Validation of Catalyst+ HD System Under Varying Postural, Couch Angle, and Isocenter Conditions in Intracranial Stereotactic Irradiation.

Background/aim: This study assessed the positional detection accuracy of the Catalyst⁺ HD system for intracranial stereotactic irradiation (STI) under clinically relevant conditions, including variations in head posture, isocenter position, and couch angle.

Materials and methods: An anthropomorphic head phantom was used to simulate three head postures, chin-up, neutral, and chin-down, each stabilized with a corresponding thermoplastic mask. Seven isocenter positions were defined: one central position and six offset positions, each 5 cm away in a cardinal direction. Treatment plans incorporated multiple couch angles (0°, 30°, 45°, 60°, and 90°). The Catalyst⁺ HD system's accuracy was evaluated by comparing its detected displacements to predefined shifts applied using a HexaPOD evo RT system. Translational shifts of ±3 mm and rotational shifts of ±2° were introduced. Statistical analysis was conducted using the Wilcoxon signed-rank test.

Results: Under standard conditions (neutral posture, central isocenter, and 0° couch angle), the system demonstrated submillimeter accuracy (mean translational error: 0.08 mm; mean rotational error: 0.12°). Detection errors were significantly larger in the chin-up posture compared to the neutral posture (p=0.028). Similarly, a superior isocenter position resulted in considerably larger errors (p=0.026). A couch rotation of 30° led to a significant increase in error, whereas other couch angles maintained high precision.

Conclusion: The Catalyst⁺ HD system exhibits high accuracy for intracranial STI under most tested conditions. However, to optimize performance and accuracy, configurations involving a chin-up posture or a superior isocenter position should be avoided.