Quantification of variations in intra-fraction motion of esophageal tumors over the course of neoadjuvant chemoradiotherapy based on cine-MRI

To noninvasively quantify variation in intra-fraction motion of esophageal tumors over the course of neoadjuvant chemoradiotherapy (nCRT) using 2D tine-magnetic resonance imaging (MRI) series. Patients treated with nCRT for esophageal cancer underwent six MRI scans. Scans were acquired prior to the start of nCRT, followed by weekly MRI scans during nCRT. Cine-MRI series were acquired in the coronal and sagittal plane (approximate to 1.6 Hz). To be able to quantify intra-fraction motion over a longer time period, a second cine-MRI series was performed after 10 min. Tumor motion was assessed in cranio-caudal (CC), anterior-posterior (AP) and left-right (LR) direction. Motion patterns were analyzed for the presence of deep inhales and tumor drift. A total of 232 cine-MRI series of 20 patients were analyzed. The largest tumor motion was found in CC direction, with a mean peak-to-peak motion of 12.7 mm (standard deviation [SD] 5.6), followed by a mean peak-to peak motion in AP direction of 3.8 mm (SD 2.0) and in LR direction of 2.7 mm (SD 1.3). The CC intra-fraction tumor motion can differ extensively between and within patients. Deep inhales were present in six of 232 scans (3%). After exclusion of these scans, mean CC peak-to-peak motion was12.3 mm (SD 5.2). Correction for tumor drift showed a further reduction to 11.0 mm (SD 4.6). Despite correction for tumor drift, a large variation in tumor motion occurred within patients during treatment. Mean tumor drift during the 10 min interval between the two series was 1.5 mm (SD 1.8), with a maximum of 11.6 mm. Intra-fraction tumor motion was found to be highly variable between and within patients with esophageal cancer over the course of nCRT. Correction for deep inhales and tumor drift reduced peak-to-peak motion. The stochastic nature of both deep inhales and tumor drift indicates that realtime tumor motion management during radiotherapy is a prerequisite to safely reduce treatment margins.