Cardiac-sparing radiotherapy for locally advanced non-small cell lung cancer

Cardiotoxicity following thoracic radiotherapy for lung cancer

Radiotherapy is the standard of care treatment for unresectable NSCLC, combined with concurrent chemotherapy and adjuvant immunotherapy. Despite technological advances in radiotherapy planning and delivery, the risk of damage to surrounding thoracic tissues remains high. Cardiac problems, including arrhythmia, heart failure and ischaemic events, occur in 20% of patients with lung cancer who undergo radiotherapy. As survival rates improve incrementally for this cohort, minimising the cardiovascular morbidity of RT is increasingly important. Problematically, the reporting of cardiac endpoints has been poor in thoracic radiotherapy clinical trials, and retrospective studies have been limited by the lack of standardisation of nomenclature and endpoints. How baseline cardiovascular profile and cardiac substructure radiation dose distribution impact the risk of cardiotoxicity is incompletely understood. As Thoracic Oncology departments seek to expand the indications for radiotherapy, and as the patient cohort becomes older and more comorbid, there is a pressing need for cardiotoxicity to be comprehensively characterised with sophisticated oncology, physics and cardio-oncology evaluations. This review synthesises the evidence base for cardiotoxicity in conventional radiotherapy, focusing on lung cancer, including current data, unmet clinical needs, and future scientific directions.

Parallel explorations in LA-NSCLC: Chemoradiation dose-response optimisation considering immunotherapy and cardiac toxicity sparing

BACKGROUND AND PURPOSE

Chemoradiotherapy (CRT) for locally-advanced non-small cell lung cancer (LA-NSCLC) has undergone advances, including increased overall survival (OS) when combined with immune checkpoint blockade (ICB), and using cardiac-sparing techniques to reduce the radiotoxicity. This research investigated 1) how radiotherapy schedules can be optimised with CRT-ICB schemes, and 2) how cardiac-sparing might change the OS for concurrent CRT (cCRT).

METHODS AND MATERIALS

Survival data and dosimetric indices were sourced from published studies, with 2-year OS standardised and the hazard ratio of mean heart dose (MHD) against radiotoxicity tabulated in purpose. A published CRT dose-response model was selected, then modified with ICB and cardiac-sparing hypotheses. Models were maximum likelihood fitted, then visualised the prediction outcomes after bootstrapping.

RESULTS

The modelled 2-year OS rate of cCRT-ICB reached 71 % (95 % confidence intervals, CI 62 %, 84 %) and 66 % (95 % CI: 53 %, 81 %) for stage IIIA and IIIB/C, respectively, given 60 Gy in 2 Gy-per-fraction. 60 Gy in 30 fractions remained the best schedule for cCRT-ICB, whereas modest dose de-escalation to 55 Gy only reduced the OS in 2 %. Sequential CRT (sCRT)-ICB provided 6 % OS increases versus the best OS rate achieved by sCRT alone. Photon MHD-sparing achieved a 5-10 % increase in modelled 2-year OS, with protons providing a further roughly 5-10 % increase.

CONCLUSION

Neither dose-escalation nor de-escalation relative to 60 Gy in 30 fractions influenced the survival with cCRT-ICB, while 5 Gy dose de-escalation might benefit patients with heavily irradiated organs at risk. Cardiac-sparing improved OS, and protons provided advantages for tumours anatomically overlapped or lay below the heart.

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.

Factors associated with acute esophagitis during radiation therapy for lung cancer

INTRODUCTION

Limiting acute esophagitis remains a clinical challenge during the treatment of locally advanced non-small cell lung cancer (NSCLC).

METHODS

Demographic, dosimetric, and acute toxicity data were prospectively collected for patients undergoing definitive radiation therapy +/- chemotherapy for stage II-III NSCLC from 2012 to 2022 across a statewide consortium. Logistic regression models were used to characterize the risk of grade 2 + and 3 + esophagitis as a function of dosimetric and clinical covariates. Multivariate regression models were fitted to predict the 50 % risk of grade 2 esophagitis and 3 % risk of grade 3 esophagitis.

