ABSTRACT
Objective To analyzed the effects of the positioning errors and weight variability of the head and neck cancer patients with intensity modulated radiation therapy (IMRT),or volumetric modulated arctherapy (VMAT) based on the kilovoltage cone-beam computed tomography (kV-CBCT).Methods CBCT images of 102 patients with head and neck cancer patients receiving IMRT or VMAT were screened by CBCT once a week for consecutively 6 weeks.The positioning errors were measured by comparing CBCT and planning CT in left-right (LR),anterior-posterior (AP) and cranio-caudal (CC) directions.Meanwhile,the weight of patients were measured every week.Results The positioning errors were (0.011 5±0.125 3) cm,(-0.017 6±0.123 3) cm and (-0.014 1±0.156 7) cm in LR,AP and CC directions,respectively.The mean systematic errors were all less than 0.02 cm in three axial directions,while the mean random errors were all within 0.2 cm.There was no statistically significant difference was observed among the setup errors in all three axial directions according to different week.Though the body weight of patients continued to drop during the radiation by with the mean weight loss of 3.5 kg and had a negative correlation with treatment course.Bivariate correlation analysis showed just the positioning errors in CC direction were significantly correlated with body weights loss.Conclusion There is no statistical relationship with in position errors of the patients with their treatment course,and the body weight loss seemed to influence the position errors in CC direction.
ABSTRACT
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.