From End-to-End Processes to Emerging Developments

3D printing as a means of fabrication has seen increasing applications in medicine in the last decade, becoming invaluable for cardiovascular applications. This rapidly developing technology has had a significant impact on cardiovascular research, its clinical translation and education. It has expanded our understanding of the cardiovascular system resulting in better devices, tools and consequently improved patient outcomes. This review discusses the latest developments and future directions of generating medical replicas ('phantoms') for use in the cardiovascular field, detailing the end-to-end process from medical imaging to capture structures of interest, to production and use of 3D printed models. We provide comparisons of available imaging modalities and overview of segmentation and post-processing techniques to process images for printing, detailed exploration of latest 3D printing methods and materials, and a comprehensive, up-to-date review of milestone applications and their impact within the cardiovascular domain across research, clinical use and education. We then provide an in-depth exploration of future technologies and innovations around these methods, capturing opportunities and emerging directions across increasingly realistic representations, bioprinting and tissue engineering, and complementary virtual and mixed reality solutions. The next generation of 3D printing techniques allow patient-specific models that are increasingly realistic, replicating properties, anatomy and function.

Cardiac magnetic resonance derived left atrial strain after ST-elevation myocardial infarction: an independent prognostic indicator

Background

The prognostic value of cardiac magnetic resonance (CMR) derived left atrial (LA) strain, ejection fraction (LAEF) and indexed volumes (LAVI_max and LAVI_min) after ST-elevation myocardial infarction (STEMI) remains controversial. The aim of this study was to assess the relationship between LA function and major adverse cardiovascular events (MACE) after STEMI.

Methods

A total of 202 prospectively recruited patients who underwent CMR at median day 4 after STEMI had complete CMR data for feature tracking assessment. LA reservoir and booster strain were quantified based on the average of three independently repeated measurements.

Results

MACE occurred in 35 patients during a median follow up of 607 days. Patients with MACE had lower median LA reservoir strain (18.9% vs. 29.4%, P<0.001), LA booster strain (9.4% vs. 13.0%, P=0.002) and LAEF (41.5% vs. 49.2%, P<0.001) than patients without MACE. Kaplan-Meier analyses demonstrated a difference in MACE between high- and low-risk groups for LA reservoir strain (cutoff 19.2%, P<0.001), LA booster strain (cutoff 9.7%, P<0.001) and LAEF (cutoff 38.5%, P<0.001). The AUC increased from 0.713 (95% CI: 0.608-0.818) for LVEF to 0.775 (95% CI: 0.680-0.870) when LA reservoir strain was added to LVEF (P=0.047). Univariate Cox regression analysis showed that all LA parameters had a significant effect on MACE, while multivariate analysis found LA reservoir strain was an independent predictor of MACE (HR 0.905; 95% CI: 0.843-0.972, P=0.006).

Conclusions

CMR derived LA reservoir strain independently predicted MACE after STEMI when adjusted for standard risk measures.

Segmental Cardiac Radiation Dose Determines Magnitude of Regional Cardiac Dysfunction

Background

Subclinical left ventricular dysfunction detected by 2‐dimensional global longitudinal strain post breast radiotherapy has been described in patients with breast cancer. We hypothesized that left ventricular dysfunction postradiotherapy may be site specific, based on differential segmental radiotherapy dose received.

Methods and Results

Transthoracic echocardiograms were performed at baseline, 6 weeks, and 12 months postradiotherapy on 61 chemotherapy‐naïve women with left‐sided breast cancer undergoing tangential breast radiotherapy. Radiation received within basal, mid, and apical regions for the 6 left ventricular walls was quantified from the radiotherapy treatment planning system. Anterior, anteroseptal, and anterolateral walls received the highest radiation doses, while inferolateral and inferior walls received the lowest. There was a progressive increase in the radiation dose received from basal to apical regions. At 6 weeks, the most significant percentage deterioration in strain was seen in the apical region, with greatest reductions in the anterior wall followed by the anteroseptal and anterolateral walls, with a similar pattern persisting at 12 months. There was a within‐patient dose–response association between the segment‐specific percentage deterioration in strain at 6 weeks and 12 months and the radiation dose received.

