Changes in Patient Marker Coordinates with High-Definition Motion Management System during Frameless Gamma Knife Radiosurgery.

Objective: The Leksell Gamma Knife (LGK) Icon™ facilitates frameless (mask-based) fixation through its high-definition motion management (HDMM) system. However, the HDMM only records the intra-fractional motion values of patient marker without specifying changes along the X, Y, and Z axes. This study investigates the coordinate shifts in patient markers using the HDMM system during frameless gamma knife radiosurgery (GKRS) in patients with meningioma and metastases.

Methods: We conducted a retrospective study of patients diagnosed with meningioma or metastases who underwent frameless GKRS using the LGK Icon™ between January and September 2023. All patients were immobilized using a Nanor thermoplastic mask (Orfit Industries, Wijnegem, Belgium) for frameless fixation. Sequential data of the patients' nose marker coordinates (X, Y, Z) were imported into the LGK system, and subsequent coordinate changes were analyzed.

Results: We evaluated patients with meningiomas (n=30) and metastases (n=30) who underwent GKRS with frameless fixation. None of the patients exhibited cognitive impairment or compliance issues. The median beam-on time was 44.2 minutes in patients with meningioma and 93.75 minutes in patients with metastases. In patients with meningioma, no significant intra-fractional displacements were found along the X (0.07±0.06 mm), Y (0.08±0.46 mm), and Z (0.08±0.04 mm) axes. However, in patients with metastases, the Y axis (0.57±0.37 mm, p<0.05) exhibited significantly greater intra-fractional displacements compared with the X axis (0.33±0.23 mm). No significant differences in intra-fractional displacement were observed between the X and Z (0.43±0.31 mm) axes or between the Y and Z axes. An analysis of movement over time revealed a significant increase in Y axis displacement after 30 minutes.

Conclusion: Y axis movement, as indicated by the HDMM, was most prominent in patients with metastases. We recommend pressing the forehead when securing a mask to minimize nose marker movement. Additionally, when creating treatment plans for managing patients with metastases using the LGK Icon™, we suggest adding a 0.5 mm margin to the Y axis.