Assessment of Image Guidance Using kV Orthogonal Images and Cone Beam CT for Liver Stereotactic Radiosurgery

Abstract

To assess the accuracy of image guidance using 2D kilovoltage (kV) imaging and 3D cone-beam CT (CBCT), we quantified and evaluated the inter-fractional changes in setup position of forty five patients treated with stereotactic radiosurgery (SRS) for liver cancer. All patients in this study had three gold seed implanted near the tumor and received 4DCT scan to quantify respiratory motion. Images corresponding to the end exhale phase were used as primary reference images for tumor delineation, treatment plan and patient setup. After patient setup using conventional skin marker and lasers, kV orthogonal images were acquired at end-exhale, and then CBCT procedure was performed. The acquired images from a total of 135 sessions were aligned to primary reference images and the results of displacement were compared and analyzed. The average displacement with conventional setup was Vrt = 0.0 ± 3.7, Lat = 0.4 ± 2.6, and Lng = -3.0 ± 6.0 mm and Vrt = -0.5 ± 4.0, Lat = 0.4 ± 4.0, and Lng = -3.8 ± 6.0 mm for 2D and 3D alignment, respectively. The average magnitude of displacement vector was 7.0 ± 3.8 and 8.0 ± 4.3 mm, respectively. Their linear correlation between 2D and 3D alignment was strong; R2 was 0.737, 0.745, and 0.746 at vertical, lateral, and longitudinal direction, respectively. However the slope of the estimated regression line was less than 1. Compared with patient setup using CBCT, the residual displacements in liver position on kV orthogonal images were Vrt = -0.2 ± 2.4, Lat = -0.01 ± 2.2, and Lng = -0.5 ± 3.4 mm on the average, respectively.