title: Clinical feasibility of using an EPID in CINE mode for image-guided verification of stereotactic body radiotherapy.
abstract: OBJECTIVE
  To introduce a novel method for monitoring tumor location during stereotactic body radiotherapy (SBRT) while the treatment beam is on by using a conventional electronic portal imaging device (EPID).
  
  
  METHODS
  In our clinic, selected patients were treated under a phase I institutional review board-approved SBRT protocol for limited hepatic metastases from solid tumors. Before treatment planning multiple gold fiducial markers were implanted on the periphery of the tumor. During treatment the EPID was used in cine mode to collect the exit radiation and produce a sequence of images for each field. An in-house program was developed for calculating the location of the fiducials and their relative distance to the planned locations.
  
  
  RESULTS
  Three case studies illustrate the utility of the technique. Patient A exhibited a systematic shift of 4 mm during one of the treatment beams. Patient B showed an inferior drift of the target of approximately 1 cm from the time of setup to the end of the fraction. Patient C had a poor setup on the first day of treatment that was quantified and accounted for on subsequent treatment days.
  
  
  CONCLUSIONS
  Target localization throughout each treatment beam can be quickly assessed with the presented technique. Treatment monitoring with an EPID in cine mode is shown to be a clinically feasible and useful tool.
authors: Department of Radiation Oncology, Dana-Farber/Brigham and Women's Cancer Center and Harvard Medical School, Boston, MA 02115, USA. rberbeco@lroc.harvard.edu
authors: Ross I
authors: RI
authors: Berbeco
authors: Fred
authors: F
authors: Hacker
authors: Dan
authors: D
authors: Ionascu
authors: Harvey J
authors: HJ
authors: Mamon
mesh_terms: D019583:Dose Fractionation, Radiation; D005240:Feasibility Studies; D006046:Gold; D006801:Humans; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000556:secondary; D009068:Movement; D010315:Particle Accelerators / Q000295:instrumentation*; D055585:Physical Phenomena; D010825:Physics; D019736:Prostheses and Implants; D011859:Radiography; D013238:Stereotaxic Techniques / Q000295:instrumentation* / Q000592:standards; D013679:Technology, Radiologic / Q000295:instrumentation / Q000379:methods
chemical_list: D006046:Gold