RESULTS

Of 1760 patients, 84.2 % had stage III disease and 85.3 % received concurrent chemotherapy. 79.2 % of patients had an ECOG performance status ≤ 1. Overall rates of acute grade 2 + and 3 + esophagitis were 48.4 % and 2.2 %, respectively. On multivariate analyses, performance status, mean esophageal dose (MED) and minimum dose to the 2 cc of esophagus receiving the highest dose (D2cc) were significantly associated with grade 2 + and 3 + esophagitis. Concurrent chemotherapy was associated with grade 2 + but not grade 3 + esophagitis. For all patients, MED of 29 Gy and D2cc of 61 Gy corresponded to a 3 % risk of acute grade 3 + esophagitis. For patients receiving chemotherapy, MED of 22 Gy and D2cc of 50 Gy corresponded to a 50 % risk of acute grade 2 + esophagitis.

CONCLUSIONS

Performance status, concurrent chemotherapy, MED and D2cc are associated with acute esophagitis during definitive treatment of NSCLC. Models that quantitatively account for these factors can be useful in individualizing radiation plans.

Baseline shift corrections towards the heart: External validation of the impact on survival in early-stage NSCLC patients

PURPOSE

To externally validate Johnson-Hart et al. findings: the association of tumor baseline shifts towards the heart with overall survival (OS) in SBRT for NSCLC. Further analysis included investigating the presence of interfractional heart baseline shifts and the association of OS with heart dose change during treatment.

METHODS

Data from 416 SBRT early-stage NSCLC patients was collected. Pearson's correlations (PCCs) between clinical variables and treatment-averaged tumor shifts towards/away from the heart were explored. Validation of published multivariable Cox model was performed. PCCs between heart and tumor baseline shifts were analyzed. Dose accumulation was performed following daily CBCT-to-pCT deformable registration. Maximum heart dose (D0) was computed for planned and accumulated doses. Differences in OS according to shifts towards/away from the heart or D0 increase/decrease were analyzed. Significant D0 differences between patients with D0 increase/decrease and different tumor locations were explored.

RESULTS

Tumor shifts towards/away from the heart showed no significant association with OS (p = 0.91). Distance between PTV and heart correlated significantly (PCC = 0.18) with shifts to the heart. Cox model did not validate in our cohort. Heart presented baseline shifts positively correlated with tumor baseline shifts in all three directions (PCC ≥ 0.38; p < 0.001). Counterintuitively, patients experiencing increased D0 during treatment showed significantly better OS (p = 0.0077). Upper-lobe tumor patients with increased D0 had lower D0 than those with decreased D0 (right-upper-lobe p ≤ 0.018).

CONCLUSIONS

In our SBRT cohort, the shifts towards the heart were not associated with worse OS. Moderate correlations were found between tumor and heart baseline shifts in each direction. Moreover, the distance between the PTV and the heart showed a significant correlation with shifts to the heart.

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

AIMS

Cardiac disease is a dose-limiting toxicity in non-small cell lung cancer radiotherapy. The dose to the heart base has been associated with poor survival in multiple institutional and clinical trial datasets using unsupervised, voxel-based analysis. Validation has not been undertaken in a cohort with individual patient delineations of the cardiac base or for the endpoint of cardiac events. The purpose of this study was to assess the association of heart base radiation dose with overall survival and the risk of cardiac events with individual heart base contours.

MATERIALS AND METHODS

Patients treated between 2015 and 2020 were reviewed for baseline patient, tumour and cardiac details and both cancer and cardiac outcomes as part of the NI-HEART study. Three cardiologists verified cardiac events including atrial fibrillation, heart failure and acute coronary syndrome. Cardiac substructure delineations were completed using a validated deep learning-based autosegmentation tool and a composite cardiac base structure was generated. Cox and Fine-Gray regressions were undertaken for the risk of death and cardiac events.

