RESUMEN
Objective To analyze the setup errors of external?beam and intracavitary radiotherapy for cervical cancer based on the data of cone?beam computed tomography ( CBCT) , and to provide a basis for clinical practice. Methods Sixty patients with stage ⅡA?ⅢB cervical cancer who were admitted to our hospital and underwent external?beam and intracavitary radiotherapy from March to June, 2015 were enrolled as subjects. Sixty patients with stage ⅡA?ⅢB cervical cancer undergoing conventional external?beam radiotherapy within the same period were also enrolled. The CBCT?based setup errors, containing setup errors in x, y, and z directions and three?dimensional vector deviation, in the initial treatment were obtained from each patient. Comparison of errors between the two treatment approaches was made by independent?samples t test. Results Fitting the data to a linear model revealed that the setup errors in x, y, and z directions increased with the increase in the distance between the position reference point and the center point of the target volume. External?beam radiation combined with intracavitary radiation had significantly reduced setup errors in x, y, and z directions than the conventional external?beam radiation ( 0.13± 0?12 vs. 0.31± 0?24, P=0?000;0.23±0?18 vs. 0.47±0?36, P=0?001;0.18±0?11 vs. 0.27±0?18, P=0?001). Conclusions In order to reduce the setup errors, CT scan needs not only a reference marker as close as possible to the center of the tumor, but also a reliable and accurate approach for postural fixation.