Room: Exhibit Hall | Forum 9
Purpose: To identify the optimal cone-beam CT (CBCT) parameters for single fraction intracranial stereotactic radiosurgery (SRS) procedures for improved image guidance.
Methods: The imaging system of Varian TrueBeam STx linac allows creation of custom CBCT acquisition protocols. Four custom protocols were created, based on standard Head protocol provided by Varian, with different slice thickness, X-ray tube current, gantry rotation trajectory and speed. CBCT image acquisition of Catphan 504 phantom was done and images analyzed using Standard Imaging PipsPro program. Imaging analysis included effective slice thickness, high contrast resolution, low contrast visibility, uniformity and noise. Based on the results of the phantom analysis, one of the custom protocols was selected as default for single fraction stereotactic radiosurgery procedures and used for image guidance of treatment for several SRS patients. The clinical CBCT images were then compared to standard Head protocol provided by Varian.
Results: The results of Catphan 504 analysis show an improvement in image quality with increased CBCT projections which depend on gantry rotation span and speed. Increased X-ray tube current also resulted in improved image quality. The four custom protocols were compared on the basis of effective slice thickness, low contrast visibility, noise, and imaging dose, with optimal protocol selected as default for single fraction SRS procedures. There was also analysis done between CBCT images acquired with this custom protocol and standard Varian Head protocol, for several clinical SRS patients.
Conclusion: This work indicates the potential for improved image guidance for treatment of SRS patients by using optimal CBCT acquisition parameters.