O114 TUMOR VOLUME REGRESSION DURING NEOADJUVANT CHEMORADIOTHERAPY FOR ESOPHAGEAL CANCER: A PROSPECTIVE STUDY WITH WEEKLY MRI

Abstract

Abstract Aim To assess changes in tumor volume during neoadjuvant chemoradiotherapy (nCRT) for esophageal cancer with weekly MRI. Background & Methods Neoadjuvant chemoradiotherapy (nCRT) for esophageal cancer can cause tumor regression, however data on the magnitude of the volumetric changes during nCRT are scarce. Tumor regression can induce changes in the thoracic anatomy, with smaller target volumes and displacement of organs at risk (OARs) in close proximity to the tumor target as a result. Adaptation of the radiotherapy treatment plan according to volumetric changes during treatment might reduce dose to the OARs while maintaining adequate target coverage. In the current study patients with histologically proven esophageal cancer undergoing nCRT for esophageal cancer underwent 6 MRI scans: 1 scan prior to nCRT and 5 weekly scans during treatment. Tumors were delineated on T2 weighted images by two gastrointestinal radiation oncologists and volumetric changes were assessed. Results A total of 164 MRI scans of 28 patients were included. The mean tumor volume at baseline was 45ml (SD ± 23ml). Tumor volume regression started after the first week of nCRT and appeared to be a linear process with significant declines in tumor volume every subsequent week (p-values <0.05). The mean relative volume regression was 25% (SD ±15) between baseline and the fifth week of treatment (Figure 1.) Conclusion This study shows a significant linear decrease in tumor volume after the first week of nCRT for esophageal cancer on weekly MRI. These findings suggest the possible benefit of radiotherapy plan adaptations during nCRT.