title: Hybrid adaptive radiotherapy with on-line MRI in cervix cancer IMRT.
abstract: OBJECTIVE
  Substantial organ motion and tumor shrinkage occur during radiotherapy for cervix cancer. IMRT planning studies have shown that the quality of radiation delivery is influenced by these anatomical changes, therefore the adaptation of treatment plans may be warranted. Image guidance with off-line replanning, i.e. hybrid-adaptation, is recognized as one of the most practical adaptation strategies. In this study, we investigated the effects of soft tissue image guidance using on-line MR while varying the frequency of off-line replanning on the adaptation of cervix IMRT.
  
  
  METHODS
  33 cervical cancer patients underwent planning and weekly pelvic MRI scans during radiotherapy. 5 patients of 33 were identified in a previous retrospective adaptive planning study, in which the coverage of gross tumor volume/clinical target volume (GTV/CTV) was not acceptable given single off-line IMRT replan using a 3mm PTV margin with bone matching. These 5 patients and a randomly selected 10 patients from the remaining 28 patients, a total of 15 patients of 33, were considered in this study. Two matching methods for image guidance (bone to bone and soft tissue to dose matrix) and three frequencies of off-line replanning (none, single, and weekly) were simulated and compared with respect to target coverage (cervix, GTV, lower uterus, parametrium, upper vagina, tumor related CTV and elective lymph node CTV) and OAR sparing (bladder, bowel, rectum, and sigmoid). Cost (total process time) and benefit (target coverage) were analyzed for comparison.
  
  
  RESULTS
  Hybrid adaptation (image guidance with off-line replanning) significantly enhanced target coverage for both 5 difficult and 10 standard cases. Concerning image guidance, bone matching was short of delivering enough doses for 5 difficult cases even with a weekly off-line replan. Soft tissue image guidance proved successful for all cases except one when single or more frequent replans were utilized in the difficult cases. Cost and benefit analysis preferred (soft tissue) image guidance over (frequent) off-line replanning.
  
  
  CONCLUSIONS
  On-line MRI based image guidance (with combination of dose distribution) is a crucial element for a successful hybrid adaptive radiotherapy. Frequent off-line replanning adjuvantly enhances adaptation quality.
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada.
authors: Seungjong
authors: S
authors: Oh
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada.
authors: James
authors: J
authors: Stewart
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada.
authors: Joanne
authors: J
authors: Moseley
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada.
authors: Valerie
authors: V
authors: Kelly
authors: Department of Radiation Oncology, Liverpool Hospital, Sydney, Australia.
authors: Karen
authors: K
authors: Lim
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada.
authors: Jason
authors: J
authors: Xie
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada.
authors: Anthony
authors: A
authors: Fyles
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada; Department of Medical Biophysics, University of Toronto, Canada.
authors: Kristy K
authors: KK
authors: Brock
authors: RaySearch Laboratories AB, Stockholm, Sweden.
authors: Anna
authors: A
authors: Lundin
authors: RaySearch Laboratories AB, Stockholm, Sweden.
authors: Henrik
authors: H
authors: Rehbinder
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada.
authors: Michael
authors: M
authors: Milosevic
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada; Department of Medical Biophysics, University of Toronto, Canada.
authors: David
authors: D
authors: Jaffray
authors: Radiation Medicine Program, Princess Margaret Cancer Center, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Canada. Electronic address: young-bin.cho@rmp.uhn.on.ca.
authors: Young-Bin
authors: YB
authors: Cho
mesh_terms: D000328:Adult; D012809:Colon, Sigmoid / Q000033:anatomy & histology / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008875:Middle Aged; D009038:Motion; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012007:Rectum / Q000033:anatomy & histology / Q000528:radiation effects; D012189:Retrospective Studies; D001743:Urinary Bladder / Q000033:anatomy & histology / Q000528:radiation effects; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*
keywords: Adaptive radiotherapy; Cost and benefit; Dose accumulation; MR image guidance; Soft tissue matching