[A Study on LINAC Couch Position for Brain Stereotactic Radiotherapy Using High-definition Optical Surface Imaging System].

Purpose: The purpose of this study is to evaluate the detection accuracy of a high-definition optical surface imaging (OSI) system for non-coplanar radiotherapy (by rotating a phantom instead of a couch rotation).

Methods: The constancy, reproducibility, and accuracy of the positioning of the OSI system, Catalyst HD (CHD), for non-coplanar treatment were examined by rotating the head phantom around the isocenter. For all the tests, the phantom was rotated by ±30°, ±45°, ±60°, ±90° after correction of the phantom position within 0.0 mm±0.2 mm, and 0.0°±0.1° using Cone Beam CT (CBCT); the CBCT images were acquired again after rotation. We compared the phantom position derived from CHD, translational displacements of the isocenter (Dev.), and rotational displacements (Rot.) to the position derived from CBCT. The constancy of monitoring was evaluated by observing the variation in the isocenter position for 30 min. For evaluating reproducibility, the positions derived from CHD were compared with those from the planning data. The accuracy of positioning was evaluated by comparing CHD and CBCT findings after the couch rotation of ±0.5°.

Results: The constancy test revealed a maximum Rot. of 0.02±0.01° and Dev. of 0.20±0.08 mm, and the reproducibility test showed a maximum Rot. of 0.26±0.15° and Dev. of 0.93±0.26 mm. In the accuracy tests, when the phantom was further rotated by +0.5°, the maximum values were Rot. of 0.73±0.05° and Dev. of 0.35±0.15 mm; at -0.5°, the values were Rot. of -0.37±0.34° and Dev. of 0.43±0.24 mm.

Conclusion: A high-resolution OSI system is useful for position detection during treatment, even in non-coplanar irradiation.