To evaluate inter- and intra-fraction esophageal motion in the right-left (RL) and anterior-posterior (AP) directions using computed tomography (CT) in esophageal cancer patients.
Methods and Materials
Eight patients underwent CT simulation and CT-on-rails imaging before and after radiotherapy. Inter-fraction displacement was defined as differences between pre-treatment and simulation images. Intra-fraction displacement was defined as differences between pre- and post-treatment images. Images were fused using bone registries, adjusted to the carina. The mean, average of the absolute, and range of esophageal motion were calculated in RL and AP directions, above and below the carina.
Thirty-one CT image sets were obtained. The incidence of esophageal inter-fraction motion ≥5 was 24% and ≥10 mm was 3%; intra-fraction motion ≥ 5mm was 13% and ≥10 mm was 4%. The average RL motion was 1.8±5.1 mm, favoring leftward movement, and the average AP motion was 0.6±4.8 mm, favoring posterior movement. Average absolute motion was 4.2 mm or less in RL and AP directions. Motion was greatest in the RL direction above the carina. Coverage of 95% of esophageal mobility requires 12mm left, 8mm right, 10mm posterior, and 9mm anterior margins.
In all directions, the average of the absolute inter-fraction and intra-fraction displacement was 4.2 mm or less. These results support a 12 mm left, 8 mm right, 10 mm posterior, and 9 mm anterior margin for ITV and can guide margins for future IMRT trials to account for organ motion and set up error in 3-dimesional planning.