SU‐GG‐T‐522: Investigation of Intracranial Localization for SRS and SRT Using MV‐CBCT

Abstract

Purpose: To investigate the accuracy and precision of Mega‐Voltage Cone Beam Computed Tomography (MV‐CBCT) localization for intracranial stereotactic treatment deliveries. Method and Materials: A Rando head phantom containing a metal ball bearing (BB) was mounted with a head frame. A treatment plan targeting the BB was generated and three localization methods were compared. The first, was the standard technique using laser micro‐alignment to the isocenter projected onto target positioning sheets. Second, a standard MV‐CBCT was acquired, using skull based registration with the treatment planning CT and millimeter precision correction using the motorized treatment couch. For the third, a micro‐adjustment of the head frame position using a Vernier scale was used to apply the MV‐CBCT correction with a 0.1 mm accuracy. After localization with each method was achieved, a series of 1.0 × 1.0 cm fields from gantry angles 0, 90, 180 and 270 degrees was used to asses target alignment by measuring the BB position relative to the beam central axis. Results: The standard localization technique resulted in an average displacement of the BB with respect to the beam central axis of 1.2 ± 0.1 mm. Skull‐based localization with MV‐CBCT using millimeter precision couch offsets resulted in a displacement of the BB with respect to the beam central axis of 2.3 mm. Localization with MV‐CBCT and micro‐adjustment resulted in a displacement of the BB with respect to the beam central axis of 1.2 ± 0.2 mm. Conclusion: After modifications were applied to the MV‐CBCT localization technique, accuracy was as good as the standard approach for head frame cases. When MV‐CBCT localization is applied to a frameless case, the anatomy‐based alignment eliminates the variability of interfraction patient positioning within the immobilizing mask.Conflict of Interest: Research partially funded by Siemens Medical Solutions.