title: Development of a phantom to evaluate the positioning accuracy of patient immobilization systems using thermoplastic mask and polyurethane cradle.
abstract: OBJECTIVE
  The purpose of this study was to develop a new phantom to evaluate the positioning accuracy of patient immobilization systems.
  
  
  METHODS
  The phantom was made of papers formed into a human shape, paper clay, and filling rigid polyester. Acrylonitrile butadiene styrene (ABS) pipes were inserted at anterior-posterior (A-P) and right-left (R-L) directions in the phantom to give static load by pulling ropes through the pipes. First, the positioning precision of the phantom utilizing a target locating system (TLS) was evaluated by moving the phantom on a couch along inferior-superior (I-S), A-P, and R-L directions in a range from -5 mm to +5 mm. The phantom's positions detected with the TLS were compared with values measured by a vernier caliper. Second, the phantom movements in a tensile test were chosen from patient movements determined from 15 patients treated for intracranial lesions and immobilized with a thermoplastic mask and polyurethane cradle. The phantom movement was given by minimum or maximum values of patient movements in each direction. Finally, the relationship between phantom movements and the static load in the tensile test was characterized from measurements using the new phantom and the TLS.
  
  
  RESULTS
  The differences in all positions between the vernier caliper measurement and the TLS detected values were within 0.2 mm with frequencies of 100%, 95%, and 90% in I-S, A-P, and R-L directions, respectively. The phantom movements according to patient movements in clinical application in I-S, A-P, and R-L directions were within 0.58 mm, 0.94 mm, and 0.93 mm from the mean value plus standard deviation, respectively. The regression lines between the phantom movements and static load were given by y = 0.359x, y = 0.241x, and y = 0.451x in I-S, A-P, and R-L directions, respectively, where x is the phantom movement (mm) and y is the static load (kgf). The relationship between the phantom movements and static load may represent the performance of inhibiting patient movements, so the accuracy of the immobilization system in the intracranial lesion will be estimated in advance by basic tensile test on the new phantom.
  
  
  CONCLUSIONS
  The newly developed phantom was useful to evaluate the accuracy of immobilization systems for a Cyberknife system for intracranial lesions.
authors: Department of Radiology, Saiseikai Imabari Hospital, Imabari, Ehime, Japan.
authors: Hiroki
authors: H
authors: Inata
authors: Takatoshi
authors: T
authors: Semba
authors: Yoshihiro
authors: Y
authors: Itoh
authors: Yuta
authors: Y
authors: Kuribayashi
authors: Suetoshi
authors: S
authors: Murayama
authors: Osamu
authors: O
authors: Nishizaki
authors: Fujio
authors: F
authors: Araki
mesh_terms: D001513:Beds; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D007103:Immobilization / Q000295:instrumentation*; D056888:Patient Positioning / Q000295:instrumentation*; D019047:Phantoms, Imaging; D010969:Plastics; D011140:Polyurethanes; D016634:Radiosurgery / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*
chemical_list: D010969:Plastics; D011140:Polyurethanes