Head-to-head: Anthropomorphic phantoms for evaluating the effect of skin tone on the accuracy of surface imaging systems

To study the localization accuracy of two commercial surface imaging (SI) systems used for intrafraction motion monitoring during stereotactic radiosurgery (SRS) and quantify the difference in accuracy due to skin tone.

Using a publicly available CT dataset, anthropomorphic phantoms were 3D printed using filament in four skin tones: rose tan, light brown, medium brown, and dark brown (3DUniverse, Chicago, IL, USA). Three SI systems from two vendors were utilized to measure the SI-reported offsets of the stationary phantoms in various gantry and couch configurations to create SRS-like conditions, including when the gantry obscured one camera pod. At each position, approximately 5 s of offsets were averaged to obtain the SI-reported offset.

All SI systems reported larger offsets for all phantoms at non-zero couch angles. The medium brown and dark brown phantoms showed the largest magnitudes at non-zero couch angles, increasing further when a camera pod was obstructed. For two SI systems, the position of the phantom for medium and dark brown phantoms could not be resolved at certain gantry/couch positions, and offsets up to 5 mm were reported.

Characterization of SI systems using 3D-printed phantoms in a spectrum of skin tones can be used to determine the accuracy of SI tracking under treatment-like conditions. All SI systems showed decreased accuracy with darker skin-toned phantoms, which increased with an obstructed camera view.