Positive association between heart dosimetry parameters and a novel cardiac biomarker, solubleST‐2, in thoracic cancer chest radiation

Abstract Background Early screening and diagnosis of radiation‐induced heart disease (RIHD) is difficult in patients with chest radiation exposure. sST‐2 is involved in myocardial stress or injury. We evaluated the relationship between heart dose parameters and sST‐2 changes in chest malignant tumor patients who received chest radiation. Methods We prospectively collected thoracic malignancy cancer patients who had received chest radiotherapy. Heart dosimetry parameters were extracted from the treatment planning system. sST‐2 was measured at baseline, the middle stage, and after radiotherapy (recorded as pre‐ST‐2, mid‐ST‐2, and post‐ST‐2). sST‐2 change rate was calculated. Scatter plots showed the relationship between cardiac dose parameters and ST‐2 change rate. Multiple regression was used to analyze the relationship between cardiac dose parameters and ST‐2 change rate. Results Totally, 60 patients were enrolled. The mean V5, V10, V20, V30, V40, and MHD was 60.93 ± 27.79%, 51.43 ± 25.44%, 39.17 ± 21.75%, 28.07 ± 17.15%,18.66 ± 12.18%, and 18.60 ± 8.63 Gy, respectively. The median M‐LAD was 11.31 (IQR 3.33‐18.76) Gy. The mean pre‐ST‐2, mid‐ST‐2, and post‐ST‐2 was 5.1 ± 3.8, 6.4 ± 3.9, and 7.6 ± 4.4, respectively. sST‐2 was elevated with thoracic irradiation (P < .001). Multivariate linear regression analyses showed that V5, V10, V20, and MHD were independently and positively associated with ST‐2 change rate (β = .04, .04, .04, and .10, respectively, all P < .05). Conclusion Serum sST‐2 levels were elevated over time during radiotherapy. V5, V10, V20 and MHD were independently and positively associated with the elevated ST‐2 change rate.


| INTRODUC TI ON
Thoracic radiotherapy (RT) is one of the main treatments for lung cancer, 1,2 esophageal cancer, 3 and thymoma. 4 Cardiotoxicity is a serious problem threatening the survival and quality of life of patients undergoing thoracic radiotherapy. 5 A large number of studies have shown that RIHD can occur in patients with breast cancer, childhood lymphoma, and other cancers decades after radiotherapy. [6][7][8] Until now, there was no standard diagnostic method for RIHD. Myocardial markers (including brain natriuretic peptide (BNP), pro-BNP, and cTnI), echocardiography, and cardiac magnetic resonance are common methods for diagnosing RIHD. 8,9 Early screening and diagnosis of RIHD are difficult in patients with radiation exposure.
ST-2 is a member of the interleukin-1 receptor family and includes transmembrane (ST-2L) and soluble ST-2 isoforms (sST-2). 10 IL-33 is a specific ligand of ST-2L, forming the IL-33/ST-2 signaling pathway, which is involved in myocardial stress or injury. 11,12 Multiple studies revealed that elevated sST-2 concentration is involved in various heart diseases, such as heart failure, [13][14][15] atrial fibrillation, 16 heart transplant recipients, 17,18 chronic kidney disease-induced cardiac remodeling, 19 and myocardial infarction. 11,20 The guidelines for heart failure management issued by ACCA/AHA in 2013 recommend soluble ST-2 as an additional indicator of risk stratification in patients with acute and chronic heart failure. 13 Heart radiation exposure can lead to vascular endothelial cell damage and vascular inflammatory reactions, resulting in interstitial ischemic fibrosis caused by thrombosis or inflammatory reactions. A study demonstrated that sST-2 levels in workers from the nuclear industry were significantly higher (fivefold) than the control group without exposure history. 21 When patients receive chest radiotherapy, the heart is exposed to large doses of X-rays in a short duration, especially in central lung tumors and esophageal cancer. However, the effect of chest radiation on sST-2 and whether changes in sST-2 levels are associated with cardiac doses was unclear.
In this study, we examined sST-2 levels in the serum of patients receiving high-dose radiotherapy for thoracic malignancies. We evaluated early changes in serum sST-2 levels during thoracic radiotherapy and determined associations between heart dosimetry parameters and ST-2 change rate. Inclusion criteria were as follows: age >18 years, Eastern Cooperative Oncology Group performance status 0-2, and adequate hematologic, hepatic, and renal function. Exclusion criteria were as follows: the presence of another primary cancer (excluding skin cancer beyond 5 years), thoracic radiation historically, malignant pericardial effusion, uncontrolled angina pectoris, myocardial infarction <3 months before enrollment, interstitial pneumonia, active lung fibrosis, or severe cachexia. All enrolled patients provided consent and the study was approved by the Ethics Committee of the Second Affiliated Hospital of Nanchang University.

