| [Objectives] Using 4D-CT and its image reconstruction technology, to determine the internal target volume(ITV) in radiotherapy of lung cancer, compared with the conventional 3D-CT technology,and to deternmine its geometric and dosimetric advantages, and to explore the clinical significance of its application in lung cancer radiotherapy.[Methods] Twenty cases with peripheral lung cancer underwent big bore axial 3D-CT scans first,and then 4D-CT simulation scan of the thorax in the condition of natural breathing,4D-CT pictures were comprised of CT images of 10 respiratory phases, then we used image reconstruction technology to obtain average intensity projection pictures.GTV3D and organs at risk were delineated on the images of conventional 3D-CT pictures and GTV contours were defined as GTV3D. IGTV4D was delineated manually on every sequence’s image of 4D-CT, and then the images of 10 breathing phase were saved at the images of 20% sequence, while its organs at risk were delineated in 20% sequence, IGTVAIP and its organs at risk were obtained in AIP-CT pictures. Three plans’s clinical target volume (CTV), were defined as isotropic enlargement of 0.8 cm on account of GTV,and then PTV3D was obtained by adding 0.8cm in left and right,anterior and posterior direction,1.5cm in superior and inferior direction,PTV4D and PTVAIP were obtained by adding 0.5cm on account of CTV,in order to contain setup margin.Three treatment plans were prepared for each patient, the dose and irradiating fields of the three plan were identical. The difference of geometric and dosimetric of target and organs at risk in the three plans were contrasted and analysed.[Results] The average volume of GTV3D, IGTV4D and IGTVAIP are 15.40±13.32 cm3,21.76±19.30cm3 and 16.26±12.81cm3, respectively,GTV3D size is smaller than that of IGTV4D (P=0.01), IGTV4D size is larger than that of IGTVAIP (P=0.03), there is not a significant difference between GTV3D and IGTVAIp (P=0.21). The average volume of PTV3D, PTV4D and PTVAIp is 187.25±71.21cm3,139.60±67.45cm3 and 119.64±50.06 cm3, respectively, PTV4D size is smaller than that of PTV3D (P=0.00),PTVAIP size is smaller than that of PTV3D (P=0.00), PTV4D size is larger than that of PTVAIP (P=0.01).The maximum, minimum, and average doses of the target are all over 50 Gy in three different plans, but changes in dosimetry haven’t significant statistically difference.Whole lung V5, V10, V20, V30 in 3Dplan were higher than that of in 4Dplan and AIPplan, differences are significant (P< 0.05),and there isn’t significant difference between 4Dplan and AIPplan (P>0.05),except V10(P=0.01). The mean dose of whole lung showes that 3Dplan is larger than than of 4Dplan (P=0.00), and3Dplan is larger than than of AIPplan (P=0.00), there isn’t significant difference between 4Dplan and AIPplan (P=0.05). The middle and lower lung’s move is bigger than that of upper lung.The heart,spinal cord, esophagus in 3Dplan are larger than that of 4Dplan and AIPplan, while the dose of 4Dplan were slightly lager than that of AIPplan.[Conclusions] 4Dplan based on the technology of 4D-CT can determine tumor target more accurately, ensuring that gross tumor volume(GTV) coverages the tumor,at the same time,planning target volume(PTV) is reduced, and the dose and volume of normal tissue can be reduced too. AIP plan can achieve the results which are similar to 4D plan, and further reduce planning target volume, and protect the normal tissues,both are better than the 3Dplan.If we cannot use 4D-CT images or consider that tumor target delineation is relatively cumbersome, delineating target contour and designing the radiation therapy plan on the images of AIP-CT may be a good method. |
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