The impacts of colors on the catalyst HD system: Gains, integral times, and setups in radiotherapy

Purpose: To build an image-scanning protocol of Catalyst HD and to investigate the impacts of different colors on gains (Ga), integral times (Ti), and setups using this system. Methods: Thirty-eight cards with different skin tones were studied, and the color difference ΔE was calculated based on a reference color in the RGB (R: red, G: green, B: blue) space. Correlations were investigated among ΔE, Ga, and Ti. After routine setup verification, the card position changed from −5 mm to 5 mm with a step size of 2 mm, and they were measured by Catalyst HD simultaneously. The position differences were calculated to evaluate setup errors. Results: As Ga changed from 100% to 1000%, the natural logarithmic function of Ti (lnTi) linearly decreased with a constant slope of −0.002. If the reference color had an RGB value of (200, 172, 153), lnTi increased linearly with slopes of 0.006 and 0.007 for the main and side cameras respectively, as ΔE increased. Moreover, there were significant positive correlations between measured positions and true values. The correlation coefficient rpos changed as a sigmoid function of ΔE. There was a ΔE threshold of 254.0 for color detection. The detection was different for different colors. Additionally, rpos depended on the RGB values, curvature, edge and area of a region-of-interest. Conclusions: There are close correlations among ΔE, Ga, and Ti, and ΔE has an impact on setup accuracy using Catalyst HD.