The Association of Incidental Radiation Dose to the Heart Base with Overall Survival and Cardiac Events after Curative-intent Radiotherapy for Non-small Cell Lung Cancer: Results from the NI-HEART Study

Overview of cardiac toxicity from radiation therapy

Radiotherapy is an essential part of treatment for many patients with thoracic cancers. However, proximity of the heart to tumour targets can lead to cardiac side effects, with studies demonstrating link between cardiac radiation dose and adverse outcomes. Although reducing cardiac dose can reduce associated risks, most cardiac constraint recommendations in clinical use are generally based on dose to the whole heart, as dose assessment at cardiac substructure levels on individual patients has been limited historically. Furthermore, estimation of an individual's cardiac risk is complex and multifactorial, which includes radiation dose alongside baseline risk factors, and the impact of systemic therapies. This review gives an overview of the epidemiological impact of cancer and cardiac disease, risk factors contributing to radiation-related cardiotoxicity, the evidence for cardiac side effects and future directions in cardiotoxicity research. A better understanding of the interactions between risk factors, balancing treatment benefit versus toxicity and the ongoing management of cardiac risk is essential for optimal clinical care. The emerging field of cardio-oncology is thus a multidisciplinary collaborative effort to enable better understanding of cardiac risks and outcomes for better-informed patient management decisions.

Moving beyond mean heart dose: The importance of cardiac substructures in radiation therapy toxicity

Normal tissue tolerance dose limits to the heart have been established to reduce the risk of radiation-induced cardiac disease (RICD). Dose constraints have been developed based on either the mean dose delivered to the whole heart (MHD) or the dose delivered to a specific volume, for example, volume of heart receiving equal to or greater than 30 Gy (V30). There is increasing evidence that the impact of thoracic radiation on cardiac morbidity and mortality has been underestimated. Consequently, there is a need to reduce the dose delivered to the heart in radical radiotherapy treatment planning. The pathophysiology of RICD may relate to dose to specific cardiac substructures (CS) rather than the traditionally observed MHD for common toxicities. The MHD or V30 Gy threshold dose rarely represents the true dose delivered to individual CS. Studies have shown the dose to specific areas may be more strongly correlated with overall survival (OS). With advances in modern radiotherapy techniques, it is vital that we develop robust, evidence-based dose limits for CS, to fully understand and reduce the risk of RICD, particularly in high-risk populations with cardiac risk factors. The following review will summarise the existing evidence of dose limits to CS, explain how dose limits may vary according to different disease sites or radiation techniques and propose how radiotherapy plans can be optimised to reduce the dose to these CS in clinical practice.

Pilot study to assess the early cardiac safety of carbon ion radiotherapy for intra- and para-cardiac tumours

PURPOSE

Modern photon radiotherapy effectively spares cardiac structures more than previous volumetric approaches. Still, it is related to non-negligible cardiac toxicity due to the low-dose bath of surrounding normal tissues. However, the dosimetric advantages of particle radiotherapy make it a promising treatment for para- and intra-cardiac tumours. In the current short report, we evaluate the cardiac safety profile of carbon ion radiotherapy (CIRT) for radioresistant intra- and para-cardiac malignancies in a real-world setting.

METHODS

We retrospectively analysed serum biomarkers (TnI, CRP and NT-proBNP), echocardiographic, and both 12-lead and 24-hour Holter electrocardiogram (ECG) data of consecutive patients with radioresistant intra- and para-cardiac tumours irradiated with CIRT between June 2019 and September 2022. In the CIRT planning optimization process, to minimize the delivered doses, we contoured and gave a high priority to the cardiac substructures. Weekly re-evaluative 4D computed tomography scans were carried out throughout the treatment.

RESULTS

A total of 16 patients with intra- and para-cardiac localizations of radioresistant tumours were treated up to a total dose of 70.4 Gy relative biological effectiveness (RBE) and a mean heart dose of 2.41 Gy(RBE). We did not record any significant variation of the analysed serum biomarkers after CIRT nor significant changes of echocardiographic features, biventricular strain, or 12-lead and 24-hour Holter ECG parameters during 6 months of follow-up.

CONCLUSION

Our pilot study suggests that carbon ion radiotherapy is a promising radiation technique capable of sparing off-target side effects at the cardiac level. A larger cohort, long-term follow-up and further prospective studies are needed to confirm these findings.

Cardiac Substructure Radiation Dose and Associations With Tachyarrhythmia and Bradyarrhythmia After Lung Cancer Radiotherapy

Background

Arrhythmias are common following radiotherapy for non-small cell lung cancer.

Objectives

The aim of this study was to analyze the association of distinct arrhythmia classes with cardiac substructure radiotherapy dose.

Methods

A retrospective analysis was conducted of 748 patients with locally advanced non-small cell lung cancer treated with radiotherapy. Cardiac substructure dose parameters were calculated. Receiver-operating characteristic curve analyses for predictors of Common Terminology Criteria for Adverse Events grade ≥3 atrial fibrillation (AF), atrial flutter, non-AF and non-atrial flutter supraventricular tachyarrhythmia (SVT), bradyarrhythmia, and ventricular tachyarrhythmia (VT) or asystole were calculated. Fine-Gray regression models were performed (with noncardiac death as a competing risk).

