A novel surface imaging system for patient positioning and surveillance during radiotherapy A phantom study and clinical evaluation

Background. The use of optical surface positioning to support or replace X-ray-based image-guided radiotherapy (IGRT) may reduce patient exposure to extra dose. In specifically designed phantom tests, we analyzed the potential of a new scanning device preclinically. The system's clinical performance was evaluated in comparison to cone-beam computed tomography (CBCT) in a prospective study. Materials and methods. We first evaluated the scanning performance in terms of accuracy and reproducibility using phantom tests. An institutional review board (IRB)-approved clinical evaluation encompassing 224 fractions in 13 patients treated in three different regions (head and neck, thorax, pelvis) was then performed. Patients were first positioned using CBCT and then scanned with the Catalyst(TM) (C-RAD, Uppsala, Sweden) optical system to define the resulting difference vector. Results. Individual system settings are necessary for different scanning conditions. Reproducibility tests with phantoms showed a mean difference of 0.25 +/- 0.21 cm. Accuracy tests showed a mean difference of less than 0.52 +/- 0.41 cm. Considering all patients, clinical data showed residual target position differences between Catalyst(TM) (surface-driven) and CBCT (target-driven) systems within 0.07 +/- 0.28 cm/-aEuro parts per thousand 0.13 +/- 0.40 cm/0.15 +/- 0.36 cm/0.11 +/- 1.57A degrees/-aEuro parts per thousand 0.43 A +/- 1.68/-aEuro parts per thousand 0.10 A +/- 1.67A degrees (lateral/longitudinal/vertical/rotation/roll/pitch). Conclusion. Scanning quality depends on the color and shape of the scanned surface. Upon prospective clinical evaluation, excellent agreement between target- and contour driven positioning was observed. Catalyst(TM) may reduce CBCT scan frequency in patients where tumor location is fixed relative to the surface.