Purpose: Surface guided imaging relies on exposure to a patient’s surface and anatomical topographic information to accurately track patient positioning for setup and to manage motion during treatment. Camera sensitivity parameters permit adjustments according to different reflections on the skin surface. In this study we attempt to quantify Integration time (µs) and Signal Amplification, or Gain (%) values with the CRAD Catalyst HD for four different skin tones.
Methods: Four ceramic skulls (Fun Express) were painted using four different shades of a matte mousse makeup foundation (Rimmel). We chose the darkest and lightest shades and two shades in between to simulate a variety of skin tones. A head cushion was molded to provide reproducible setup and positioning. Phantom was setup with and without the head rest and automatic camera sensitivity parameters were evaluated at multiple gantry angles (180⁰, 225⁰, 135⁰, and 360⁰).
Results: The average integration time generated by the automatic settings for no headrest in order from Lightest to Darkest tones were 2685µs, 2700µs, 4008µs, and 6608µs and the addition of a headrest decreased these values to 2562µs, 2686µs, 2007µs and 2109µs. The average Gain generated by the auto settings for no headrest in order from Lightest to Darkest tones were 167%, 363%, 314%, 321% and the addition of a headrest changed these values to 178%, 326%, 89%, 50%.
Conclusion: It is important to quantify camera sensitivity parameters for a variety of skin tones so that clinicians can rely on surface imaging for accurate positioning of patients at treatment time. Use of makeup foundation is a novel method for evaluating maximum imaging signal for a variety of skin tones. We demonstrated that darker skin tones required much greater integration time values than lighter skin tones to maximize surface reflection.