Results

Of 748 patients, 128 (17.1%) experienced at least 1 grade ≥3 arrhythmia, with a median time to first arrhythmia of 2.0 years (Q1-Q3: 0.9-4.2 years). The 2-year cumulative incidences of each arrhythmia group were 8.0% for AF, 2.7% for atrial flutter, 1.8% for other SVT, 1.4% for bradyarrhythmia, and 1.1% for VT or asystole. Adjusting for baseline cardiovascular risk, pulmonary vein (PV) volume receiving 5 Gy was associated with AF (subdistribution HR [sHR]: 1.04/mL; 95% CI: 1.01-1.08; P = 0.016), left circumflex coronary artery volume receiving 35 Gy with atrial flutter (sHR: 1.10/mL; 95% CI: 1.01-1.19; P = 0.028), PV volume receiving 55 Gy with SVT (sHR: 1.03 per 1%; 95% CI: 1.02-1.05; P < 0.001), right coronary artery volume receiving 25 Gy with bradyarrhythmia (sHR: 1.14/mL; 95% CI: 1.00-1.30; P = 0.042), and left main coronary artery volume receiving 5 Gy with VT or asystole (sHR: 2.45/mL; 95% CI: 1.21-4.97; P = 0.013).

Conclusions

This study revealed pathophysiologically distinct arrhythmia classes associated with radiotherapy dose to discrete cardiac substructures, including PV dose with AF and SVT, left circumflex coronary artery dose with atrial flutter, right coronary artery dose with bradyarrhythmia, and left main coronary artery dose with VT or asystole, guiding potential risk mitigation approaches.

Baseline Cardiac Parameters as Biomarkers of Radiation Cardiotoxicity in Lung Cancer: An NI-HEART Analysis

Background

Radiation-induced cardiotoxicity poses a significant challenge in lung cancer management because of the close anatomical proximity of the heart to the lungs, compounded by a high prevalence of cardiovascular risk factors among patients.

Objectives

The aim of this study was to assess the predictive value of routinely available clinical and imaging-based cardiac parameters in identifying "high risk" patients for major adverse cardiac events (MACE) and mortality following radiation therapy (RT).

Methods

The medical records of patients who underwent definitive RT for non-small cell lung cancer using modern planning techniques at a single center between 2015 and 2020 were retrospectively reviewed. Cardiac events were verified by cardiologists, and mortality data were confirmed with the national registry. Cardiac substructures were autosegmented on RT planning scans for retrospective structure and dose analysis, and their correlation with clinical factors was examined. Fine-Gray models were used to analyze relationships while considering the competing risk for death.

Results

Among 478 patients included in the study, 77 (16%) developed 88 MACE, with a median time to event of 16.3 months. A higher burden of pre-existing cardiac diseases was associated with an increased cumulative incidence of MACE (55% [95% CI: 12%-20%] vs 16% [95% CI: 35%-71%]; P < 0.001). Left atrial and left ventricular enlargement on RT planning scans was associated with cumulative incidence of atrial arrhythmia (14% [95% CI: 9%-20%] vs 4% [95% CI: 2%-8%]; P = 0.001) and heart failure (13% [95% CI: 8%-18%] vs 6% [95% CI: 3%-10%]; P = 0.007) at 5 years, respectively. However, myocardial infarction was not associated with the presence of coronary calcium (4.2% [95% CI: 2%-7%] vs 0% [95% CI: 0%-0%]; P = 0.094). No cardiac imaging metrics were found to be both clinically and statistically associated with survival.

Conclusions

The present findings suggest that cardiac history and RT planning scan parameters may offer potential utility in prospectively evaluating cardiotoxicity risk following RT for patients with lung cancer.

A roadmap for modelling radiation-induced cardiac disease

Cardiac risk mitigation is a major priority in improving outcomes for cancer survivors as advances in cancer screening and treatments continue to decrease cancer mortality. More than half of adult cancer patients will be treated with radiotherapy (RT); therefore it is crucial to develop a framework for how to assess and predict radiation-induced cardiac disease (RICD). Historically, RICD was modelled solely using whole heart metrics such as mean heart dose. However, data over the past decade has identified cardiac substructures which outperform whole heart metrics in predicting for significant cardiac events. Additionally, non-RT factors such as pre-existing cardiovascular risk factors and toxicity from other therapies contribute to risk of future cardiac events. In this review, we aim to discuss the current evidence and knowledge gaps in predicting RICD and provide a roadmap for the development of comprehensive models based on three interrelated components, (1) baseline CV risk assessment, (2) cardiac substructure radiation dosimetry linked with cardiac-specific outcomes and (3) novel biomarker development.

A planning study of proton therapy dose escalation for non-small cell lung cancer

In non-small-cell lung cancer (NSCLC), improving local control through radiotherapy dose escalation might improve survival. However, a photon-based RCT showed increased organ at risk dose exposure and worse overall survival in the dose escalation arm. In this study, intensity-modulated proton therapy plans with dose escalation to the primary tumour were created for 20 NSCLC patients. The mediastinal envelope was delineated to spare structures around the heart. It was possible to increase primary tumour dose up to 74.0 Gy without a significant increase in organ at risk doses and predicted toxicity.

