Abstract
BACKGROUND: Stereotactic arrhythmia radiotherapy (STAR) is a highly promising bail-out treatment for patients with therapy-refractory ventricular tachycardia (VT). Despite precise, noninvasive targeting of the pro-arrhythmic area, surrounding healthy cardiac tissue inadvertently receives low-dose radiation. There is a historical notion that collateral cardiac damage from radiation of extra-cardiac structures can cause heart failure and arrhythmias. In the HALO trial, where non-small cell lung cancer (NSCLC) patients treated with stereotactic ablative radiotherapy (SABR) received relatively low-dose radiotherapy to the heart, detailed cardiac safety after radiotherapy was therefore evaluated. OBJECTIVE: The aim of this study was to prospectively evaluate cardiac function after collateral radiotherapy on the heart in patients with NSCLC treated with SABR. METHODS: The HALO trial was a prospective observational trial evaluating cardiac adverse effects in patients treated with SABR for early stage NSCLC. Patients with a tumour within 3cm of the pericardium were eligible to participate. The mean radiotherapy dose per segment was calculated by semi-automated angulation and segmentation using an in-house developed tool. The heart was segmented according to the AHA 17-segment model. Patients underwent cardiac magnetic resonance imaging (CMR) pre-treatment, 3 and 12 months after treatment. CMR strain-analysis was conducted by two independent observers using cvi42 software. Longitudinal, radial and circumferential strain were measured both globally and segmentally and evaluated for dose-dependent effects. RESULTS: Ten patients were included in this study. Two patients dropped out before first follow-up and were not included in this analysis. Median age was 66 years (range 58-81) and four were male (50%). Median distance between the tumour and pericardium was 0.46cm (range 0.00-2.80). Patients were treated with 8 fractions of 7.0-7.5 Gy (n=6), 5 fractions of 11.0 Gy (n=1) or 3 fractions of 18.0 Gy (n=1). Median global cardiac radiotherapy dose was 6.7 Gy (range 0.1-17.9). Pre-treatment, median left ventricular ejection fraction as measured on CMR was 65% (range 40-75), global longitudinal strain was -15% (-20 - -9), global circumferential strain was -17% (-26 - -9) and global radial strain was 28% (11-60). These did not significantly change comparing 3 months and 12 months after treatment with pre-treatment. As can be appreciated from Table 1, there were no dose-dependent effects on segmental longitudinal, radial and circumferential strain both 3 months or 12 months after SABR. There were no ventricular arrhythmias observed during follow-up. CONCLUSION: In this small study, collateral radiotherapy in patients with NSCLC treated with SABR did not significantly alter cardiac function as measured on CMR, and no relevant pro-arrhythmic effects were observed during short term follow-up. Extending the research into a larger dataset is warranted. [Figure: see text]