132 Background: 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/beta ratio = 3) of 222.7 Gy. Mean volume of the GTV and PTV were 26.1 and 75.1 mL, respectively. Mean follow-up was 25.5 months. The mean volume of the SAN was 0.37 mL. Average max dose and mean dose to the SAN were 24.7 and 70.7 Gy, respectively. Of the 13 patients whose treatment imparted significant dose to the SAN, one patient without prior arrhythmia developed symptomatic SAN dysfunction requiring pacemaker placement at 6 months after completion of treatment. The sinoatrial node of the patient received a maximum dose of 44.8 Gy in 4 fractions, correlated with an acute BED (alpha/beta ratio = 10) of 90 Gy and late BED (alpha/beta ratio = 3) of 194.1 Gy, and a mean dose of 35.5 Gy in 4 fractions, correlated with an acute BED (alpha/beta ratio = 10) of 71 Gy and late BED (alpha/beta ratio = 3) of 153.8 Gy. This was the third highest max dose and second highest mean dose to SAN in the cohort. Conclusions: We report sinoatrial node dysfunction as a potential toxicity of SABR in the chest for non-small cell lung cancer. Caution is advised when treatment imparts significant dose to the sinoatrial node.
The Role of the Calcium and the Voltage Clocks in Sinoatrial Node Dysfunction