Setup error analysis of image registration using various regions of interest after individualized nasopharyngeal carcinoma radiotherapy immobilization / 中国医学物理学杂志

ABSTRACT

Objective To explore the effects of image registration using various regions of interest(ROI)on the setup error for nasopharyngeal carcinoma(NPC)patients who were immobilized individually.Methods Forty-three NPC patients who required radiotherapy were enrolled.The patients were immobilized with customized plastic foam and thermoplastic mask,and CBCT verification was performed once a week.In CBCT images,ROI was divided into the whole ROI(ROIPTV)and 7 local ROI containing different cervical structures(ROIsphenoid sinus,ROIatlantoaxial,ROIneck3,ROIneck4,ROIneck5,ROIneck6,and ROIneck7),which were then used for registrations with localized CT image.The setup errors in superior-inferior(SI),left-right(LR),anterior-posterior(AP),Pitch,Roll,and Yaw directions were recorded.Results In SI direction,the setup errors within 0.3 cm accounted for 89.74%for ROIneck7,and more than 90%for the other ROI.The proportion of setup errors within 0.3 cm gradually increased with the neck upward in LR direction,and they were 76.78%,81.70%,85.26%,and above 90%for ROIneck7,ROIneck6,ROIneck5,and the other ROI,respectively.In AP direction,the proportions of setup errors within 0.3 cm were less than 90%,except for ROIatlantoaxial and ROIneck3.The setup errors of ROIsphenoid sinus,ROIatlantoaxial,ROIneck3,and ROIneck4 were significantly positively correlated with ROIPTV in SI direction,and the correlation coefficients(R)were 0.94,0.95,0.90,and 0.83,respectively.In LR direction,there were positive correlations between the setup errors of ROIatlantoaxial and ROIsphenoid sinus(R=0.95),ROIneck3 and ROIsphenoid sinus(R=0.91),ROIPTV and ROIneck3(R=0.91).The setup errors of ROIPTV in AP direction were positively correlated with ROIatlantoaxial vertebrae and ROIneck3(R=0.88,0.90).The margins of all ROIs ranged from 0.38 cm to 1.01 cm.The extension of ROIneck6 and ROIneck7 in AP direction exceeded 0.9 cm,and the extension of ROIneck7 reached 0.95 cm in SI direction.Conclusion ROIPTV and ROIsphenoid sinus,ROIatlantoaxial,ROIneck3 are significantly correlated in SI,LR,and AP directions.The setup error of nasopharyngeal carcinoma patients gradually increases with the neck down.The nasopharyngeal and cervical regions need to be expanded in segments when patients are immobilized individually.