Organ motion in different time aspects in esophageal cancer radiotherapy - is a novel fiducial marker feasible?

Introduction: A novel fiducial marker was explored for use in image-guided radiotherapy (IGRT) of esophageal cancer patients by characterizing inter- and intra-fractional organ motion. Material and methods: Twelve esophageal cancer patients proposed for radiotherapy participated in this pilot-study. Makers (1-6 per patient) were implanted EUS- guided prior to radiotherapy planning CT (CTp) with additional 4DCT, and the patients received IGRT (23-33 fractions, 41.4-66.0 Gy) with daily cone beam computed tomography (CBCT, n=302) and/or orthogonal planar images (2D/2D, n=61) and a repeated CT- and 4DCT the last treatment week. Marker presence, planning target volume (PTV) coverage, centroid position and extreme positions on CBCT were recorded per patient and -treatment fraction. Inter- and intra-fractional motion were characterized, in all patients and grouped according to marker location. Results: At treatment end, 92% of markers visible at CTp were still present. The PTV accounted for marker variation in >95% of treatment fractions for 92% of the patients. Overall 3D inter-fractional variation was >1cm in 23% and >0.5cm in 58% of the markers. Median (IQR) intra-fractional motion of all markers was 1.2 cm (0.4 cm) in the longitudinal, 0.11 cm (0.51 cm) in the ventral and 0.0 cm (0.13 cm) in the lateral direction. Conclusion: The use of the investigated fiducial marker may be beneficial for IGRT in esophageal cancer as the marker loss during radiotherapy was limited. Inter- and intra-fractional variation was substantial with largest motion in the longitudinal direction and more pronounced in the caudal part of esophagus