Conclusions

Radiotherapy for left‐sided breast cancer causes differential segmental dysfunction, with myocardial segments that receive the highest radiation dose demonstrating greatest strain impairment. Percentage deterioration in strain observed 6 weeks postradiotherapy persisted at 12 months and demonstrated a dose–response relationship with radiotherapy dose received. Radiotherapy‐induced subclinical cardiac dysfunction is of importance because it could be additive to chemotherapy‐related cardiotoxicity in patients with breast cancer. Long‐term outcomes in patients with asymptomatic strain reduction require further investigation.

Direct comparison of multilayer left ventricular global longitudinal strain using CMR feature tracking and speckle tracking echocardiography

Background

Cardiac magnetic resonance feature tracking (CMR-FT) and speckle tracking echocardiography (STE) are well-established strain imaging modalities. Multilayer strain measurement permits independent assessment of endocardial and epicardial strain. This novel and layer specific approach to evaluating myocardial deformation parameters may provide greater insight into cardiac contractility when compared to whole-layer strain analysis. The aim of this study is to validate CMR-FT as a tool for multilayer strain analysis by providing a direct comparison between multilayer global longitudinal strain (GLS) values between CMR-FT and STE.

Methods

We studied 100 patients who had an acute myocardial infarction (AMI), who underwent CMR imaging and echocardiogram at baseline and follow-up (48 ± 13 days). Dedicated tissue tracking software was used to analyse single- and multi-layer GLS values for CMR-FT and STE.

Results

Correlation coefficients for CMR-FT and STE were 0.685, 0.687, and 0.660 for endocardial, epicardial, and whole-layer GLS respectively (all p < 0.001). Bland Altman analysis showed good inter-modality agreement with minimal bias. The absolute limits of agreement in our study were 6.4, 5.9, and 5.5 for endocardial, whole-layer, and epicardial GLS respectively. Absolute biases were 1.79, 0.80, and 0.98 respectively. Intraclass correlation coefficient (ICC) values showed moderate agreement with values of 0.626, 0.632, and 0.671 respectively (all p < 0.001).

Conclusion

There is good inter-modality agreement between CMR-FT and STE for whole-layer, endocardial, and epicardial GLS, and although values should not be used interchangeably our study demonstrates that CMR-FT is a viable imaging modality for multilayer strain

Regional cardiac dysfunction determined by radiation dose in patients with breast cancer

Background

Subclinical left ventricular (LV) dysfunction by 2D global longitudinal strain (GLS) immediately following radiotherapy (RT) and persisting at 12 months has been described in breast cancer (BC) patients. We hypothesised that persistent LV dysfunction may be regional and correlate with segmental RT.

Methods

Transthoracic echocardiograms were performed at baseline, 6 weeks and 12 months post-RT on 61 chemotherapy-naïve women with left sided BC.

Results

Anterior and anteroseptal regions received the highest radiation dose, and posterior and inferior segments the lowest radiation dose (Figure 1). Within each region, there was a progressive increase in the radiation dose received from base to apex. At 6 weeks, the greatest reduction in strain was observed in the anterior and anteroseptal regions, with the most significant reduction in strain in the apical segments. At 12 months, despite improvement in strain, the percentage reduction in strain was similar. There was a significant interaction between both region and segment, on the percentage change in strain at 6 weeks (p&lt;0.001) and at 12 months (p=0.007). Pairwise comparisons of apical to basal percentage change in strain demonstrated the most significant reductions in the anterior region at 6 weeks and 12 months (Table 1).

Conclusions

RT causes segmental myocardial dysfunction, with areas receiving the highest RT demonstrating the largest impairment in strain, with these changes persisting at 12 months. Long term correlation with adverse events is required.

Figure 1. Radiation dose by region and segment

Funding Acknowledgement

Type of funding source: None

Cardiac magnetic resonance derived left atrial function after ST-elevation myocardial infarction: an important prognostic indicator

Background

The prognostic value of cardiac magnetic resonance (CMR) derived left atrial (LA) strain, ejection fraction (LAEF) and volumes (LAVImax and LAVImin) after STEMI is controversial.

