Differential processing of structured light projections for dynamic optical body surface sensing during radiation therapy

Complex radiotherapy techniques now rely on the positional integrity of the patient. Limited radiological image guidance for internal targeting is now being joined by optical surface sensing, which can measure the body surface throughout treatment. Fourier profilometry has dynamic surface reconstruction capability and provides a dense array of measured points without interpolation. In common with other surface sensing methods the effects of background illumination and skin texture need to be removed prior to surfaced reconstruction. Direct background measurement and subtraction is ideal for this, in a static environment. However, motion is challenging. This paper compares background subtraction and a new partial differential approach to processing structured light images for Fourier profilometry. Results are presented for an anthropomorphic test phantom and patient undergoing treatment. It is shown that in the static test case the differential approach produces surfaces comparable to the ideal case of background subtraction to better than 0.5mm with a reproducibility of 0.1mm under clinical conditions. Patient results show that the differential approach produces body reconstructions without motion artifacts in the presence of free breathing for data gathered at 25Hz, whereas background subtraction fails. Copyright © 2011 ACTA Press.