Abstract: Objective The aim of this study was to investigate the dosimetric advantages of Gating in the treatment of primary hepatic cancer with large segmentation.Methods A retrospective analysis of 10 patients with primary liver cancer from August 2017 to November 2018 after interventional therapy was performed using three consecutive phases of end-tidal phase to achieve patient-controlled large-segment radiotherapy.Ten patients underwent 4DCT localization scan,and 10 respiratory phase sequences were reconstructed by respiratory wave-form,and the images were transmitted to the MIM6.7.6 workstation.In the MIM workstation,full-time phase maximum density projection(MIP-10),full-time phase average density projection(Mean-10),end-expiration 3 phase maximum density projection(MIP-3)and end-expiration 3 phase average density projection(Mean-3)were generated respectively,where MIP was used for target delineation and Mean for dose calculation.The radiotherapy doctor delineated IGTV-10 and IGTV-3 on the MIM workstation,and released CTV-10,CTV-3,PTV-10 and PTV-3 to compare the volume differences of the target area.After the target area was drawn,the image was transmitted from the MIM workstation to the Eclipse treatment planning system,and the full-time phase plan(Plan-10)with the same conditions and three consecutive phase-phase gating plans(Plan-3)were prepared.The prescriptive dosage was given at 50 Gy/10 f/2weeks.Comparing the HI and CI of the target area,the comparison of organs at risk included: the average dose of liver Dmean,the irradiation volume of liver less than 15Gy,the Dmax of small intestine,the Dmax of colon,the Dmax of stomach,the average dose of the kidney Dmean,the heart Dmax,and the spinal cord Dmax.Results The volume of the target area delineated at the end of expiratory phase was less than that of the target area outlined by the full-time phase in IGTV,CTV and PTV,and the difference was statistically significant(P＜0.05).In the two groups of seven field coplanar lage-segment radiotherapy plans,the 3-phase respiratory gating plan significantly reduced the dose of the organs at risk,and the difference was statistically significant(P＜0.05).At the same time,there was no statistically difference in the HI and CI between of the two groups(P＞0.05).Conclusion The gated target area delineation and planning design of the three consecutive phases of end-tidal phase reduce the volume of IGTV,CTV and PTV target regions compared with the selection of full-time phase,and have obvious advantages in the planned dosimetry.The irradiation dose that threatens the organs is worthy of being promoted and applied in the large-scale radiotherapy of liver cancer.

Key words: Hepatocellular carcinoma, 4DCT, Respiratory gating, Large segmenting radiotherapy, Dosimetry