Aim

To assess the relationship between LA function and major adverse cardiovascular events (MACE) within 2 years after STEMI.

Methods

We prospectively recruited 213 consecutive STEMI patients who underwent CMR at median day 4. 202 patients had complete CMR data for feature tracking assessment. LA reservoir and booster strain were quantified by one blinded observer based on the average of three independently repeated measurements from two- and four-chamber views. MACE was a composite of all-cause mortality, reinfarction, new or worsening heart failure, stroke and sustained ventricular arrhythmias.

Results

The cohort included 174 (86.1%) males, median age 56 years (IQR 50–65 years). MACE occurred in 35 (17.3%) patients. Patients with MACE had lower median reservoir strain (18.9 vs 29.4%, p&lt;0.001), booster strain (9.4 vs 13.0%, p=0.002) and LAEF (41.5 vs 49.2%, p&lt;0.001), and higher LAVImax (43.5 vs 38.6ml/m2, p=0.019) and LAVImin (23.7 vs 19.3ml/m2, p&lt;0.001) than patients without MACE. Patients with reduced left ventricular ejection fraction (LVEF≤40%) had lower median reservoir strain (22.5 vs 30.1%, p&lt;0.001), booster strain (11.3 vs 12.9%, p=0.021) and LAEF (43.3 vs 50.3%, p&lt;0.001) than patients with LVEF&gt;40%. AUC analyses showed reservoir strain (AUC 0.769; 95% CI 0.676–0.861, p&lt;0.001), booster strain (AUC 0.684; 95% CI 0.558–0.810, p=0.002) and LAEF (AUC 0.698; 95% CI 0.596–0.800, p&lt;0.001) predicted MACE. Kaplan Meier analyses showed a difference in MACE between high- and low-risk groups for reservoir strain (cutoff 21%, p&lt;0.001), booster strain (cutoff 9.6%, p&lt;0.001) and LAEF (cutoff 41%, p&lt;0.001). Univariate Cox regression analyses showed all LA parameters had a significant effect on MACE, while multivariate analyses found additional prognostic utility using reservoir strain.

Conclusion

LA reservoir strain provided incremental prognostic value beyond established clinical and CMR parameters for predicting MACE after STEMI.

Kaplan Meier analyses

Funding Acknowledgement

Type of funding source: None

Intra- and inter-observer reproducibility of multilayer cardiac magnetic resonance feature tracking derived longitudinal and circumferential strain

Background

Multilayer strain measurement with cardiac magnetic resonance feature tracking (CMR-FT) allows independent assessment of endocardial and epicardial strain. This novel method of layer-specific quantification of myocardial deformation parameters provides greater insight into contractility compared to whole-layer strain analysis. The clinical utility of this technique is promising. The aim of this study is to investigate the intra- and inter- observer reproducibility of CMR-FT derived multilayer global longitudinal strain (GLS) and global circumferential strain (GCS) parameters in the setting of normal cardiac function, cardiac pathology, and differing MRI field strengths.

Methods

We studied 4 groups of 20 subjects, comprising of patients with dilated cardiomyopathy, ischemic heart disease, and patients without cardiac pathology at both 1.5 and 3 T. Quantitative measures of whole-layer and multi-layer longitudinal and circumferential strain were calculated using CMR-FT software.

Results

Intraclass correlation coefficients (ICC) for intraobserver reproducibility of endocardial, epicardial, and whole-layer measurements of GLS were 0.979, 0.980, and 0.978 respectively, and those for GCS were 0.986, 0.977, and 0.985. ICCs for inter-observer reproducibility of endocardial, epicardial, and whole-layer measurements of GLS were 0.976, 0.970, and 0.976, and those for GCS were 0.982, 0.969, and 0.981. Bland Altman analysis showed minimal bias and acceptable limits of agreement (LOA) within each patient subgroup and the overall cohort. Circumferential and longitudinal strain parameters were equally reproducible in the overall cohort.

