title: Tumor location, cirrhosis, and surgical history contribute to tumor movement in the liver, as measured during stereotactic irradiation using a real-time tumor-tracking radiotherapy system.
abstract: OBJECTIVE
  To investigate the three-dimensional (3D) intrafractional motion of liver tumors during real-time tumor-tracking radiotherapy (RTRT).
  
  
  METHODS
  The data of 20 patients with liver tumors were analyzed. Before treatment, a 2-mm gold marker was implanted near the tumor. The RTRT system used fluoroscopy image processor units to determine the 3D position of the implanted marker. A linear accelerator was triggered to irradiate the tumor only when the marker was located within a permitted region. The automatically recorded tumor-motion data were analyzed to determine the amplitude of the tumor motion, curve shape of the tumor motion, treatment efficiency, frequency of movement, and hysteresis. Each of the following clinical factors was evaluated to determine its contribution to the amplitude of movement: tumor position, existence of cirrhosis, surgical history, tumor volume, and distance between the isocenter and the marker.
  
  
  RESULTS
  The average amplitude of tumor motion in the 20 patients was 4 +/- 4 mm (range 1-12), 9 +/- 5 mm (range 2-19), and 5 +/- 3 mm (range 2-12) in the left-right, craniocaudal, and anterior-posterior (AP) direction, respectively. The tumor motion of the right lobe was significantly larger than that of the left lobe in the left-right and AP directions (p = 0.01). The tumor motion of the patients with liver cirrhosis was significantly larger than that of the patients without liver cirrhosis in the left-right and AP directions (p < 0.004). The tumor motion of the patients who had received partial hepatectomy was significantly smaller than that of the patients who had no history of any operation on the liver in the left-right and AP directions (p < 0.03). Thus, three of the five clinical factors examined (i.e., tumor position in the liver, cirrhosis, and history of surgery on the liver) significantly affected the tumor motion of the liver in the transaxial direction during stereotactic irradiation. Frequency analysis revealed that for 9 (45%) of the 20 tumors, the cardiac beat caused measurable motion. The 3D trajectory of the tumor showed hysteresis for 4 (20%) of the 20 tumors. The average treatment efficiency of RTRT was 40%.
  
  
  CONCLUSIONS
  Tumor location, cirrhosis, and history of surgery on the liver all had an impact on the intrafractional tumor motion of the liver in the transaxial direction. This finding should be helpful in determining the smallest possible margin in individual cases of radiotherapy for liver malignancy.
authors.affiliation: Department of Radiology, Hokkaido University School of Medicine, Sapporo, Japan. ktmr@radi.med.hokudai.ac.jp
authors.forename: Kei
authors.initials: K
authors.lastname: Kitamura
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
authors.forename: Yvette
authors.initials: Y
authors.lastname: Seppenwoolde
authors.forename: Tadashi
authors.initials: T
authors.lastname: Shimizu
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kodama
authors.forename: Hideho
authors.initials: H
authors.lastname: Endo
authors.forename: Rikiya
authors.initials: R
authors.lastname: Onimaru
authors.forename: Makoto
authors.initials: M
authors.lastname: Oda
authors.forename: Katsuhisa
authors.initials: K
authors.lastname: Fujita
authors.forename: Shinichi
authors.initials: S
authors.lastname: Shimizu
authors.forename: Kazuo
authors.initials: K
authors.lastname: Miyasaka
mesh_terms: D003199:Computer Systems; D005471:Fluoroscopy / Q000379:methods*; D006046:Gold; D006498:Hepatectomy; D006801:Humans; D021621:Imaging, Three-Dimensional; D008103:Liver Cirrhosis / Q000150:complications*; D008113:Liver Neoplasms / Q000150:complications / Q000000981:diagnostic imaging* / Q000601:surgery; D009038:Motion; D010315:Particle Accelerators; D019736:Prostheses and Implants; D016634:Radiosurgery; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000295:instrumentation / Q000379:methods*; D016896:Treatment Outcome
chemical_list: D006046:Gold