The Preliminary Study Of The Internal Margin Of The Gross Tumor Volume Of Thoracic Esophageal Cancer

Purpose: To approach the displacement of the gross tumor volume (IGTV) of thoracic esophageal cancer in the calm sate of end-inspiratory and end-expiratory, in order to determine the internal margin of the gross tumor volume (IGTV), and avoid leaking target volume or the scope of target volume was too large during the radiation therapy.Methods and materials: 22 patients with thoracic esophageal cancer in our hospital were collected, who were not able to surgery and withstand radiotherapy, by 16-slice spiral CT scanning obtained the calm state of end-inspiratory and end-expiratory CT images, after reconstruction, the two-phase CT images were fused, then measured the displacement (X-axis direction) of the right sector, the left border, (Z-axis direction): The former sector after sector, (Y-axis direction): the upper bound of the first direction, that is, the lower bound feet toward the direction of volume change, and the volume change of tumor target volume, and analyzed whether these changes had something to do with the tidal volume, the location and length of the target volume, which helped to determine the internal margin of the gross tumor volume (IGTV).Results: the tidal volume average was 463.6ml. The average volume of GTV: end-inspiratory was 33.3ml, end-expiratory w?as 33.5ml (not significant, P = 0.973 > 0.05). According to Stroom, etc. and the target area covered by the possibility of using DVH analysis, pointing out that to ensure at least 95% of the dose with 99% of the volume of CTV, CTV to PTV boundary should be at least (2Σ+0.7σ), while the PTV includes ITV and SM; ITV includes CTV and IM, but this study IGTV side of the expansion areas, namely, IGTV = GTV+ IM; therefore ensure that at least 95% of the dose with 99% of the volume of GTV, GTV to IGTV boundary should be at least MIGTV = (2Σ+0.7σ) ,The internal margin of the gross tumor volume: (X-axis direction):the right sector was 3.09mm, the left border was 4.08mm, (Z-axis direction):the anterior border was 3.96mm, the post-border was 2.83mm, (Y-axis direction): the upper bound(the head direction )was 7.31mm, the lower bound(the feet direction) was 10.16mm. The motion of GTV had no significant correlation with the tidal volume of patients and the length of tumor, but related to the tumor location, the displacement of the lower thoracic and the middle thoracic target volume in the direction of the heads ,feet ,former and left were significantly different (P<0.05), no significant difference in the other directions (P>0.05).Conclusions: Due to respiratory movement and organs'movement, the displacement of the tumor target volume (GTV) were different in all directions, therefore, it was recommended the expansion of the planning target volume (PTV) in the clinical radiation treatment should take the displacement of the tumor target volume caused by respiratory movement and organs'movement during each radiotherapy into account,in order to improve the efficacy of radiation therapy.