title: Use of implanted markers and interportal adjustment with real-time tracking radiotherapy system to reduce intrafraction prostate motion.
abstract: OBJECTIVE
  Interportal adjustment was applied to patients with prostate cancer using three fiducial markers and two sets of fluoroscopy in a real-time tumor-tracking radiotherapy (RTRT) system. The incidence of table position adjustment required to keep intrafractional uncertainty within 2.0 mm was investigated in this study.
  
  
  METHODS
  The coordinates of the center of gravity of the three fiducial markers were measured at the start of every portal irradiation in intensity-modulated radiotherapy (IMRT) with seven ports. The table position was adjusted to the planned position if the discrepancy was larger than 2.0 mm in the anterior-posterior (AP), cranial-caudal (CC), or left-right (LR) directions. In total, we analyzed 4,541 observations in 20 patients who received 70 Gy in 30 fractions (7.6 times a day on average).
  
  
  RESULTS
  The incidence of table position adjustment at 10 minutes from the initial setup of each treatment was 14.2%, 12.3%, and 5.0% of the observations in the AP, CC, and LR directions, respectively. The accumulated incidence of the table position adjustment was significantly higher at 10 minutes than at 2 minutes for AP (p = 0.0033) and CC (p = 0.0110) but not LR (p = 0.4296). An adjustment greater than 5 mm was required at least once in the treatment period in 11 (55%) patients.
  
  
  CONCLUSIONS
  Interportal adjustment of table position was required in more than 10% of portal irradiations during the 10-minute period after initial setup to maintain treatment accuracy within 2.0 mm.
authors.affiliation: Department of Radiation Medicine, Hokkaido University School of Medicine, Sapporo, Japan. sshimizu-rad@umin.ac.jp
authors.forename: Shinichi
authors.initials: S
authors.lastname: Shimizu
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Osaka
authors.forename: Nobuo
authors.initials: N
authors.lastname: Shinohara
authors.forename: Ataru
authors.initials: A
authors.lastname: Sazawa
authors.forename: Kentaro
authors.initials: K
authors.lastname: Nishioka
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Suzuki
authors.forename: Rikiya
authors.initials: R
authors.lastname: Onimaru
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shirato
mesh_terms: D058637:Examination Tables; D057918:Fiducial Markers; D006046:Gold; D006801:Humans; D008297:Male; D009068:Movement; D056888:Patient Positioning; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061106:Radiotherapy Setup Errors / Q000517:prevention & control; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods
chemical_list: D006046:Gold