A comparative study of GTV displacements of primary thoracic esophageal carcinoma based on repeated 4DCT scans during radiotherapy

Abstract

Objective To investigate the target volume displacements of primary thoracic esophageal carcinoma (TEC) based on repeated enhanced four-dimensional computed tomography (4DCT) scans during fractionated radiotherapy.Methods Twenty-nine patients with TEC underwent enhanced 4DCT before and in the 10th,20th,and 30th fractions of radiotherapy to delineate the gross tumor volumes (GTVs) and internal gross tumor volumes (IGTVs) in all phases.The GTV displacements of upper,middle,or lower TEC in three-dimensional directions in each time of 4DCT were compared,and the GTV displacements of upper,middle,or lower TEC in the same direction in all 4DCT scans were also compared.The changes in the centroid positions and volumes of IGTV during radiotherapy were determined.Results For the patients with middle TEC,significant differences were found between the GTV displacements in leftright (LR) direction,anterior-posterior (AP) direction,and superor-inferior (SI) direction when 4DCT was performed before or in the 20th fraction of radiotherapy (P =0.000-0.016),and significant differences were found between the GTV displacements in SI direction and LR and AP directions when 4DCT was performed in the 10th fraction of radiotherapy (P =0.000-0.006).For the patients with lower TEC,there were significant differences between the GTV displacements in SI direction and AP direction when 4DCT was performed before or in the 10th or 20th fraction of radiotherapy (P =0.004-0.013).There were no significant differences between the GTV displacements in the same direction in all 4DCT scans (P =0.102-0.823).There were no significant changes in the centroid positions of IGTV during radiotherapy (P =0.6 8 9-0.999),and the most significant decreases in IGTV volumes were seen in the 20th fraction of radiotherapy (P =0.012-0.029).Conclusions Under free breathing,the GTV displacement of upper,middle,or lower TEC in the same direction shows no significant changes in different 4DCT scans during radiotherapy;the IGTV volumes decrease significantly in the 20th fraction of radiotherapy,but there are no significant changes in the centroid positions of IGTV during radiotherapy. Key words: Esophageal neoplasm/ radiotherapy; Tomography, X-ray computed, four-dimensional; Gross tumor volume; Intrafraction target displacement