Setup Variations and Tumor Margins Using the ExacTrac X-Ray 6D in Prostate Radiotherapy

摘要

The purposes of this study are to investigate setup variations for translational and rotational movements using the ExacTrac X-ray 6D image-guided system and to evaluate their impact on tumor margins in prostate radiotherapy. Five patients with prostate cancer who had been treated with ExacTrac X-ray 6D system were involved in this study. For each patient, after the images were obtained from X-ray devices and fused with digitally reconstructed images, setup variations for translational and rotational movements were investigated. From these variations, systematic and random errors were calculated and their impact on tumor margins was evaluated. Based on the bony landmarks, means and standard deviations of translational variations in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) directions were -0.8±1.8, 0.6±2.0, and -0.2±0.3 mm, respectively. Rotational variations were 0.24±0.19, 0.05±0.30, 0.63±0.61 degrees along the yaw, roll, and pitch directions, respectively. Tumor margins due to setup variations were calculated as S.S, 6.0, and 1.5 mm in the AP, SI and LR directions, respectively. Image-guided function with ExacTrac X-ray 6D system was useful for the investigation of setup variations. Their influence on tumor margins was also evaluated for prostate radiotherapy. To apply tumor margin clinically, other errors such as interfractional one should be further considered.