title: Implementation of adaptive radiation therapy for urinary bladder carcinoma: imaging, planning and image guidance.
abstract: BACKGROUND
  Adaptive radiation therapy (ART) for urinary bladder cancer has emerged as a promising alternative to conventional RT with potential to minimize radiation-induced toxicity to healthy tissues. In this work we have studied bladder volume variations and their effect on healthy bladder dose sparing and intrafractional margins, in order to refine our ART strategy.
  
  
  METHODS
  An online ART treatment strategy was followed for five patients with urinary bladder cancer with the tumors demarcated using Lipiodol(®). A library of 3-4 predefined treatment plans for each patient was created based on four successive computed tomography (CT) scans. Cone beam CT (CBCT) images were acquired before each treatment fraction and after the treatment at least weekly. In partial bladder treatment the sparing of the healthy part of the bladder was investigated. The bladder wall displacements due to bladder filling were determined in three orthogonal directions (CC, AP, DEX-SIN) using the treatment planning CT scans. An ellipsoidal model was applied in order to find the theoretical maximum values for the bladder wall displacements. Moreover, the actual bladder filling rate during treatment was evaluated using the CBCT images. Results. In partial bladder treatment the volume of the bladder receiving high absorbed doses was generally smaller with a full than empty bladder. The estimation of the bladder volume and the upper limit for the intrafractional movement of the bladder wall could be represented with an ellipsoidal model with a reasonable accuracy. Observed maximum growth of bladder dimensions was less than 10 mm in all three orthogonal directions during 15 minute interval.
  
  
  CONCLUSIONS
  The use of Lipiodol contrast agent enables partial bladder treatment with reduced irradiation of the healthy bladder volume. The ellipsoidal bladder model can be used for the estimation of the bladder volume changes and the upper limit of the bladder wall movement during the treatment fraction.
authors: Department of Oncology, Helsinki University Central Hospital , Helsinki , Finland.
authors: Laura
authors: L
authors: Tuomikoski
authors: Juha
authors: J
authors: Korhonen
authors: Juhani
authors: J
authors: Collan
authors: Jani
authors: J
authors: Keyriläinen
authors: Harri
authors: H
authors: Visapää
authors: Jukka
authors: J
authors: Sairanen
authors: Kauko
authors: K
authors: Saarilahti
authors: Mikko
authors: M
authors: Tenhunen
mesh_terms: D054893:Cone-Beam Computed Tomography; D019583:Dose Fractionation, Radiation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009367:Neoplasm Staging; D058958:Organs at Risk / Q000528:radiation effects; D011379:Prognosis; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided; D050397:Radiotherapy, Intensity-Modulated; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000473:pathology / Q000528:radiation effects*; D001749:Urinary Bladder Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*