Myocardial FDG Uptake Changes After Thoracic Radiotherapy With Cardiac Exposure

Background: To evaluate global and regional myocardial 18 F-FDG uptake before and after thoracic radiotherapy (RT) for esophageal cancer under standardized fasting conditions, and to compare metabolic changes between heart-exposed and heart-spared patients. Patients and Methods: Sixty-three patients underwent paired pre-RT and post-RT FDG PET/CT following at least 12 hours of fasting. Patients were classified as heart-exposed (n = 47) or heart-spared (n = 16) based on RT treatment-field documentation. Cases with visually diffuse physiological myocardial uptake were excluded, yielding 30 nondiffuse cases (heart-exposed, n = 20; heart-spared, n = 10). Left ventricular (LV) SUVmax and regional SUVmean were analyzed using paired tests, and ΔSUVmax was compared between groups using the Mann–Whitney U test. Results: In the entire cohort (n = 63), LV SUVmax increased from 7.0 ± 5.4 pre-RT to 8.3 ± 6.3 post-RT without statistical significance ( P = 0.114). In nondiffuse cases, LV SUVmax increased significantly from 3.5 ± 1.1 to 4.5 ± 2.4 ( P = 0.016). Among heart-exposed nondiffuse patients, SUVmax increased significantly (3.4 ± 1.3–4.9 ± 2.8; P = 0.019), whereas no significant change was observed in heart-spared patients (3.5±0.8–3.7±0.9; P = 0.557). Regional analysis demonstrated a significant post-radiotherapy increase in septal wall SUVmean in heart-exposed patients, with a similar increasing trend observed in the inferior wall. Conclusions: FDG PET detects early, localized myocardial metabolic activation after thoracic RT in heart-exposed patients, whereas no significant change is observed in heart-spared patients, supporting its utility for early assessment of radiation-associated myocardial effects.