PURPOSE: To compare two registration methods in the CBCT guided radiotherapy for @entity2622 , analyze the setup errors and registration methods, determine the margin required for clinical target volume(CTV) extending to planning target volume( @entity343 ). METHODS: Twenty @entity1 with @entity2622 were enrolled. All @entity1 were underwent CT simulation in the supine position. Transfering the CT images to the treatment planning system and defining the CTV, @entity343 and the organs at risk (OAR), then transmit them to the XVI workshop. CBCT scans were performed before radiotherapy and registered to planning CT images according to bone and gray value registration methods. Compared two methods and obtain left-right(X), superior-inferior(Y), anterior-posterior (Z) setup errors, the margin required for CTV to @entity343 were calculated. RESULTS: Setup errors were unavoidable in postoperative @entity2622 irradiation. The setup errors measured by method of bone (systemic    random) on X(1eft.right),Y(superior.inferior),Z(anterior.posterior) directions were(0.24  3.62),(0.77  5.05) and (0.13  3.89)mm, respectively, the setup errors measured by method of grey (systemic    random) on X(1eft-right), Y(superior-inferior), Z(anterior-posterior) directions were(0.31  3.93), (0.85  5.16) and (0.21  4.12)mm, respectively.The spatial distributions of setup error was maximum in Y direction. The margins were 4 mm in @entity1112 , 6 mm in Y axis, 4 mm in Z axis respectively.These two registration methods were similar and highly recommended. CONCLUSION: Both bone and grey registration methods could offer an accurate setup error. The influence of setup errors of a @entity343 margin would be suggested by 4mm, 4mm and 6mm on X, Y and Z directions for postoperative radiotherapy for @entity2622 .

SU-E-J-88: The Study of Setup Error Measured by CBCT in Postoperative Radiotherapy for XXXX .

@entity1 :: ('9606', 'Species') :: ['patients'] @entity1112 :: ('MESH:D040181', 'Disease') :: ['X axis'] @entity2622 :: ('MESH:D002583', 'Disease') :: ['cervical carcinoma'] @entity343 :: ('187978', 'Species') :: ['PTV']
@entity2622 :: (MESH:D002583,Disease) :: ['Cervical Carcinoma']
