title: Motion and deformation of the target volumes during IMRT for cervical cancer: what margins do we need?
abstract: OBJECTIVE
  For cervical cancer patients the CTV consists of multiple structures, exhibiting complex inter-fraction changes. The purpose of this study is to use weekly MR imaging to derive PTV margins that accommodate these changes.
  
  
  METHODS
  Twenty patients with cervical cancer underwent a T2-weighted MRI exam before and weekly during IMRT. The CTV, GTV and surrounding organs were delineated. PTV margins were derived from the boundaries of the GTV and CTV in the six main directions and correlated with changes in the volumes of organs at risk.
  
  
  RESULTS
  Around the GTV a margin of 12, 14, 12, 11, 4 and 8mm to the anterior, posterior, right lateral, left lateral, superior and inferior directions was needed. The CTV required margins of 24, 17, 12, 16, 11 and 8 mm. The shift of the GTV and CTV in the AP directions correlated weakly with the change in rectal volume. For the bladder the correlations were even weaker.
  
  
  CONCLUSIONS
  We used weekly MRI scans to derive inhomogeneous PTV margins that accommodate changes in GTV and CTV. The weak correlations with rectum and bladder volume suggest that measures to control filling status of these organs may not be very effective.
authors.affiliation: Department of Radiation Oncology,University Medical Center Utrecht, The Netherlands. l.vandebunt@umcutrecht.nl
authors.forename: Linda
authors.initials: L
authors.lastname: van de Bunt
authors.forename: Ina M
authors.initials: IM
authors.lastname: Jürgenliemk-Schulz
authors.forename: Gérard A P
authors.initials: GA
authors.lastname: de Kort
authors.forename: Judith M
authors.initials: JM
authors.lastname: Roesink
authors.forename: Robbert J H A
authors.initials: RJ
authors.lastname: Tersteeg
authors.forename: Uulke A
authors.initials: UA
authors.lastname: van der Heide
mesh_terms: D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D016018:Least-Squares Analysis; D008279:Magnetic Resonance Imaging; D009038:Motion; D009367:Neoplasm Staging; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*