Feasibility and advantages of markerless positioning guided by SGRT in non-surface tumor radiotherapy: focus on esophageal cancer

Our institute uses tattoos and skin markers in radiotherapy positioning, but permanent tattoos or loss of skin markers may negatively affect treatment. To evaluate markerless positioning in non-surface tumor applications, we use esophageal cancer as an entry point. We examined 52 esophageal cancer patients' treatment records retrospectively. A total of 26 patients were positioned with traditional tattoos, skin markers, and laser systems (group A). The remaining 26 patients used surface-guided radiotherapy (SGRT) only for markerless positioning (group B). Before treatment, all patients had cone-beam computed tomography (CBCT) scanning, and six degrees of freedom (6DOF) shifts were recorded. The absolute setup errors for the CBCT were compared between the two groups. Furthermore, group B's positioning time and total treatment time were recorded to assess the positioning efficiency. 627 and 637 treatment fractions of groups A and B were compared and analyzed, respectively. The results demonstrated that group B's median shift magnitude was superior to group A's in the lateral (0.11 cm vs 0.18 cm, p < 0.001), longitudinal (0.14 cm vs 0.25 cm, p < 0.001), pitch (0.60 deg vs 1.30 deg, p < 0.001), and roll (0.50 deg vs 0.8 deg, p < 0.001) directions. In addition, the mean (median) positioning time in group B was 38.45 (35) seconds, and the mean (median) total treatment time was 486.42 (480) seconds. Markerless positioning using SGRT for esophageal cancer is accurate and efficient, providing a safe alternative for patients avoiding tattoos or skin markers.