title: Opto-electronic sensing of body surface topology changes during radiotherapy for rectal cancer.
abstract: OBJECTIVE
  The CT body surface underpins millimeter scale dose computation in radical radiotherapy. A lack of technology has prevented measurement of surface topology changes during irradiation. Consequently, body changes are incorporated into plans statistically. We describe the technology for dynamic measurement of continuous surface topology at submillimeter resolution and suggest appropriately modified planning.
  
  
  METHODS
  An interferometer casts cosinusoidal fringes across the surface of a patient on a treatment couch. Motion-induced changes to the spatial phase of the fringes are used to generate dynamic sequences of body height maps. Volume-conserving CT warping, guided by height change, is used to illustrate potential planning perturbations.
  
  
  RESULTS
  We present the results for a prone patient with rectal carcinoma. At most of the simultaneously measured 440 x 440 points in each of the 898 body height maps in a dynamic sequence, the standard deviations were <1-2 mm, with occasional points of 6 mm. Surface motion predominantly occurred along the small of the back. This motion was periodic and could take the spine and bladder across the 95% isodose contour.
  
  
  CONCLUSIONS
  Surface changes are most likely to be within 3 mm during irradiation, despite the effects of breathing and the discomfort of lying prone. The dosimetric effects are acceptable.
authors.affiliation: North Western Medical Physics, Christie Hospital NHS Trust, Manchester, United Kingdom. chris.moore@physics.cr.man.ac.uk
authors.forename: Christopher
authors.initials: C
authors.lastname: Moore
authors.forename: Francis
authors.initials: F
authors.lastname: Lilley
authors.forename: Veronique
authors.initials: V
authors.lastname: Sauret
authors.forename: Michael
authors.initials: M
authors.lastname: Lalor
authors.forename: David
authors.initials: D
authors.lastname: Burton
mesh_terms: D000465:Algorithms; D000886:Anthropometry / Q000295:instrumentation / Q000379:methods*; D018780:Body Surface Potential Mapping / Q000295:instrumentation / Q000379:methods*; D002138:Calibration; D002277:Carcinoma / Q000473:pathology / Q000503:physiopathology / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007368:Interferometry / Q000295:instrumentation; D007834:Lasers; D009038:Motion; D009068:Movement; D016684:Prone Position; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000532:radiotherapy*; D015203:Reproducibility of Results; D012119:Respiration; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed