Qiu B, et al. Pract Radiat Oncol 2020.
BACKGROUND: and Purpose: To quantify the interfractional motion of the esophagus during fractionated radiotherapy for locally advanced non-small cell lung cancer (NSCLC).
MATERIALS AND METHODS: We registered simulation four-dimensional computed tomography (4DCT) and daily cone beam CT (CBCT), and documented the motion of the esophagus centroid at 5mm-interval slices in right-left (RL) and anterior-posterior (AP) directions. Oral barium sulfate was administrated during CBCT to help localize the esophagus. Thirty-five patients were enrolled. Thirty-five 4DCT scans, 595 CBCT scans and 25,970 slices were analyzed. The slice-derived motion values for all patients were presented as 2.5∼97.5 percentiles and ranges stratified by segments. The magnitude of motion for each individual patient was defined as the standard deviation (SD) of daily motion values stratified by segments. Correlations between the magnitude of motion and clinical variables were explored.
RESULTS: The 2.5∼97.5 percentiles of RL/AP motion were -4.2∼7.1/-4.4∼5.1, -10.3∼6.0/-4.3∼3.8, -8.7∼5.5/ -6.4∼2.8 and -9.1∼4.7/-5.8∼3.3mm for cervical, proximal, middle and distal thoracic esophagus respectively. The interfractional motion was direction- and location-dependent. The magnitude of RL motion was greater than that of AP motion for the four segments (p<0.05). In RL direction, the magnitude of motion was greater for middle thoracic esophagus than for cervical (median SD, 2.7 vs. 2.0 mm, p=0.001) and proximal thoracic esophagus (median SD, 2.7 vs. 2.1 mm, p=0.002). Patients with right lung tumor and bulky lymph nodes tended to display greater RL esophageal motion.
CONCLUSIONS: The interfractional motion of the esophagus can be considerable during radiotherapy in locally advanced NSCLC, especially for middle thoracic esophagus in RL direction. Strategies to minimize the effect of interfractional esophageal motion on dosimetry should be considered.