RESUMEN

Objective To compare the setup accuracies of the surface-guided radiation therapy for nasopharyngeal carcinoma based on volume rendering technique(VRT)reference surface and digital imaging and communications in medicine(DICOM)reference surface.Methods Twenty patients with nasopharyngeal carcinoma who received radiotherapy using the customized AccuCushion with a thermoplastic fixation mask were selected.After the first cone beam CT(CBCT)-based image-guided radiotherapy of each patient was completed,the thermoplastic mask was removed to obtain the VRT reference surface based on optical surface monitoring system(OSMS),during which the patient position was maintained through instructions;the DICOM reference surface was got based on the body surface contour data extracted from the patient's localized CT images.After the completion of the 5th,10th,and 15th CBCT image-guided radiotherapy treatments,the patients'6 dimensions of setup errors were measured based on the 2 reference surfaces,respectively.Dimensional correlation analyses were carried out on the setup errors measured based on the 2 reference surfaces separately using Python's Stats tool to test the independence between the setup errors in each dimension.After independence test,Wilcoxon rank sum test was performed on the data of the setup errors based on each dimension measured with the 2 reference surfaces.Results The two sets of setup errors were independent of each other in all dimensions.The errors based on VRT reference surface were lower than those based on DICOM reference surface in 6 dimensions,while the difference between the 6-D errors of the two groups did not gradually become significant as the treatment progressed.Conclusion In the SGRT of nasopharyngeal carcinoma using a customized cushion combined with a thermoplastic mask,the setup accuracy and consistency based on VRT reference surface are both higher than those based on DICOM reference surface.