Effect of skin color on the setup of surface optical system in radiotherapy / 中华放射肿瘤学杂志

ABSTRACT

Objective:To investigate the sensitivity of the Catalyst HD in monitoring different skin colors, and assess the effect of skin color on the setup uncertainties using this system in radiotherapy.Methods:The standard cards guiding skin color and the cylinder model guiding quality control in radiotherapy were utilized to simulate the patients’ positioning. During the first monitoring, Catalyst HD was employed to acquire the image of the phantom as the reference image after conventional positioning (indoor laser+ phantom marking). When it was not the first monitoring, the couch was moved (-5 to 5 mm, step length of 2 mm) and Catalyst HD was adopted to obtain the surface image after conventional positioning. The bed deviation and corresponding setup errors monitored by Catalyst HD for different skin colors were recorded in the anterior-posterior (AP), superior-inferior (SI) and left-right (LR) direction, respectively.Results:During Catalyst HD monitoring, the integration time and gain were increased with the darker color. The logarithm of integration time and gain was significantly linearly negatively correlated with the same color ( R2>0.9). When the color difference with 1Y01SP was &Delta;E≤189, there was a significant correlation between the bed deviation and corresponding setup errors monitored by Catalyst HD in the SI and LR directions (R SI>0.5, R LR>0.5, R AP>0.9). The Catalyst HD monitoring was rapid and stable. When 218≤&Delta;E≤253, the correlation coefficients of them in the LR were R LR<0.3 and the Catalyst HD monitoring was stable. When 254≤&Delta;E≤285, the Catalyst HD failed to monitor stably. When &Delta;E>318, it failed to monitor this skin color. Conclusions:Gain, integration time and color have a certain correlation. The Catalyst HD can accurately monitor the setup errors within a specific range of skin color.