Assessing the rigidity of thermoplastic masks for head immobilization effectiveness in stereotactic radiosurgery

This study compared three Brainlab thermoplastic masks-Cranial 4pi basic, stereotactic (Close Mask V2), and open-face-to see how well they limited head movement during Stereotactic Radiosurgery (SRS). Using a head phantom, we tested rotational movements (pitch, yaw, and roll) and measured displacements with the ExacTrac system. The open-face mask had the smallest mean displacements (pitch: 0.14 ± 0.03°, yaw: 0.11 ± 0.02°, roll: 0.16 ± 0.03°) and performed slightly better than the stereotactic mask in pitch (0.20 ± 0.04°, p = 0.0173). The stereotactic mask performed similarly in yaw (0.09 ± 0.02°) and roll (0.16 ± 0.04°). The basic mask showed much more movement (pitch: 0.44 ± 0.13°, yaw: 0.28 ± 0.07°, roll: 0.26 ± 0.07°), making it less suitable for SRS. These results apply to the solid two-piece masks tested here and show that both the open-face and stereotactic masks provide reliable immobilization for accurate SRS treatments.