SU‐GG‐J‐06: Optical and X‐Ray Image Guided Stereotactic Body Irradiator Dedicated to Small Animals

Purpose: To develop a dual modality, optical and x‐ray, image guided stereotactic irradiator, and to improve tumor visualization and the accuracy of target localization in small animal irradiation. Method and Materials: A bioluminescence (BL) optical imaging system has been integrated into an existing x‐ray image‐guided stereotactic irradiator developed previously by our group. The new system provides precise target localization and accurate radiation delivery in three dimensions. All localization procedures are computer‐controlled. An air‐cooled CCD camera with sufficiently reduced dark current for better signal‐to‐noise ratio is employed for bioluminescence imaging. The CCD camera is positioned off‐axis, in the same transverse plane as the x‐ray radiation axis. To acquire BL images, the animal is rotated through a 30 degree angle towards the camera, and then back to the original (treatment) position for the x‐ray imaging. The BL images are registered to the x‐ray images for image guidance. Results: The dual modality image guided irradiator was evaluated using an orthotopic lung tumor in a rat. The anterior and lateral BL images clearly showed the tumor with high contrast, while the same tumor was visible only in the anterior view in the x‐ray images. This indicated that the x‐ray image guidance alone is not sufficient to provide the precise localization. On the other hand, the registered BL and x‐ray images overcome this limitation by combining information of tumor position in the BL image with the anatomy in the x‐ray image. Conclusion: The accuracy of tumor localization in small animal SBRT is dramatically improved by integrating optical imaging with x‐ray imaging. The developed system also enhances the sparing of dose limiting normal tissues and organs‐at‐risk (OARs) and has facilitated accurate assessment of experiments in small animal SBRT investigations.