| Serum sST-2 and BNP array
Blood samples were collected in tubes with EDTA and serum was separated by centrifugation for 10 min at 600 × g. The serum samples were stored at −80°C for later use. sST-2was determined using a high-sensitivity enzyme-linked assay (ELISA) kit (Presage ST-2 assay; Critical Diagnostics) according to the manufacturer's procedures.
sST-2 levels were evaluated after determining the optical density of the samples at 450 nm (Thermo Scientific Microplate Reader, Varioskan LUX). BNP was detected in our clinical laboratory collected in medical record system.

| Cardiac echocardiography
Cardiac echocardiographic examinations were performed using GE Vivid (GE Healthcare, Vivid E9) by experienced physicians who were blinded to all treatment data. LVEF was collected before and after radiotherapy.

| Irradiation
All patients received intensity-modulated or volumetric-modulated RT (IMRT or VMRT) using an Elekta linear accelerator (Elekta Versa HD) in a supine position fixed with mask or vacuum bag.
The targets and organs at risk (OAR), including the heart, were contoured by the same physician, and the treatment plan was designed by a specific physician. The dose of normal tissues was constrained (lung of V 20 <32%, V 30 <20%, heart of V 40 <30%).
Heart dosimetry parameters, including V 5 , V 10 , V 20 , V 30 , V 40, the mean dose of the heart (MDH), and the mean dose of the left anterior descending coronary artery (M-LAD), were extracted from the dose-volume histogram (DVH) curves in the Monaco treatment planning system (Elekta Versa HD).

| Statistical analysis
Data are presented as mean ± SD or median (interquartile range, IQR) for continuous variables and as frequency (%) for categorical variables. We used either two-tailed t test/paired t test or the Wilcoxon rank-sum test for comparison of two groups. ST-2 change rate was calculated by subtracting pre-ST-2 from post-ST-2 and then dividing it by pre-ST-2. Multivariate linear regression analyses were used to assess the β and 95% confidence interval (CI) of cardiac dose parameters associated with ST-2 change rate, with adjustment for major covariables including age, gender, smoking, history of coronary disease, diabetes mellitus, hypertension, chemotherapy, and surgery. The smooth curve fitting (penalized spline method) was used to characterize the shape of the associations between heart dose parameters and ST-2 change rate. All analyses were performed using the statistical package R (http://www.R-proje ct.org, The R Foundation) and Empower (R) (www.empow ersta ts.com; X&Y Solutions, Inc). A 2-tailed P < .05 was considered statistically significant.

| Population characteristics
Demographic data in the study are shown in Table 1

| Association between heart dose parameters and levels of ST-2
The mean V 5 , V 10 , V 20 , V 30 (Figure 2).

| D ISCUSS I ON
We found that heart dose parameters in thoracic malignant tumor patients are associated with a change in ST-2 change rate, when they received chest RT. Our results showed that compared with baseline, ST-2 levels increased over time. However, compared with pre-LVEF levels, post-LVEF levels were not different, and the traditional cardiac biomarker BNP levels were also not changed. A positive association between heart dose parameters andST-2 change rate was found.
Despite the rapid progress in cancer screening, diagnosis, and treatment, treatment-related cardiovascular events such as radiation-induced cardiac injury remain unavoidable. 5   found no acute changes in LVEF in breast cancer patients with concurrent trastuzumab and breast radiation. In this study, although the heart dose was higher than in the Bian et al study, the post-LVEF levels were also not changed compared with baseline LVEF (pre-LVEF) levels. Interestingly, we found that sST-2 was increased during RT. Thus, sST-2 might be useful in detecting acute or subclinical cardiotoxicity.

TA B L E 2 Relationship between heart dose parameters and ST change rate in different models
Accumulated results from clinical studies have shown that high cardiac radiation dose is directly associated with RIHDs. 24,[27][28][29] Oncologists must also consider the rate of cancer control and the dose of cardiac radiation when formulating a RT regimen. In childhood cancer survivors, a large sample case control study revealed that heart failure often occurred in patients that received ≥30 Gy to the median volume of the heart. 30 In stage III non-small-cell lung cancer, different cardiac events were associated with distinct heart volume doses; for example, ischemic events were correlated with left ventricle and whole heart dose. 27 The mean V 5 , V 10 , V 20 , V 30

| CON CLUS ION
In conclusion, we showed that sST-2 levels were elevated during radiotherapy over time in patients with thoracic malignant tumors when they received chest RT, and V 5 , V 10 , V 20 , and MHD were independently and positively associated with ST-2 change rate.

ACK N OWLED G EM ENTS
The authors would like to thank Zou Bing of the Radiotherapy Center for his help in collecting radiation heart dose parameters and Hu Lihua, Department of Cardiovascular Medicine, for his help in part of data processing.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no conflict of interest.  The study was consented by all the enrolled patients and the Ethics Committee of the second affiliated hospital of Nanchang University.

DATA AVA I L A B I L I T Y S TAT E M E N T
The datasets used and analyzed during the study are available from the corresponding author on reasonable request, except private information of participants.