3664 - Retrospective Evaluation of Cardiac Functional Effects of Incidental Low-Dose Radiation from Lung SBRT
Presenter(s)
P. L. Wilson1, C. O'Driscoll1, R. Evans2, J. Moore1, L. Chang1, L. C. Cho1, and C. Rodriguez-Russo1; 1Department of Radiation Oncology, University of Minnesota Medical School, Minneapolis, MN, 2Clinical and Translational Science Institute, University of Minnesota, Minneapolis, MN
Purpose/Objective(s): Cardiac effects of incidental low dose radiation during thoracic SBRT are poorly defined. Higher cardiac radiation doses are linked to adverse outcomes such as ischemic heart disease, but preclinical data suggest low-dose radiation may modulate myocardial remodeling and improve function. We hypothesized that incidental low-dose cardiac radiation during lung SBRT may result in subclinical changes in left ventricular ejection fraction (LVEF).
Materials/Methods: A single institution retrospective review was performed of patients with primary lung cancer (ICD-10 C34) treated with SBRT at one institution between 2016 and 2025 who also received both pre- and post-treatment echocardiograms (echos) for any purpose. Baseline cardiac comorbidities and post-treatment major adverse cardiac events (MACEs) were recorded. Associations between cardiac dose received (measured EQD2, a/ß = 3), changes in LVEF, and baseline cardiac disease were evaluated using descriptive statistics, plots, and multivariate regressions with mean heart dose and baseline EF as covariates.
Results: Among all patients who received lung SBRT, 65 patients had recorded pre- and post-SBRT echos (54% male; median age 70, range 47-90). Most received 5-fraction SBRT (75%), with others receiving 1, 3, or 8 fractions. 17 patients (26%) had underlying heart failure and 44 patients (68%) had other underlying cardiac comorbidities at the time of SBRT. Median interval from pre-treatment echo to SBRT completion was 6.8 months (range 0.8–125.3), and from SBRT completion to post-treatment echo was 6.8 months (range 0.4–80.3). Median follow-up from SBRT completion to last follow-up was 27 months (range 3.9–111.8). 35 (54%) were deceased at last follow up. Average mean heart radiation dose was 181.2 ± 210 cGy EQD2 (median 96.8, IQR 21.9–294.3). 12 patients (18%) received systemic therapy between echos. Median LVEF change was 0 (range -32.5 to 20.0), mean 0.16 ± 7.57%. Post SBRT MACEs occurred in 9 patients (14%): MI (n = 1), cardiac arrest (n = 2), new arrhythmia (n = 3), transplanted sinus node dysfunction (n = 1), mitral valve endocarditis (n = 1), NSTEMI (n = 1). Mean heart dose was not significantly associated with LVEF change (? = -0.12, 95% CI -0.35 to 0.13, p = 0.34). Among subgroup analyses of the same relationship, no significant correlations were observed; for patients with underlying heart failure: ? = 0.07, 95% CI -0.42 to 0.54, p = 0.78 and other baseline cardiac comorbidities: ? = 0.08, 95% CI -0.37 to 0.22, p = 0.61.
Conclusion: Incidental mean cardiac radiation dose during lung SBRT was not statistically significantly associated with LVEF decline, overall or by baseline heart failure and underlying cardiac comorbidity subgroups. Future analyses will evaluate the effect of cardiac substructure doses and volumetric dose to clarify dose response relationships between cardiac exposure and LVEF. Overall, low-dose cardiac exposure from SBRT appears well-tolerated, and further study in at-risk populations is warranted.