Conclusions

CMR-FT derived multilayer measurements of longitudinal and circumferential strain demonstrate high intra- and inter- observer reproducibility, with suitability for use in clinical practice.

Reduction in radiation exposure in cardiovascular computed tomography imaging: results from the PROspective multicenter registry on radiaTion dose Estimates of cardiac CT angIOgraphy iN daily practice in 2017 (PROTECTION VI)

Aims

Advances of cardiac computed tomography angiography (CTA) have been developed for dose reduction, but their efficacy in clinical practice is largely unknown. This study was designed to evaluate radiation dose exposure and utilization of dose-saving strategies for contrast-enhanced cardiac CTA in daily practice.

Methods and results

Sixty one hospitals from 32 countries prospectively enrolled 4502 patients undergoing cardiac CTA during one calendar month in 2017. Computed tomography angiography scan data and images were analysed in a central core lab and compared with a similar dose survey performed in 2007. Linear regression analysis was performed to identify independent predictors associated with dose. The most frequent indication for cardiac CTA was the evaluation of coronary artery disease in 89% of patients. The median dose-length product (DLP) of coronary CTA was 195 mGy*cm (interquartile range 110-338 mGy*cm). When compared with 2007, the DLP was reduced by 78% (P < 0.001) without an increase in non-diagnostic coronary CTAs (1.7% in 2007 vs. 1.9% in 2017 surveys, P = 0.55). A 37-fold variability in median DLP was observed between the hospitals with lowest and highest DLP (range of median DLP 57-2090 mGy*cm). Independent predictors for radiation dose of coronary CTA were: body weight, heart rate, sinus rhythm, tube voltage, iterative image reconstruction, and the selection of scan protocols.

Conclusion

This large international radiation dose survey demonstrates considerable reduction of radiation exposure in coronary CTA during the last decade. However, the large inter-site variability in radiation exposure underlines the need for further site-specific training and adaptation of contemporary cardiac scan protocols.

4938Left ventricular global longitudinal strain recovery predicts scar size reduction and systolic remodelling post ST-elevation myocardial infarction

Background

Left ventricular (LV) strain has prognostic utility following ST-elevation myocardial infarction (STEMI); however, serial changes in LV strain has not been evaluated post-infarct. We sought to determine the relationship between post-STEMI transthoracic echocardiographic (TTE) LV global longitudinal strain (GLS) and cardiac magnetic resonance (CMR) imaging derived scar size and LV systolic remodelling.

Methods

Following revascularisation, 172 first STEMI patients (85% male, 56.9±10.7 years) had paired TTE for GLS, and CMR to evaluate scar size and LV systolic function at baseline (2–7 days) and follow-up (8–10 weeks). Patients were divided into 3 groups according to absolute baseline GLS: group 1 (GLS ≥16%), group 2 (12%< GLS <16%), group 3 (GLS ≤12%). GLS recovery was defined as ≥10% increase in GLS at follow-up, excluding patients with normal baseline GLS. LV systolic adverse remodelling was defined as ≥15% increase in LVESV. LV systolic reverse remodelling was defined as ≥15% decrease in LVESV. Scar reduction was defined as ≥30% decrease in scar size.

Results

Group 1 and 2 had smaller follow-up scar size and higher LVEF compared to group 3 (p<0.0001 for both, see table). There was no difference in scar size reduction or systolic reverse remodeling among the baseline GLS groups (p>0.05 for both). Importantly, no patients from group 1 demonstrated systolic adverse remodelling. Relative change in GLS is significantly correlated with changes in LVEF (r=0.354, p<0.0001) and scar size (r=−0.262, p<0.0001), see figure. On multivariate binary logistic analysis, patients who demonstrated GLS recovery had greater reduction in scar size (OR=2.77 (1.09–7.01), p=0.032) and LV systolic reverse remodelling (OR=9.63 (1.21–76.41), p=0.032).

