The Comparison Of Radiotherapeutic Plans Based On Internal Target Volume Determined By Between Three Multiphase CT And Addition Of Generic Margin In Lung Cancer

Objective:Lung tumors exhibit significant motion induced by respiration during the course of radiotherapy. How to reduce its adverse impact in precise radiotherapy and methods to account for respiratory motion have become the focus of ongoing researches recently. The aim of the present study was to compare of radiotherapeutic plans based on internal target volume (ITV) determined by between multiphase CT and addition of generic margin in lung tumors, and evaluate the reliability of ITV determined by multiphase CT during conventional fractionated radiotherapy.Methods:For all ten patients with lung cancer, a helical CT scan was acquired under normal free breathing followed by two breath-hold helical CT scans taken at end-inspiration and expiration. Two kind of target volumes were delineated using two different methods. The original radiotherapeutic plans based on ITV determined by between three multiphase CT and addition of generic margin for each patient were performed, respectively. The differences of two GTVs and PTVs and irradiated doses and volume of normal lung tissue were compared. Weekly new targets were delineated on repeated CT scans, then weekly GTVs volume change and dose coverage of CTVs under two different original plannings were investigated.Results:For all ten patients, the percentage of GTV volume under normal free breathing was 116.6-228.9% (median 151.2%) compared to the IGTV volume. However, PTV3CT volume based on multiphase CT for each patient was significantly smaller than that of PTVconv based on addition of generic margin(t=6.831,P<0.001). V20 of normal lung tissue in Plan3CT and Planconv were 16.7±5.2% and 20.0±5.2%(t=7.565,P<0.001), V5 were 36.6±7.2% and 42.7±6.4%(t=7.459,P<0.001), and MLD were 1037.5±275.0cGy and 1246.8±271.0cGy(t=8.078,P<0.001), respectively. Moreover, the weekly GTV volume of all patients decreased gradually during the course of radiation treatment. Both of original Plan3CT and Planconv provided a satisfied CTV coverage weekly during conventional fractionated radiotherapy for 6-7 weeks, and the ratios of Vp were 1.028±0.021 and 1.042±0.017, respectively. Conclusions:The radiotherapeutic plan based on ITV determined by three multiphase CT can ensure weekly target coverage during conventional fractionated radiotherapy of lung cancer, and it is better than the plan based on addition of generic ITV, which can effectively reduce normal lung tissue irradiation.