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.

Risk of clinically significant cardiovascular disease associated with postoperative radiotherapy in non-small cell lung cancer patients receiving surgical resection followed by adjuvant chemotherapy: A Korean nationwide cohort study

BACKGROUND

There are no large-scale datasets that analyze the relationship between postoperative radiotherapy (PORT) and various cardiovascular diseases (CVDs) in patients with locally advanced non-small cell lung cancer (NSCLC). Therefore, we aimed to investigate the incidences of CVDs with PORT using a national population-based database.

METHODS

Patients diagnosed with NSCLC who underwent curative surgery followed by adjuvant chemotherapy were included from 2007 to 2017. Patients with a prior diagnosis of heart failure (HF), atrial fibrillation (AFib), or heart surgery were excluded. A total of 11,141 patients were included in the final analysis. PORT was used in 1334 patients. Most patients received lobectomy with mediastinal lymph node dissection.

RESULTS

Major adverse cardiac events mostly occurred within 3-4 years from the diagnosis. After the median follow-up duration of 70.6 months, HF was the most diagnosed disease (5.3 %), followed by AFib (4.5 %), stroke (4.1 %), and pulmonary embolism (3.5 %). All the incidences of clinically significant CVDs did not differ by PORT. This result remained unchanged after the propensity score matching comparison. Age ≥ 65, underlying hypertension, and history of ischemic heart disease were the most related factors to the occurrence of HF and AFib. No significant difference in CVD-free survivals according to PORT status was observed. When stratified by proposed scoring, there were no subgroups showed increased incidence by PORT.

CONCLUSIONS

These results suggest that PORT had no significant impact on various CVD occurrences in NSCLC patients without underlying heart disease.

Cardiac substructure delineation in radiation therapy - A state-of-the-art review

Delineation of cardiac substructures is crucial for a better understanding of radiation-related cardiotoxicities and to facilitate accurate and precise cardiac dose calculation for developing and applying risk models. This review examines recent advancements in cardiac substructure delineation in the radiation therapy (RT) context, aiming to provide a comprehensive overview of the current level of knowledge, challenges and future directions in this evolving field. Imaging used for RT planning presents challenges in reliably visualising cardiac anatomy. Although cardiac atlases and contouring guidelines aid in standardisation and reduction of variability, significant uncertainties remain in defining cardiac anatomy. Coupled with the inherent complexity of the heart, this necessitates auto-contouring for consistent large-scale data analysis and improved efficiency in prospective applications. Auto-contouring models, developed primarily for breast and lung cancer RT, have demonstrated performance comparable to manual contouring, marking a significant milestone in the evolution of cardiac delineation practices. Nevertheless, several key concerns require further investigation. There is an unmet need for expanding cardiac auto-contouring models to encompass a broader range of cancer sites. A shift in focus is needed from ensuring accuracy to enhancing the robustness and accessibility of auto-contouring models. Addressing these challenges is paramount for the integration of cardiac substructure delineation and associated risk models into routine clinical practice, thereby improving the safety of RT for future cancer patients.

Pulmonary vein dose and risk of atrial fibrillation in patients with non-small cell lung cancer following definitive radiotherapy: An NI-HEART analysis

BACKGROUND AND PURPOSE

Symptomatic arrhythmia is common following radiotherapy for non-small cell lung cancer (NSCLC), frequently resulting in morbidity and hospitalization. Modern treatment planning technology theoretically allows sparing of cardiac substructures. Atrial fibrillation (AF) comprises the majority of post-radiotherapy arrhythmias, but efforts to prevent this cardiotoxicity have been limited as the causative cardiac substructure is not known. In this study we investigated if incidental radiation dose to the pulmonary veins (PVs) is associated with AF.

MATERIAL AND METHODS

A single-centre study of patients completing contemporary (chemo)radiation for NSCLC, with modern planning techniques. Oncology, cardiology and death records were examined, and AF events were verified by a cardiologist. Cardiac substructures were contoured on planning scans for retrospective dose analysis.

RESULTS

In 420 eligible patients with NSCLC treated with intensity-modulated (70%) or 3D-conformal (30%) radiotherapy with a median OS of 21.8 months (IQR 10.8-35.1), there were 26 cases of new AF (6%). All cases were grade 3 except two cases of grade 4. Dose metrics for both the left (V55) and right (V10) PVs were associated with the incidence of new AF. Metrics remained statistically significant after accounting for the competing risk of death and cardiovascular covariables for both the left (HR 1.02, 95%CI 1.00-1.03, p = 0.005) and right (HR 1.01 (95%CI 1.00-1.02, p = 0.033) PVs.

CONCLUSION

Radiation dose to the PVs during treatment of NSCLC was associated with the onset of AF. Actively sparing the PVs during treatment planning could reduce the incidence of AF during follow-up, and screening for AF may be warranted for select cases.