Accuracy Treatments With Frameless Stereotactic Radiosurgery

Radiosurgery treatments using invasive cranial frame-based immobilization systems have amply demonstrated their accuracy. Modern treatment techniques tend to replace fixed immobilization systems (uncomfortable for patients) with new Frameless immobilization systems. We aimed to demonstrate the accuracy of the treatment using a Frameless system (Fraxión model) and a robotic table with 6 degrees of freedom (Hexapod table model). We compared 14 patients who were treated with single fraction radiosurgery for brain metastases. Seven of them using frame-based immobilization system (Leksell model) and 7 using a thermoplastic mask, vacuum mattress, cervical and oral fixation (Fraxion model). In each of the 14 patients a robotic table with 6 degrees of freedom (Hexapod model) was used. In all cases a pre and post cone-beam CT were performed, in order to compare both translational and rotational intrafraction motion. Translational axis X (lateral), Y (longitudinal) and Z (vertical); and rotational: X angle or Pitch (right and left rotation), Y angle or Yaw (anteroposterior rotation axis) and Z angle or Roll (superior-inferior rotation axis). The treatment technique we used was Volumetric Modulated Arc-therapy (VMAT) with a single isocenter and a minimum of 5 non-coplanar arcs, using the Monaco 5 planner (Monte Carlo algorithm). Six MV photons supplied by a LINAC with multileaf collimator of 0.4 cm sheets at isocenter were used. The analysis of the images obtained from 28 cone-beams CT, 14 of each immobilization system, offers intrafraction differences(mean and standard deviation) of less than 1mm in translational motion ( X, Y, Z) and less than 0.5º in rotational motion. It is slightly smaller with frame-based immobilizer (Leksell) as shown in Table 1 below.Abstract 2187; Table 1.Lateral (X mm)Longitudinal (Y mm)Vertical(Z mm)Pitch (X°)Yaw(Y°)Roll(Z°)LeksellAverage Stand.Dev0.06 0.040.04 0.030.03 0.030.35 0.320.10 0.090.20 0.15FraxionAverage Stand.Dev0.08 0.060.09 0.090.12 0.090.43 0.330.40 0.350.41 0.32 Open table in a new tab The robotic table with 6 degrees of freedom (Hexapod) allows for repositioning with pinpoint accuracy. The Frameless immobilization system we used (Fraxion model) confers superponible intrafraction stability as the classic Frame-based systems, so that it is not necessary to extend the PTV margin. The Frameless immobilization system (Fraxion model) is much more comfortable for the patient and easier to integrate into the radiation therapy department workflow, involving less service staff than the classics systems.