Follow-up parameters within GLS groups All patients (n=172) Group 1 (n=47) Group 2 (n=72) Group 3 (n=53) Follow-up GLS, % 16.02±3.44 19.38±1.90 16.36±2.09 12.57±2.69 GLS recovery, n 110 (64%) 19 (40%) 53 (74%) 38 (72%) Follow-up scar size, % 7.67±5.40 5.01±3.38 6.27±3.73 12.02±6.24 Follow-up LVEF, % 51.80±10.20 57.83±6.95 54.14±8.02 43.26±9.83 Data presented as mean ± SD or n (%).

Correlation graphs for change in GLS

Conclusion

Stratification of STEMI patients by baseline GLS was a determinant of CMR scar size as well as LV systolic function. However, the evaluation of GLS recovery could provide additional insights into reduction in scar size and LV systolic remodelling, both important prognostic markers. Thus, echocardiographic serial GLS evaluation may be a relevant non-invasive parameter, that is cheaper and more widely available for monitoring STEMI patients and guiding therapy.

P1483Serial changes in peak left atrial strain predicts diastolic remodelling following percutaneous revascularisation for ST-segment elevation myocardial infarction

Background

Echocardiographic 2D speckle tracking peak left atrial (LA) strain reflects LA reservoir function. Limited studies have reported the relationship between peak LA strain and diastolic dysfunction. In addition, adverse diastolic remodeling (ADR) has been reported, to have better prognostic value than single diastolic function assessment following ST-elevation myocardial infarction (STEMI).

Purpose

We examined the relationship between serial changes in echocardiographic peak LA strain and diastolic function in STEMI patients.

Methods

186 percutaneously revascularized first presentation STEMI patients (87% male, 56.9±10.6 years) underwent serial TTE at baseline (2–7 days) and at follow-up (8–10 weeks) post-STEMI. Peak LA reservoir strain measurements were analysed from apical 2-, 3- and 4- chamber views. Diastolic function was graded as per 2016 guidelines: normal, grade 1, grade 2 and grade 3. ADR was defined as worsening of diastolic function grade (≥1) from baseline to follow-up, or persistent grade 3.

Results

Lower baseline peak LA strain was associated with grade 2 and grade 3 diastolic dysfunction compared to normal and grade 1 function at follow-up (p<0.05, see figure and table). Change in LA strain was less with worsening grades of diastolic function (see table). ADR was seen in 33 patients. Lower baseline peak LA strain predicted ADR (B=0.86 (0.80–0.92), p<0.0001). In addition, a reduction in peak LA strain at follow up was independently associated with ADR (B=0.91 (0.84–0.97), p=0.007) (see figure).

Diastolic function grades with LA strain Follow-up diastolic function Baseline peak LA strain (%) Follow-up peak LA strain (%) Change in peak LA strain (%) Normal (n=91) 35.70±6.38 40.97±8.10 5.26±6.07 Grade 1 (n=61) 30.70±6.97 34.54±8.77 3.84±6.32 Grade 2 (n=17) 23.95±6.11 25.49±5.93 1.54±4.70 Grade 3 (n=17) 23.66±8.07 23.49±10.64 −0.17±7.44 Data presented as mean ± SD.

Peak LA strain vs diastolic function

Conclusion

Peak LA strain is associated with diastolic function following STEMI and differentiates normal diastolic function from diastolic dysfunction. Serial changes in peak LA strain correlated with diastolic remodelling. Longer-term follow-up is required to determine the prognostic value of changes in peak LA strain, and diastolic remodelling.

Feasibility of multi-atlas cardiac segmentation from thoracic planning CT in a probabilistic framework

