Interferometric measurement of patient surface topology changes during therapy irradiation
Hampered by the lack of technology, detailed patient surface topology changes during radiotherapy have not been determined. This paper describes a structured light solution to dynamic surface measurement with an interferometer producing a fringe pattern across a treatment couch. Body surface topology alters the relative spatial phase content in the pattern, which can be used to generate relative surface heights. Triangulation of one surface point allows conversion to an absolute scale with half-millimetre resolution. By capturing fringe images at 25Hz, dynamic sequences of 898, 440×440 point height maps have been computed. For an example patient being treated for rectal carcinoma, standard deviations of surface heights are predominantly below 1mm, with 1% up to 2mm and occasional points as high as 6mm. Statistical summaries show movement concentrated along the arch of the back and within 3mm of the mean surface. Despite the prone position of the patient, the distance of the treatment site from the diaphragm and the small scale of motion , periodic breathing is clearly revealed.
KeywordsRadiotherapy topology measurement
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