A novel method of determining a body surface for collision detection using CT localization radiograph

In previous studies, identifying a position at high collision risk outside a range of CT imaging requires a cost, such as an infrared camera. In this study, we propose a simple method to identify the patient's body surface using localization radiographs in a planning CT that are available at any facility. Five metallic markers were attached to the mannequin's right elbow with the arm up. Twelve localization radiographs were acquired at 30° intervals from 0° to 330° of the tube angle. The images acquired at 60°, 90°, 120°, 150°, 180°, 270°, 300°, and 330° of the tube angle were used to estimate the metallic markers' position. The three-dimensional (3D) estimated coordinate (EC) of the metallic markers (X, Y, Z) was calculated from the two selected localization radiographs and compared to the reference coordinate (RC). The average of the difference between the EC and the RC was [Formula: see text] -  1.4 ± 3.5 mm, [Formula: see text] = - 3.1 ± 6.2 mm and [Formula: see text] = 0.8 ± 0.5 mm. When the set of combined tube angles (α, β) was (60°,270°), (120°,300°), and (180°,330°), the average distance between RC and EC exceeded 10.0 mm. The maximum distance between RC and EC was 46.7 mm. The distance between the mannequin's elbow and the gantry surface estimated by the TPS differed by 0.2 cm compared with the direct measurement in the treatment room. This study proposed a novel method for estimating patient body surface coordinates using localization radiographs, with sufficient accuracy to prevent collisions between the patient's body surface and the gantry.