PO-01-050 STRUCTURAL CARDIAC CHANGES DETECTED BY MRI AFTER STEREOTACTIC BODY RADIOTHERAPY FOR TARGETS IN CLOSE PROXIMITY TO THE HEART

Abstract

Stereotactic body radiation therapy (SBRT) has become a standard of care for inoperable early-stage non-small cell lung cancer and in case of pulmonary oligometastases. Recent studies indicate that incidental irradiation of the heart may be associated with an increased risk of non-cancer-related deaths. This study aims to assess and examine structural cardiac changes following peri- and myocardial SBRT using a systematic cardiac follow-up protocol including cardiac magnetic resonance (CMR) imaging. For 1485 patients treated with local-ablative SBRT from January 2014 to February 2022 at our institution, the distance between the planning target volume (PTV) and the heart was measured. Forty-eight out of 134 patients treated in close proximity (<2cm) to the heart were alive at follow-up. Of those, 20 were randomly invited to undergo a structured cardiac follow-up protocol including CMR. Ten patients consented to participate and underwent a structural follow-up protocol. Registration of CMR image data and the SBRT treatment plan was performed to examine a possible correlation between the dose delivered to the myocardium and structural cardiac changes assessed by CMR. Among the 10 participating patients, the most common primary tumors were non-small cell lung cancer (n=3) and small-cell lung cancer (n=2) (Table 1). Five patients presented with pre-SBRT cardiovascular comorbidities. Seven patients received SBRT for pulmonary or vertebral metastases and three patients for primary lung cancer with a median dose of 42.5 Gy (30.0-48.0 Gy) in 3-10 fractions. The mean heart dose (Dmean) and maximum heart dose (Dmax) were 4.9 Gy (0.7-8.4 Gy) and 36.2 Gy (8.3 – 64.1 Gy), respectively. On CMR, five patients showed myocardial alterations, such as late gadolinium enhancement and edema after a median follow-up time of 5.6 years (0.1-6.3 years) as shown in Figure 1. In patients with structural changes of the myocardium the median distance between the treated lesion and myocardium with 0.0 (0.0-1.08) cm vs. 1.4 (0.41-2.0) cm was significantly lower (p=0.015). Additionally, patients with structural changes on CMR showed significantly higher Dmax (135.4 Gy vs. 25.4 Gy, p=0.009), Dmean (4.4 Gy vs. 3.4 Gy, p=0.05). In this pilot study, patients treated with SBRT for pulmonary targets with PTV overlapping the heart showed structural changes of the myocardium in CMR. The presence of structural changes correlates with higher heart doses.