Analysis on setup errors of volumetric modulated arc therapy in pelvic tumors based on X-ray volumetric images / 医疗卫生装备

ABSTRACT

Objective To acquire setup error with X-ray volumetric images (XVI) technique during volumetric modulated arc therapy (VMAT) of pelvic tumors in order to provide guidance for the doctor to determine the interval between clinical target volume (CTV) and planning target volume (PTV).~ Totally 20 pelvic tumor patients accepting radiation oncology underwent CBCT scan before the first treatment,and auto registration was executed between CBCT images and planning CT images to determine the setup errors at X,Y and Z directions.Then the patients experienced another CBCT scan to obtain residual setup errors,VMAT was carried out after auto on-line correction by the treatment couch,and the third CBCT scan was performed after the treatment.Totally three times of CBCT scans were implemented every week hereafter.The setup errors were analyzed before and after the treatment,and the target volume margin (MPTV) was calculated accordingly.Results The setup errors at X,Y and Z directions were significantly decreased after correction.The values of MPTV at X,Y and Z directions before correction were 3.89,6.20 and 5.24 mm respectively,and the ones after correction were 1.42,2.42 and 2.40 mm respectively.The decreased values of MPTV were between 2.47 and 3.78 mm,which showed the most significant trend at Y direction.Conclusion VMAT of pelvic tumors based on XVI contributes to decreasing the setup errors and enhancing treatment quality.