Analysis of placement error of stereotactic body radiotherapy in the treatment of non-small cell lung cancer / 中国医师进修杂志

ABSTRACT

Objective:To study the accuracy and positioning error of image guidance during the treatment of body stereotactic radiotherapy (SBRT) in patients with non-small cell lung cancer (NSCLC) by cone beam CT (CBCT) of VERO system.Methods:The clinical data of 80 NSCLC patients from January 2017 to December 2018 in Lishui People′s Hospital of Zhejiang Province were retrospectively analyzed. The maximum density projection and average density projection were reconstructed by four dimensional cone beam CT (4DCBCT), and internal target volume (ITV) was obtained by mapping the tumor profile. The translational and rotating tumor positioning errors were determined by comparing the manual ITV registration with the motion-fuzzy tumor on the CBCT. At the same time, correction was completed by the robot positioning bed and circular rotation. After correction, the CBCT was verified to evaluate the residual error.Results:The initial set average three dimensional vector displacement was significantly greater than the six dimensional automatic calibration displacement (6.8 ± 2.1) mm vs. (1.5 ± 0.5) mm, and there was statistical difference ( P<0.01); 94.0% (425/452) of the rotation error was ≤ 3°. If there was no image guidance, the stereo positioning based on ExacTrac required 6.6 mm in the left-right direction, 9.8 mm in the up-down direction, and 6.5 mm in the front-back direction. After six dimensional correction of residual errors, the safety margins in three directions were reduced to 3.0, 3.2, and 3.1 mm, respectively. Conclusions:Online image guidance using ITV-CBCT matching technology and the automatic six dimensional correction of the VERO system can reduce the positioning error in SBRT treatment of NSCLC patients and improve the accuracy of tumor positioning.