A comparative analysis of setup accuracy between 6D and 3D treatment couches in radiotherapy for lung cancer with brain metastases

To evaluate the accuracy of six-dimensional (6D) treatment couches in minimizing setup errors compared with three-dimensional (3D) treatment couches during radiotherapy for lung cancer patients with brain metastases. A retrospective analysis was conducted on 40 lung cancer patients with brain metastases who received stereotactic radiotherapy (SRS/SRT) for brain metastases. The cohort was divided into two groups based on the availability of treatment units at the time of planning: 20 patients were treated using a 3D couch, and 20 patients with a 6D couch. Daily cone-beam computed tomography (CBCT) registration was used to measure residual setup errors in the x , y , and z axes at two key cranial anatomical landmarks, specifically the internal acoustic meatus (IAM) and crista galli (CG), for both groups. The Shapiro-Wilk test was applied to assess the normality of the data, and the Mann-Whitney U- test was performed to determine statistical differences between the two groups, with Bonferroni correction for multiple comparisons. Baseline data indicated that the two groups were well-balanced in terms of gender, age, and distribution of pathological types, number of brain metastases, maximum metastases volume, and relative distance between metastases and isocenter ( P >0.05). Setup error data in all directions (IAM_ x / y / z , CG_ x / y / z ) did not follow a normal distribution ( P <0.05). The Mann-Whitney U- test revealed that setup errors in the 6D group were significantly smaller than those in the 3D group across all directions (IAM_ x / y / z , CG_ x / y / z ) (all P <0.001). The mean error reduction exceeded 1 mm in all directions, with the most significant difference observed in the CG_X direction: 2.2 (1.3, 3.3) mm in the 3D group versus 0.3 (0.2, 0.5) mm in the 6D group, representing a difference of 1.9 mm. The six-dimensional (6D) treatment couch effectively minimizes residual setup errors, especially rotational ones, in radiotherapy for lung cancer patients with brain metastases