Evaluation of the IDENTIFYTM Optical Surface Guidance System for Craniospinal Irradiation Patient Positioning
Abstract
Purpose
Craniospinal irradiation (CSI) can be delivered using a multi-isocentre technique. This requires a time-consuming alignment process using kV orthogonal imaging followed by cone-beam CT (CBCT) to ensure alignment accuracy across multiple anatomical regions. Surface guidance systems offer the potential to reduce imaging dose and setup time while maintaining alignment accuracy. This work investigates whether the IDENTIFY™ surface guidance system can provide alignment performance comparable to kV orthogonal and CBCT imaging for CSI patients.
Methods
An articulating anthropomorphic phantom fitted with a five-point mask was used as a surrogate CSI patient. The phantom was positioned on the treatment couch with intentional translational and angular offsets relative to its CT simulation reference position over 15 independent trials. For each setup, six-degree-of-freedom displacements of the head, abdomen, and pelvis were determined using kV orthogonal imaging, CBCT, and real-time output from IDENTIFY™. Differences between IDENTIFY™-reported displacements and those measured with kV orthogonal imaging and CBCT were used to assess alignment agreement across all anatomical regions and degrees of freedom.
Results
IDENTIFY™ demonstrated consistency with kV orthogonal and CBCT imaging. The maximum absolute mean differences between IDENTIFY™ and kV were 1.8 ± 0.7 mm translationally and 1.3 ± 0.4 degrees angularly across all anatomical regions and degrees of freedom. Likewise, the maximum absolute mean differences between IDENTIFY™ and CBCT were 1.6 ± 0.6 mm and 1.2 ± 0.5 degrees. All mean differences were within institutional alignment tolerances.
Conclusion
Surface-guided alignment using IDENTIFY™ showed consistency with established kV orthogonal and CBCT imaging methods in an anthropomorphic phantom. These results suggest that surface guidance may offer a viable alternative for CSI patient alignment, with the potential to reduce setup time and imaging dose. Ongoing work is evaluating workflow efficiency, time savings, and dose savings of IDENTIFY™ in CSI treatments, and trials on prospective patients are planned.