P2.17-26 Quantifying the Interfractional Motion of the Esophagus During Radiation Therapy for Locally Advanced Non Small Cell Lung Cancer

Abstract

To quantify the interfractional motion of the esophagus during radiation therapy for locally advanced non small cell lung cancer using daily cone beam CT. The analysis of interfractional esophagus motion was performed on treatment planning 4DCT scans and daily CBCT acquired from 35 patients with stage IIIA/B NSCLC. The simulation CT and CBCT were fused using bone registries and adjusted to the carina. Interfractional motion of the esophagus in the right-left (RL) and anterior-posterior (AP) directions at levels of sternal notch (A), carina (B), 2.5 cm below the carina (C) and the left lower pulmonary vein (D) was recorded and analyzed respectively. A total of 612 CBCT image sets were obtained. The mean interfractional RL motion at level A, B, C and D was 0.5±2.9mm, -0.2±3.7mm, -0.5±3.9mm and -1.3±4.8mm, with the mean absolute value of 2.1±2.0mm, 2.7±2.6mm, 2.9±2.6mm and 3.4±3.6mm, respectively. The mean AP motion at level A, B, C and D was -0.3±2.0mm, 1.0±2.0mm, 1.3±2.2mm and 2.2±2.4mm, with the mean absolute value of 1.6±1.3mm, 1.7±1.6mm, 2.6±1.9mm and 3.4±3.6mm, respectively. Coverage of 95% of esophageal mobility requires 4.9 mm left, 4.4mm right, 3.1mm posterior and 3.7mm anterior margins at level A; 5.3 mm left, 6.5mm right, 4.5mm posterior and 1.9mm anterior margins at level B; 5.5 mm left, 7.2mm right, 4.8mm posterior, and 2.0mm anterior margins at level C; and 4.9 mm left, 7.9mm right, 6.3mm posterior, and 1.6mm anterior margins at level D. In RL and AP directions, the average of the absolute interfractional motion of the esophagus was 3.4mm or less at all the four levels. The interfractional motion was greatest at the level of left lower pulmonary vein. The absolute RL motion was greater than AP motion. These data helps to set margin for ITV for future IMRT trials to account for esophageal motion.