RESUMEN
Objective To evaluate the effect of popliteal fossa fixed method to reduce the setup errors in patients with postoperative cervical carcinoma by CBCT of TrueBeam Linear accelerator.Methods 30 cases of postoperative cervical cancer patients were randomly divided into two groups,group A with popliteal fossa fixed method by trapezoidal fixation,group B with traditional vacuum pad fixation.CBCT was used to record both setup errors and rotational errors,Stroom extension formula was used to calculate the PTV expansion value coming from the two different fixation methods.Results There was significant difference in setup errors between group A and group B.The setup errors in the left-right direction (X),cranial-caudal direction (Y) and anterior-posterior direction (Z) were (0.19±0.14) cm,(0.17±0.12) cm and (0.13±0.11) cm in group A,respectively.On the contrary,the setup errors in X,Y and Z were (0.24±0.19) cm,(0.25±0.21) cm and (0.22±0.18) cm in group B,respectively.The rotational errors were 0.05°±0.02° in group A,comparing with 0.5°±0.21° in group B (P =0.00).The PTV expanded margin in group A was 0.56 cm in X direction,0.51 cm in Y direction,0.40 cm in Z direction,in comparing with 0.73 cm,0.78 cm and 0.67 cm in group B,respectively.Group A remarkably reduced the PTV,pelvis,small intestine,bladder and rectum irradiated volumes [(1 167±271) mm3 vs (1 379±297) mm3,(84±12) mm3 vs (130±17) mm3,(81±51) mm3 vs (117±64)mm3,(62±40) mm3 vs (75±47) mm3,(21±16) mm3 vs (31±21) mm3].Conclusion Popliteal fossa fixed method can reduce setup errors and improve the stability of positioning,more suitable in precise radiotherapy for postoperative cervical cancer patients,which has the value of further validation.