Dosimetric Effects Of Target Volume When Repeat CT Imaging And Replanning During The Course Of Three-dimensional Conformal Radiation Therapy In Esophageal Cancer

Purpose: Many patients with esophageal cancer have tumor shrinkage and/or weight loss during the course of radiotherapy. We conducted this study to determine the dosimetric effects of repeat computed tomography (CT) imaging and replanning during the course of three-dimensional conformal radiotherapy on both normal tissues and target volumes. To approach the influence to the implementation of radiation therapy by these changes.Method: 14 cases of patients with unresectable esophageal cancer were enrolled in this study to accept full course of conformal radiotherapy. CT scans were acquired after the tenth and twentieth fractions during radiotherapy. New target (GTV and PTV) were drawn and replanned on repeat 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 repeat 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 14 patients, 5 patients treated with concurrent chemotherapy and 9 patients treated with radiotherapy only. 13 patients completed the radiotherapy of a total dose of 60 to 70Gy.1 patient quit treatment after a dose of 40Gy. When replanning vs not replanning was compared, the without replanning demonstrated reduced doses to target volumes and increased doses to critical structures. During the tenth to twentieth fractions, the doses to 95% (D95)of the planning target volumes(PTV) were reduced in 85.7%(12/14) patients, by 0.07-3.84Gy(P=0.035);the maximum dose of cord(Dmax) were increased, but were not statistically significant. The mean dose of left and right lung (MLD) were no change in all patient. During twentieth to end, the D95 of PTV were reduced in 61.5%(8/13) patients, but were not statistically significant(P=0.221);and the Dmax of cord were increased in 76.9%(10/13) patients, by 0.68-5.29Gy(P=0.006);and the MLD of left lung were increased in 69.2%(9/13) patients, but were not statistically significant(P=0.064); and the MLD of right lung were increased in 92.3%(12/13) patients, by 0.01-3.8Gy(P=0.006).Conclusion: There were obvious changes in target (GTV and PTV) during fractional 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.