Three-dimensional surface scanning of patients to extend computed tomography field of view and scan length for dose calculation and collision avoidance in radiotherapy treatment planning.

BACKGROUND: Radiotherapy treatment planning requires knowledge of a patient's anatomical surface for use in dose calculations, collision checks, or surface-guided radiation therapy (SGRT). This information is usually obtained from a computed tomography (CT) scan which may encounter field-of-view (FOV) limitations or require additional radiation dose beyond the treatment area to capture the full patient habitus. PURPOSE: This study demonstrates an affordable alternative solution to obtain a patient's surface information without CT or room mounted surface-guidance imaging cameras for the purpose of detecting patient collisions and providing additional skin surface information needed for appropriate depth calculations of clipped FOV scans. METHODS: Three-dimensional (3D) surface models of five patients were acquired immediately prior to CT simulation using an iPad Air 2 equipped with a Structure Sensor Pro and Monocle SS application. The 3D surfaces were manually registered to the CT images and nearest distances between CT surface and 3D surface were calculated. Nearest distance calculations were also performed with a 2 mm CT rind structure that excluded select regions not relevant to surface detection. To demonstrate the advantage of having additional scan length for clearance checks, a collision simulated plan was evaluated with a shortened CT scan length versus with additional 3D surface information. RESULTS: CT rind to 3D scan surface mean distances for each patient were 1.65 mm, 0.99 mm, -0.93 mm, -0.79 mm, and -1.53 mm with standard deviations of 6.51 mm, 6.71 mm, 3.38 mm, 2.84 mm, and 2.69 mm. CONCLUSION: This study demonstrates the feasibility of an accessible low-cost 3D surface scanning solution to supplement clipped field-of-view CT scans and reduce CT scan lengths by obtaining important patient surface data for improved calculation accuracy, treatment clearance checks, and SGRT.