Development of dedicated phantom for end-to-end testing of multiple image-guidance configurations incorporating light-section-based surface guidance system

PURPOSE

Radiotherapy devices with multiple image-guidance systems, such as surface-guided radiation therapy (SGRT), have been widely used in recent years. However, in the case of SGRT devices using the light-section method, coordinate coincidence evaluation using a phantom for SGRT devices with patterned light projection is not appropriate. Hence, this study aims to develop a dedicated phantom able to evaluate both the detection accuracy and coordinate coincidence of multiple IGRT configurations, including light-section-based SGRT devices.

MATERIALS AND METHOD

First, we developed an end-to-end (E2E) phantom that can be scanned by CT and detected by a light-section-method-based SGRT device. Second, the detection accuracy of the phantom under three reference data acquisition conditions was evaluated using the E2E phantom. The three conditions were a body surface image detected by VOXELAN in the simulation CT room, a body surface image reconstructed from the volume data of the simulation CT room, and a body surface image acquired by VOXELAN in the radiotherapy room. Finally, the coordinate coincidence of the image-guidance system was evaluated using the E2E phantom.

RESULT

Upon comparing detection accuracy among the three reference data acquisition methods, we found that the reference data generated in the CT room had the largest error (0.58 mm at maximum). The coordinate coincidences of the multiple image-guidance systems were within 1 mm for all components after the maintenance of VOXELAN using E2E phantom. Furthermore, the long-term direction stability was worse in the longitudinal direction.

CONCLUSION

The new E2E phantom can be used to evaluate the detection accuracy of a light-section-based SGRT system and the coordinate coincidence using a Winston-Lutz-based method in multiple image-guided configurations. The detection accuracy in the three different reference images of VOXELAN using this phantom improved to within 1 mm in all directions.

Improvement of patient localization repeatability using a light-section based optical surface guidance system in a pre-positioning procedure

PURPOSE

Surface-guided radiotherapy is useful for the pre-positioning and monitoring of radiotherapy. The purpose of this study was to investigate the impact of surface guidance on the repeatability of patient localization and to estimate the specific point at which high positional errors occur.

MATERIALS AND METHODS

Ten patients without the VOXELAN system (non-VXLN group) and 10 patients with the VOXELAN as the pre-positioning procedure (VXLN group) were included in this analysis. Twelve regions of interest (ROI) were defined in all the patients to verify any misalignment during radiotherapy. Thirteen ROIs were defined on the isocenter.

RESULTS

Compared with the non-VXLN group, the translational positional errors of the VXLN group were the same for all the ROIs. The mean translational positional errors of the VXLN group in the longitudinal direction were approximately 0.1mm, and the standard deviation was the largest among the three directions in all the ROIs. The magnitude of the standard deviation in the non-VXLN group varied independently of the ROI and direction. The standard deviations of the VXLN group in the longitudinal direction were large in all the ROIs, while the standard deviations in the vertical and lateral directions were small.

CONCLUSION

Pre-positioning with a surface guidance system reduced the body twist and rotation, which could not be corrected by image-guided radiotherapy alone. Since the VOXELAN can detect positioning errors quickly and without additional radiation exposure to the patient, it can be used as a tool for pre-positioning in radiotherapy.