To explore feasibility of applying stereotactic body radiation therapy (SBRT) to irradiate the antrum of the four pulmonary veins while protecting the nearby critical organ such as the esophagus. Twenty patients who underwent radiofrequency catheter ablation for atrial fibrillation were selected. For each patient, the antrum of the four pulmonary veins was identified as the target volumes on the precatheterization contrast CT scan. On each CT scan, the esophagus, trachea, heart, and total lung were also delineated with the esophagus being identified as the critical organ. For each patient, three treatment plans were designed with 0, 2, and 5 mm planning margins to the target, while avoiding overlaps with 2 mm expansion of esophagus, defined as planning organ-at-risk volume (PRV). Using three non-coplanar volumetric modulated arcs (VMAT), 60 plans were created to deliver a prescription dose of 50 Gy in five fractions, following the SBRT dose regimen for central lung tumors. With greater than 97% of the planning target volumes receiving the prescription doses, we examined dosimetry to 0.03 cm3 and 5 cm3of the esophagus PRV volume, as well as other contoured structures. The average PTV- 0 mm, PTV- 2 mm, and PTV- 5 mm volumes were 3.05 ± 1.90 cm3, 14.70 ± 5.00 cm3, and 40.85 ± 10.20 cm3, respectively. With three non-coplanar VMAT arcs, the average conformity indices (ratio of isodose volume and the PTV volume) for the PTV- 0 mm, PTV- 2 mm and PTV- 5 mm were 4.81 ± 2.0, 1.71 ± 0.19, and 1.23 ± 0.08, respectively. If the patients can be treated under breath hold, using 2 mm planning margins to account for cardiac motion, all plans met the maximum dose limits <50 Gy to 0.03 cm3 and 17 plans (85%) met <27.5 Gy to 5 cm3 of the esophageal PRVs. For PTV- 5 mm plans, 19 plans met the maximum dose limit <50 Gy to 0.03 cm3 and only 2 plans met the maximum dose limit <27.5 Gy to 5 cm3of the esophageal PRV. The average endpoint doses of selected structures are listed in Table 1. The anatomical relationship between the antra of the four pulmonary veins and the esophagus varies from patient to patient. Adding 2 mm planning margins and 2 mm PRV to the esophagus can meet the dose constraints developed for SBRT central lung tumors. Future studies are needed to verify the safety of these doses and planning margins.ePoster Abstracts 1002; Table 1Average Endpoint Doses for Other Selected StructuresStructuresEndpoint0 mm Margin2 mm Margin5 mm MarginEsophagus-2 mmD0.03 cm3 (Gy)49.8 ± 5.347.0 ± 2.148.5 ± 1.5Esophagus-2 mmD5 cm3 (Gy)24.2 ± 4.825.3 ± 2.731.2 ± 2.5Whole-LungD100 cm3 (Gy)12.1 ± 2.514.6 ± 3.018.1 ± 3.2HeartDmean (Gy)7.2 ± 3.310.5 ± 3.313.1 ± 3.2TracheaD4 cm3 (Gy)12.3 ± 5.115.9 ± 6.620.3 ± 8.1 Open table in a new tab