3D dynamic body surface sensing and CT-body matching: a tool for patient set-up and monitoring in radiotherapy.

Recent advances in radical broad-beam conformal radiotherapy for disease at non-rigid sites suggest that the treatment room set-up of patients should be performed using the CT-plan digital body surface as a reference standard. In effect, the CT-plan surface is a "virtual shell" and should be used as such. To do this requires 3D body surface information to be captured live in the treatment room and then manipulated for comparison with the CT virtual shell. To address this situation, a near real-time prototype opto-electronic dynamic 3D surface sensor has been developed and equipped with a novel software utility for visualizing and matching the disparate surfaces arising from planning and treatment environments. Using the CT virtual shell and height-maps produced by the sensor, a two-phase 3D positioning strategy for patient set-up and monitoring is described. Phase one is an image-guided manual "approach". Phase two is automated "docking" using simulated annealing to determine optimum set-up corrections. The concepts and implementation are illustrated using archival patient data and an anthropomorphic phantom "patient" in a treatment room environment.