Uncertainty Of Target Volume And Organ At Risk During Fractional Radiotherapy In Esophageal Cancer

Purpose:To investigate the changes of target and organ at risk surrounded during fractional radiotherapy in esophageal cancer.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 every ten fractions during radiotherapy.New GTV and PTV were drawn on repeat CT scan,to evaluate the volume changes of GTV and PTV.Then copy the pretreatment planning to the repeat CT scan.To evaluate the coincidence extent between the new target and the pretreatment planning.Results:The overall trend of the GTV volume changes was decreasing during fractional radiotherapy.However,in 14 patients,the volume of GTV increase in 5 patients(35.7%)at 10 fraction.Changes in the range of 0.4 cm~3～11.32 cm~3,coresponding the relative size of the percentage of the initial volume of GTV 2.0%～37.7%.The volume of PTV consisted by 95%isodose curve were changed during fractional radiotherapy,pretreatment 97.8±1.53%,10 fraction 91.95±5.25%,20 fraction 94.27±4.23%and 30 fraction 94.03±6.45 %.The volume of PTV consisted by 95%isodose curve decrease below 95 %in several cases,6 cases in 10 fractions,5 cases in 20 fractions and 4 cases in 30 fractions.The radiation dose and radiation volume of organ at risk were changed during fractional radiotherapy,however the changes did not reach statistical significance compared to pretreatment planning.Conclusion:There were obvious changes in target(GTV and PTV)during fractional radiotherapy,which result in uncertainties during implementation of radiation therapy It needs to deal with these uncertainties through quality assurance(QA)and quality control(QC)to guarantee the normal operation of radiotherapy,and to introduce new radiation technology to resolve problems.