ABSTRACT
Objective:To investigate the consistency and correlation of the respiratory synchronization tracking and fiducial marker respiratory synchronization tracking in the Cyberknife stereotactic body radiotherapy (SBRT) with the diaphragm as the tracking target.Methods:A total of 11 patients hospitalized at Union Hospital Affiliated to Tongji Medical College of Huazhong University of Science and Technology from April 2018 to November 2019 were enrolled, including 8 cases of lung cancer, 2 cases of liver cancer with lung metastasis and 1 case of colorectal cancer with lung metastasis. All enrolled cases used fiducial marker tracking plan (RT) and diaphragm contour tracking plan (DT), and then all received tumor visualization simulation tests. Bland-Altman method was used to make the consistency analysis of the offset in the visualization tests process of 2 tracking plans at each respiratory time point. The minimum tolerance distance, uncertainty and average standard deviation and maximum standard deviation in the optimal model state plans were compared between the both plans by using t test. Results:Compared with RT, the translational standard deviations of DT tracking were listed as follows: head-foot direction (0.4±2.9) mm, left-right direction (0.3±4.4) mm, anterior-posterior direction (-1.8±6.8) mm. The Bland-Altman method showed that the consistency between RT and DT was better in the head-foot and left-right directions, and worse in the anterior-posterior direction; the synchronization was only better in the head-foot direction, and worse in both the left-right and anterior-posterior directions. Results of the model quality comparison showed that the uncertainty of RT was higher than that of DT, and the difference was statistically significant [(23±6)% vs. (9±4)%, t=-5.24, P = 0.001], while the differences of the minimum tolerance distance, average standard deviation and maximum standard deviation were not statistically significant (all P>0.05). Conclusions:Patients who use respiratory synchronization Cyberknife SBRT with the diaphragm as the tracking target have better consistency and synchronization in the head-foot direction, but worse in the left-right and anterior-posterior directions. Under the corresponding marginal margin of the target area in the left-right direction, for tumors near the diaphragm that are not visible in the visual test, it is potentially feasible to use the diaphragm as a tracking target to implement respiratory synchronization SBRT. For larger motion amplitudes in the left-right and anterior-posterior directions, more caution is required.