RESULTS

Of 478 eligible patients, most received 55 Gy/20 fractions (96%) without chemotherapy (58%), planned with intensity-modulated radiotherapy (71%). Pre-existing cardiovascular morbidity was common (78% two or more risk factors, 46% one or more established disease). The median follow-up was 21.1 months. Dichotomised at the median, a higher heart base Dmax was associated with poorer survival on Kaplan-Meier analysis (20.2 months versus 28.3 months; hazard ratio 1.40, 95% confidence interval 1.14-1.75, P = 0.0017) and statistical significance was retained in multivariate analyses. Furthermore, heart base Dmax was associated with pooled cardiac events in a multivariate analysis (hazard ratio 1.75, 95% confidence interval 1.03-2.97, P = 0.04).

CONCLUSIONS

Heart base Dmax was associated with the rate of death and cardiac events after adjusting for patient, tumour and cardiovascular factors in the NI-HEART study. This validates the findings from previous unsupervised analytical approaches. The heart base could be considered as a potential sub-organ at risk towards reducing radiation cardiotoxicity.

Death without progression as an endpoint to describe cardiac radiation effects in locally advanced non-small cell lung cancer

Background and purpose

Prior studies have examined associations of cardiovascular substructure dose with overall survival (OS) or cardiac events after chemoradiotherapy (CRT) for non-small cell lung cancer (NSCLC). Herein, we investigate an alternative endpoint, death without cancer progression (DWP), which is potentially more specific than OS and more sensitive than cardiac events for understanding CRT toxicity.

Materials and methods

We retrospectively reviewed records of 187 patients with locally advanced or oligometastatic NSCLC treated with definitive CRT from 2008 to 2016 at a single institution. Dosimetric parameters to the heart, lung, and ten cardiovascular substructures were extracted. Charlson Comorbidity Index (CCI), excluding NSCLC diagnosis, was used to stratify patients into CCI low (0-2; n = 66), CCI intermediate (3-4; n = 78), and CCI high (≥5; n = 43) groups. Primary endpoint was DWP, modeled with competing risk regression. Secondary endpoints included OS. An external cohort consisted of 140 patients from another institution.

Results

Median follow-up was 7.3 years for survivors. Death occurred in 143 patients (76.5 %), including death after progression in 118 (63.1 %) and DWP in 25 (13.4 %). On multivariable analysis, increasing CCI stratum and mean heart dose were associated with DWP. For mean heart dose ≥ 10 Gy vs < 10 Gy, DWP was higher (5-year rate, 16.9 % vs 6.7 %, p = 0.04) and OS worse (median, 22.9 vs 34.1 months, p < 0.001). Ventricle (left, right, and bilateral) and pericardial but not atrial substructure dose were associated with DWP, whereas all three were inversely associated with OS. Cutpoint analysis identified right ventricle mean dose ≥ 5.5 Gy as a predictor of DWP. In the external cohort, we confirmed an association of ventricle, but not atrial, dose with DWP.

Conclusion

Cardiovascular substructure dose showed distinct associations with DWP. Future cardiotoxicity studies in NSCLC could consider DWP as an endpoint.

Associations between cardiac irradiation and survival in patients with non-small cell lung cancer: Validation and new discoveries in an independent dataset

INTRODUCTION

In 'IDEAL-6' patients (N = 78) treated for locally-advanced non-small-cell lung cancer using isotoxically dose-escalated radiotherapy, overall survival (OS) was associated more strongly with VLAwall-64-73-EQD2, the left atrial (LA) wall volume receiving 64-73 Gy equivalent dose in 2 Gy fractions (EQD2), than with whole-heart irradiation measures. Here we test this in an independent cohort 'OX-RT' (N = 64) treated routinely.

METHODS

Using Cox regression analysis we assessed how strongly OS was associated with VLAwall-64-73-EQD2, with whole-heart volumes receiving 64-73 Gy EQD2 or doses above 10-to-70 Gy thresholds, and with principal components of whole-heart dose-distributions. Additionally, we tested associations between OS and volumes of cardiac substructures receiving dose-ranges described by whole-heart principal components significantly associated with OS.

