Electrocardiogram-gated Computed Tomography with Coronary Angiography for Cardiac Substructure Delineation and Sparing in Patients with Mediastinal Lymphomas Treated with Radiotherapy

Abstract Purpose (1) Demonstrate feasibility of electrocardiogram-gated computed tomography with coronary angiography (E-CTA) in treatment planning for mediastinal lymphoma and (2) Assess whether inclusion of cardiac substructures in the radiation plan optimization (CSS optimization) results in increased cardiac substructure sparing. Methods Patients with mediastinal lymphomas requiring radiotherapy were prospectively enrolled in an observational study. Patients completed a treatment planning CT and E-CTA in the deep inspiration breath hold (DIBH) position. Avoidance structures (e.g. coronary arteries and cardiac valves) were created in systole and diastole and then merged into a single planning organ at risk volume, based on a cardiac substructure contouring atlas. In the photon cohort, two volumetric modulated arc therapy (VMAT) plans were created per patient with and without CSS optimization. Dosimetric endpoints were compared. Results In the photon cohort, 7 patients were enrolled. For all 7 patients, the treating physician elected to use the CSS optimization plan.. At the individual level, two patients had reductions of 10.8 and 16.2% of the RCA receiving at least 15 Gy and one had a reduction in 9.6% of the LAD receiving 30 Gy. No other differences for coronary arteries were detected between 15-30 Gy. Conversely, 5 of 7 patients had >10% reductions in dose between 15-30 Gy to at least one cardiac valve. The greatest reduction was 22.8% of the aortic valve receiving at least 30 Gy for one patient. At the cohort level, the maximum, mean, and 5 Gy increment analyses were nominally similar between planning techniques for all cardiac substructures and the lungs. Conclusions Cardiac substructure delineation using E-CTA was feasible and inclusion in optimization led to modest improvements in sparing of radiosensitive cardiac substructures for some patients.