title: Four-dimensional treatment planning and fluoroscopic real-time tumor tracking radiotherapy for moving tumor.
abstract: OBJECTIVE
  To achieve precise three-dimensional (3D) conformal radiotherapy for mobile tumors, a new radiotherapy system and its treatment planning system were developed and used for clinical practice.
  
  
  METHODS
  We developed a linear accelerator synchronized with a fluoroscopic real-time tumor tracking system by which 3D coordinates of a 2.0-mm gold marker in the tumor can be determined every 0.03 second. The 3D relationships between the marker and the tumor at different respiratory phases are evaluated using CT image at each respiratory phase, whereby the optimum phase can be selected to synchronize with irradiation (4D treatment planning). The linac is triggered to irradiate the tumor only when the marker is located within the region of the planned coordinates relative to the isocenter.
  
  
  RESULTS
  The coordinates of the marker were detected with an accuracy of +/- 1 mm during radiotherapy in the phantom experiment. The time delay between recognition of the marker position and the start or stop of megavoltage X-ray irradiation was 0.03 second. Fourteen patients with various tumors were treated by conformal radiotherapy with a "tight" planning target volume (PTV) margin. They were surviving without relapse or complications with a median follow-up of 6 months.
  
  
  CONCLUSIONS
  Fluoroscopic real-time tumor tracking radiotherapy following 4D treatment planning was developed and shown to be feasible to improve the accuracy of the radiotherapy for mobile tumors.
authors.affiliation: Department of Radiology, Hokkaido University School of Medicine, Sapporo, Japan. hshirato@radi.med.hokudai.ac.jp
authors.forename: H
authors.initials: H
authors.lastname: Shirato
authors.forename: S
authors.initials: S
authors.lastname: Shimizu
authors.forename: K
authors.initials: K
authors.lastname: Kitamura
authors.forename: T
authors.initials: T
authors.lastname: Nishioka
authors.forename: K
authors.initials: K
authors.lastname: Kagei
authors.forename: S
authors.initials: S
authors.lastname: Hashimoto
authors.forename: H
authors.initials: H
authors.lastname: Aoyama
authors.forename: T
authors.initials: T
authors.lastname: Kunieda
authors.forename: N
authors.initials: N
authors.lastname: Shinohara
authors.forename: H
authors.initials: H
authors.lastname: Dosaka-Akita
authors.forename: K
authors.initials: K
authors.lastname: Miyasaka
mesh_terms: D003199:Computer Systems; D005240:Feasibility Studies; D005471:Fluoroscopy / Q000379:methods*; D006046:Gold; D006801:Humans; D009068:Movement; D009369:Neoplasms / Q000532:radiotherapy*; D010315:Particle Accelerators; D019736:Prostheses and Implants; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*
chemical_list: D006046:Gold