title: Dosimetrically triggered adaptive intensity modulated radiation therapy for cervical cancer.
abstract: OBJECTIVE
  The widespread use of intensity modulated radiation therapy (IMRT) for cervical cancer has been limited by internal target and normal tissue motion. Such motion increases the risk of underdosing the target, especially as planning margins are reduced in an effort to reduce toxicity. This study explored 2 adaptive strategies to mitigate this risk and proposes a new, automated method that minimizes replanning workload.
  
  
  METHODS
  Thirty patients with cervical cancer participated in a prospective clinical study and underwent pretreatment and weekly magnetic resonance (MR) scans over a 5-week course of daily external beam radiation therapy. Target volumes and organs at risk (OARs) were contoured on each of the scans. Deformable image registration was used to model the accumulated dose (the real dose delivered to the target and OARs) for 2 adaptive replanning scenarios that assumed a very small PTV margin of only 3 mm to account for setup and internal interfractional motion: (1) a preprogrammed, anatomy-driven midtreatment replan (A-IMRT); and (2) a dosimetry-triggered replan driven by target dose accumulation over time (D-IMRT).
  
  
  RESULTS
  Across all 30 patients, clinically relevant target dose thresholds failed for 8 patients (27%) if 3-mm margins were used without replanning. A-IMRT failed in only 3 patients and also yielded an additional small reduction in OAR doses at the cost of 30 replans. D-IMRT assured adequate target coverage in all patients, with only 23 replans in 16 patients.
  
  
  CONCLUSIONS
  A novel, dosimetry-triggered adaptive IMRT strategy for patients with cervical cancer can minimize the risk of target underdosing in the setting of very small margins and substantial interfractional motion while minimizing programmatic workload and cost.
authors.affiliation: Department of Radiation Oncology, Liverpool Hospital, Sydney, Australia.
authors.forename: Karen
authors.initials: K
authors.lastname: Lim
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada.
authors.forename: James
authors.initials: J
authors.lastname: Stewart
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada; Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Valerie
authors.initials: V
authors.lastname: Kelly
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada.
authors.forename: Jason
authors.initials: J
authors.lastname: Xie
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan.
authors.forename: Kristy K
authors.initials: KK
authors.lastname: Brock
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada.
authors.forename: Joanne
authors.initials: J
authors.lastname: Moseley
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada; Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Young-Bin
authors.initials: YB
authors.lastname: Cho
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada; Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Anthony
authors.initials: A
authors.lastname: Fyles
authors.affiliation: RaySearch Laboratories AB, Stockholm, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Lundin
authors.affiliation: RaySearch Laboratories AB, Stockholm, Sweden.
authors.forename: Henrik
authors.initials: H
authors.lastname: Rehbinder
authors.affiliation: RaySearch Laboratories AB, Stockholm, Sweden.
authors.forename: Johan
authors.initials: J
authors.lastname: Löf
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada; Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada; Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; Techna Institute for the Advancement of Technology for Health, Toronto, Ontario, Canada.
authors.forename: David A
authors.initials: DA
authors.lastname: Jaffray
authors.affiliation: Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Ontario, Canada; Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada. Electronic address: mike.milosevic@rmp.uhn.ca.
authors.forename: Michael
authors.initials: M
authors.lastname: Milosevic
mesh_terms: D012809:Colon, Sigmoid; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D007421:Intestine, Small; D008279:Magnetic Resonance Imaging; D009068:Movement; D058958:Organs at Risk / Q000033:anatomy & histology; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000033:anatomy & histology; D047368:Tumor Burden; D001743:Urinary Bladder / Q000033:anatomy & histology; D002583:Uterine Cervical Neoplasms / Q000175:diagnosis / Q000473:pathology / Q000532:radiotherapy*