LAUSR

132Background: Sinoatrial node (SAN) injury following stereotactic ablative radiation therapy (SABR) in the chest has not been reported in the literature. We report SAN dysfunction as a potential toxicity of SABR in the chest. Methods: We examined the clinical courses and SABR plans of 47 patients treated for T1 or T2 non-small cell lung cancer of the right upper lobe, middle lobe, lower lobe, or hilum. After developing a contouring atlas for the SAN, based upon the junction between the superior vena cava and the right atrium, dose to the SAN was retrospectively determined for each patient. We identified 13 patients whose treatment imparted significant dose to the SAN, as defined by the SAN encompassed within the 10% prescription isodose (IDL) line. Biologically effective doses (BED), acute and chronic, were correlated with SAN toxicity. Results: Patients underwent SABR to the right lung to a dose of 40-50 Gy in 4 or 5 fractions, with mean acute BED (alpha/beta ratio = 10) of 100.2 Gy and late BED (alpha/...