Dosimetric Effect Studies Of Tumor And Organs At Risk For The Upper Dilation Part Of Thoracic Esophageal Cancer During The Course Of Radiotherapy

[Objective]When sketching the esophageal target,we usually expand up and down 3 cm respectively, in consideration of the skip metastases of the esophageal mucosa Chinese patients often saw doctors later, the partial patients’ tumor was found so late that the upper part of the esophageal swelling was dilated obviously, and the lesions in the upper part of the esophagus would be varying degrees of effusion, product gas and expansion. According to 8mm putting to CTV, CTV considering setup errors putting 8-10mm to GTV, the target area will increase significantly. Many patients with esophageal cancer have tumor shrinkage and dilatation reduce during the course of radiotherapy. If the design of the target in accordance with the beginning of radiotherapy continues,it will result in additional illumination such as lung, spinal cord and other normal tissues, and also will have an impact on esophageal tumor dose. We conducted this study to determine the dosimetric effects of the upper dilation part of thoracic esophageal cancer during the course of radiotherapy on both normal tissues and target volumes. To approach the influence to the implementation of radiation therapy by these changes.[Methods]In this study we retrospectively collected 10 cases of patients with unresectable esophageal cancer,who were enrolled in this study to accept full course of conformal radiotherapy in Shandong Cancer Hospital since December 2012 to December 2014. Case selection criteria:1. Accompanied by significant thoracic esophageal obstruction, the upper part of the esophageal swelling was dilated obviously.2. The expansive part significantly reduced due to tumor shrinkage. According to the new CT scans during the patients resetting,New target (GTV and PTV) were drawn and replanned on new CT scan(new plan is only for research, rather than for treatment).we evaluated the volume changes of GTV and PTV. Then copy the pretreatment planning to the new CT scan. To evaluate the dose and/or volume change between the new target and the pretreatment planning on both normal tissues and target Volumes.[Results]In 10 patients,8 patients treated with concurrent chemotherapy and 2 patients treated with radiotherapy only.10 patients all completed the radiotherapy of a total dose of 60 to 70Gy. When replanning vs not replanning was compared, the without replanning demonstrated reduced doses to target volumes and increased doses to critical structures. The maximum dose of spinal cord (Dmax) were increased, were statistically significant. The mean dose of both lung (MLD) were also statistically significant changing in all patient. [Conclusions]There were obvious changes in target (GTV and PTV) of the upper dilation part of thoracic esophageal cancer during the course of radiotherapy,which result in uncertainties during implementation of radiation therapy. Repeat CT imaging and replanning is essential to identify dosimetric changes and to ensure adequate doses to target volumes and safe doses to normal tissues. Future prospective studies with larger sample sizes will help to determine criteria for repeat CT imaging and replanning, or new radiation technology is introduced to resolve this problems.