Improvement in positional accuracy with integrated surface- and X-ray imaging for intracranial stereotactic radiosurgery patients

Background and purpose Stereotactic radiosurgery (SRS) requires high positional accuracy to safely deliver large doses. This study evaluated an integrated surface- and image-guided radiotherapy (SGRT-IGRT) system by analysing (1) the agreement between thermo-optical and stereoscopic X-ray positioning, and (2) the impact of intra-fractional workflows on treatment accuracy and time. Materials and methods Data from 126 SRS patients treated with 30 Gy/3 fractions (n = 116) or 12 Gy/1 fraction (n = 10) on a Varian Truebeam STx were retrospectively analysed. Patients were positioned and monitored with Brainlab ExacTrac Dynamic, with 0.5 mm/0.5° tolerances for IGRT and 1 mm/1° for SGRT. Three workflows were investigated: (A) SGRT + IntraArc IGRT (imaging every 90° during treatment and between couch rotations); (B) SGRT + InterArc IGRT (imaging between couch rotations only); and (C) SGRT (no additional imaging after initial coplanar setup). Workflows (B) and (C) were simulated by omitting applied couch corrections. Results Median beam-on times were 5.5 min for workflow A, 5.0 min for workflow B, and 3.2 min for workflow C. The median differences between thermo-optical and stereoscopic X-ray patient positioning were ≤0.1 mm. The 3D positioning uncertainty remained within 0.5 mm (2.5th-97.5th percentile) using SGRT-IGRT. Omitting inter-arc imaging increased positional deviation ranges from 0.1-0.5 mm to 0.1–0.7 mm. Conclusion Thermo-optical and stereoscopic X-ray imaging showed good agreement within the set institutional tolerances. Inter-arc imaging increased treatment time by 2 min compared with SGRT alone but improved positioning accuracy. Intra-arc imaging added an additional small accuracy benefit at minor time cost.