Toxicity to cardiac and coronary structures is an important late morbidity for patients undergoing left-sided breast radiotherapy. Many current studies have relied on estimates of cardiac doses assuming standardised anatomy, with a calculated increase in relative risk of 7.4% per Gy (mean heart dose). To provide individualised estimates for dose, delineation of various cardiac structures on patient images is required. Automatic multi-atlas based segmentation can provide a consistent, robust solution, however there are challenges to this method. We are aiming to develop and validate a cardiac atlas and segmentation framework, with a focus on the limitations and uncertainties in the process. We present a probabilistic approach to segmentation, which provides a simple method to incorporate inter-observer variation, as well as a useful tool for evaluating the accuracy and sources of error in segmentation. A dataset consisting of 20 planning computed tomography (CT) images of Australian breast cancer patients with delineations of 17 structures (including whole heart, four chambers, coronary arteries and valves) was manually contoured by three independent observers, following a protocol based on a published reference atlas, with verification by a cardiologist. To develop and validate the segmentation framework a leave-one-out cross-validation strategy was implemented. Performance of the automatic segmentations was evaluated relative to inter-observer variability in manually-derived contours; measures of volume and surface accuracy (Dice similarity coefficient (DSC) and mean absolute surface distance (MASD), respectively) were used to compare automatic segmentation to the consensus segmentation from manual contours. For the whole heart, the resulting segmentation achieved a DSC of [Formula: see text], with a MASD of [Formula: see text] mm. Quantitative results, together with the analysis of probabilistic labelling, indicate the feasibility of accurate and consistent segmentation of larger structures, whereas this is not the case for many smaller structures, where a major limitation in segmentation accuracy is the inter-observer variability in manual contouring.

Quantification of cardiac subvolume dosimetry using a 17 segment model of the left ventricle in breast cancer patients receiving tangential beam radiotherapy

PURPOSE

Subacute changes following breast radiotherapy have been demonstrated in discrete areas of the left ventricle (LV), with recent guidelines being developed to help determine dose to subvolumes of the LV. This study aims to determine doses to the 17 segments of the LV as per the American Heart Association (AHA) and other cardiac subvolumes, and to correlate mean heart (MHD) dose with various subvolume dosimetric indices. These results may direct focus to specific left ventricular segments in studies of radiation-related heart disease incorporating surveillance imaging, help to determine more precise dose response relationships, and potentially aid prediction of late radiation effects.

METHODS AND MATERIALS

The heart and cardiac subvolumes of 29 patients treated with tangential radiotherapy for left breast cancer were contoured. Delineation of cardiac subvolumes (cardiac chambers, cardiac valves and the 17 segments of the LV) was undertaken using a novel contouring method on planning CT data reformatted into the cardiac axis. Individual segments were then combined to determine doses to the basal, mid and apical left ventricular regions, and the anterior, septal, inferior and lateral ventricular walls. Radiotherapy doses (including maximum, mean, D1cc, V25) were determined. Correlation analyses were performed between MHD and various substructure dosimetric indices.

RESULTS

Twenty five patients received tangential breast free breathing radiotherapy alone, and four patients received regional nodal irradiation including the internal mammary chain with deep inspiration breath hold (DIBH). For patients receiving breast only radiation, the median mean heart radiation dose was 2.62 Gy (range 1.52-3.90 Gy), and a heterogeneous dose distribution to the LV was noted, with the apical region receiving the highest median mean dose (14.99 Gy) compared with the mid and basal regions (3.10 Gy and 1.51 Gy respectively). The anterior LV wall received the highest median mean dose (9.21 Gy) with the remaining walls receiving similar mean doses (range 1.79-3.05 Gy). The anterior LV apical segment (segment 13) and apex (segment 17) received the highest individual median mean segment doses (26.73 Gy and 30.02 Gy respectively). Apical segments received the highest median mean doses (segments 13, 14, 15, 16), followed by the mid anterior (segment 7) and anteroseptal (segment 8) segments. Segments receiving the highest doses remained unchanged between the DIBH cohort and free breathing cohort. MHD showed a high correlation with the anterior wall r = 0.71, p < 0.05 and entire left ventricle r = 0.82, p < 0.05, but correlations varied from weak to high when MHD was correlated with segments receiving highest doses (range r = 0.43-0.76), p < 0.05.

CONCLUSIONS

In the setting of breast cancer radiotherapy, there are substantial RT dose variations within specific LV segments, with mid and apical anterior ventricular segments (segments 7, 13) and the apical region of the LV (segments 13, 14, 15, 16, 17) being consistently exposed to the highest radiation doses. Determining segmental and regional RT doses to the left ventricle may help guide focus in diagnostic cardiology in the post radiotherapy setting.