RESULTS

In univariable analyses of OX-RT, OS was associated more strongly with VLAwall-64-73-EQD2 than with whole-heart irradiation measures, but more strongly still with VAortV-29-38-EQD2, the volume of the aortic valve region receiving 29-38 Gy EQD2. The best multivariable OS model included LA wall and aortic valve region mean doses, and the aortic valve volume receiving ≥38 Gy EQD2, VAortV-38-EQD2. In a subsidiary analysis of IDEAL-6, the best multivariable model included VLAwall-64-73-EQD2, VAortV-29-38-EQD2, VAortV-38-EQD2 and mean aortic valve dose.

CONCLUSION

We propose reducing heart mean doses to the lowest levels possible while meeting protocol dose-limits for lung, oesophagus, proximal bronchial tree, cord and brachial plexus. This in turn achieves large reductions in VAortV-29-38-EQD2 and VLAwall-64-73-EQD2, and we plan to closely monitor patients with values of these measures still >0% (their median value in OX-RT) following reduction.

Impact of Cardiac Dose on Overall Survival in Lung Stereotactic Body Radiotherapy (SBRT) Compared to Conventionally Fractionated Radiotherapy for Locally Advanced Non-Small Cell Lung Cancer (LA-NSCLC)

PURPOSE

To examine possible association between heart irradiation and Overall Survival (OS) in lung SBRT patients and to compare observed associations with cardiac toxicity models previously derived in LA-NSCLC patient studies.

MATERIALS AND METHODS

197 Patients treated with lung SBRT at Mayo Clinic Arizona were selected for this IRB-approved study. Multivariate Cox model with Akaike Information Criterion (AIC) was used to select patient specific covariates associated with OS. Heart dosimetry was represented by VD indices, which is a percentage of volume exposed to dose D or greater. Multivariate Cox models with patient specific covariates and single VD index per model was used to find a range of doses which were predictive for OS. A digital subdivision of the heart was further used to determine the spatial distribution of doses which were predictive for OS. A coarse subdivision divided heart into 4 segments, while the fine subdivision divided heart into 64 segments. Knowledge constrained Fused Lasso operator was used to derive a more complete model which correlated heart dosimetry with OS. Results of statistical analysis were compared to predictions of a model of cardiac toxicity in LA-NSCLC patients.

RESULTS

Higher age (p < 0.001), higher stage (p < 0.001) and squamous cell histology (p = 0.001) were associated with reduced OS. Whole heart DVH analysis did not reveal associations between heart irradiation and reduced OS. Coarse subdivision of the heart into four segments revealed that the irradiation of two inferior segments of the heart with low doses was associated with reduced OS, V 2Gy in the right-inferior segment (HR = 1.012/1%, p = 0.02), and V 1Gy in the left-inferior segment (HR = 1.01/1%, p = 0.04). Maximum dose in the right-inferior segment of the heart was also associated with reduced OS (HR = 1.02/Gy, p = 0.02). Fine subdivision of the heart into 64 segments revealed that approximately 25% of heart volume in the inferior part of the heart (15/64 segments), when irradiated to doses in the 1 Gy - 5 Gy range, were predictive for reduced OS (HR = 1.01/1%, p = 0.01). A previously derived model of cardiac toxicity in LA-NSCLC patients did not predict a reduction of OS due to heart irradiation in lung SBRT patients, because of relatively low doses to the heart in most lung SBRT patients.

CONCLUSIONS

Doses lower than 5 Gy in the inferior segments of the heart may be associated with reduced overall survival in patients treated for lung lesions with SBRT. Stage and histology of the disease, as well as patients' age, were also associated with overall survival. Comparisons of cardiac toxicity patterns in LA-NSCLC patients and lung SBRT patients suggest different etiology of cardiac toxicity in the two groups.