| Objective: This study was designed to define individualized IGTV4D and IGTVgating using 4D-CT, compare target volumes and dose distribution among 3D plans, 4D plans, and respiratory gating plans,evaluate the clinical significance impact of 4D-CT imaging on advanced non-small cell lung cancer(NSCLC).Methods: 15 patients with advanced non-small cell lung cancer were selected. Everybody reseived unenhanced conventional CT scan, as well as retrospective 4D-CT scan under quier respiration. Then their conventional CT scan images and 10 sequence CT scan images of different breathing phase were abtained. GTV and normal organs were delineated on the image of conventional CT, GTV contours was defined as GTV3D. IGTV was delineated manually on every sequence's image of 4D-CT, which was defined as to envelope the respiratory motion of the gross tumor volume. IGTV from the 10 breathing phase CT scan images was save at the image of 20% sequence, which was knowen as IGTV4D, and outlines of normal organs were delineated on the 20% sequence too. IGTV from the images of 40%, 50% and 60% breathing phases was saved at the CT scan image of 50% sequence and named IGTVgating, outlines of normal organs were also delineated on the 50% sequence.Three treatment plans were prepared for each patient on account of three different PTV respectively, PTV3D, PTV4D and PTVgating. PTV3D was derived from conventional CT scan, its margin is defined as an isotropic enlargement of 1.5 cm on account of GTV in order to account for microscopic extension, respiration-induced mobility and set-up inaccuracies, but a 2.0 cm enlargement was adopt at the derection of cranial and caudal for tumors in lower lobe of lung. PTV4D is consisted of the volume encompassing all 10 IGTVs (i.e. all respiration-induced mobility) plus an isotropic margin of 1.0 cm for microscopic extension and positioning error; PTVgating include IGTVgating adding an isotropic margin of 1.0 cm for microscopic extension and positioning error.The dose and irradiating fields of the three plan is identical. The volumes and dose distribution of the three PTVs were compared.Result: The average volume of IGTVgating was 28.57士23.28 cm3, which was 8.43土12.42 cm3 less than IGTV4D(36.99士29.68 cm3). The average volume of PTV3D, PTV4D, PTVgating were 205.07±87.24 cm3, 156.63±85.03 cm 3 and 134.73±72.04 cm3 respectively. PTV4D is 48.45土31.23 cm3 less than PTV3D, PTVgating is 70.34土28.76 cm3 less than PTV3D and PTVgating is 21.89土32.78 cm3 less than PTV4D.Among the three PTV, PTV3D volume is largest in all 15 patients, but it missed partial target volume in 3 patients compared to PTV4D.The volume of PTV4D was larger than PTVgating, but smaller than PTV3D.Compared with PTV3D, V5, V20, V30 and the mean lung dose (MLD) of PTV4D were all reduced. V5 was reduced from 35.07士15.17% to 29.50士14.59, V20 was reduced from 16.08士5.45% to 13.29士5.08%, V30 was reduced from 12.97士4.12% to 10.72士3.98% and MLD was reduce from 1021.20士343.15cGy to 848.13士342.66cGy. Compared with PTV3D, The V5 of PTVgating was reduced from 35.07士15.17% to 28.85士14.39% meanly,V20 was reduced from 16.08士5.45% to 13.05士5.05%, V30 was reduced from 12.97士4.12% to 10.35士3.77% and MLD was reduced from 1021.20士343.15cGy to 807.00士316.18cGy.Compared with PTV4D , The V5 of PTVgating was reduced from 29.50士14.59% to 28.85士14.39% meanly,V20 was reduce from 13.29士5.08% to 13.05士5.05%, V30 was reduced from 10.72士3.98% to 10.35士3.77% and MLD was reduced from 848.13士342.66cGy to 807.00士316.18cGy.Conclusion: Compared with 3DCRT, 4D planning which on account of 4D-CT can determine the moving tumor margin more accurately and reduce the impact of respiratory movement on the target. 3D plan has a extended target and may miss part of target compared with the 4D plan. The 4D plans can ensure a optimal target relatively which can cover the whole tumor region meanwhile with a less irradiation dosage on normal tissues, then allow a higher radiation on tumor compared with 3DCRT. Respiratory gated radiotherapy can further enable smaller target volumes and more conducive to protecting the normal tissues to spare more surrounding tissues. |
