title: Characterization and management of interfractional anatomic changes for pancreatic cancer radiotherapy.
abstract: OBJECTIVE
  To quantitatively characterize interfractional anatomic variations in pancreatic cancer radiotherapy (RT) and to study dosimetric advantages for using an online adaptive replanning scheme to account for these variations.
  
  
  METHODS
  Targets and organs at risk (OAR) were delineated by autosegmentation based on daily computed tomography (CT) images acquired using a respiration-gated in-room CT during daily image-guided RT (IGRT) for 10 pancreatic cancer patients. Various parameters, including the maximum overlap ratio (MOR) between the volumes based on planning and daily CTs for a structure, while the overlapping volumes were maximized, were used to quantify the interfractional organ deformation with the intrafractional variations largely excluded. An online adaptive RT (ART) was applied to these daily CTs. To evaluate the dosimetric benefits of ART, the dose distributions from the online ART were compared to those from the repositioning in the current standard IGRT practice.
  
  
  RESULTS
  The interfractional anatomic variations, particularly the organ deformation, are significant during pancreas irradiation. For the patients studied, the average MORs of all daily CTs were 80.2%, 61.7%, and 72.2% for pancreatic head, duodenum, and stomach, respectively. The online ART leads to improved dosimetric plan with better target coverage and/or OAR sparing than IGRT repositioning. For the patients studied, the mean V(50.4 Gy) (volume covered by 50.4 Gy) for the duodenum was reduced from 43.4% for IGRT to 15.6% for the online ART scheme.
  
  
  CONCLUSIONS
  The online adaptive RT scheme can effectively account for the significant interfractional anatomic variations observed in pancreas irradiation. The dosimetric advantages with the online ART may enable safe dose escalation in radiation therapy for pancreatic cancer.
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI 53226, USA.
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.forename: Beth
authors.initials: B
authors.lastname: Erickson
authors.forename: Cheng
authors.initials: C
authors.lastname: Peng
authors.forename: X Allen
authors.initials: XA
authors.lastname: Li
mesh_terms: D000465:Algorithms; D019583:Dose Fractionation, Radiation; D004386:Duodenum / Q000000981:diagnostic imaging; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging; D008099:Liver / Q000000981:diagnostic imaging; D009068:Movement; D058958:Organs at Risk / Q000000981:diagnostic imaging*; D010179:Pancreas / Q000000981:diagnostic imaging*; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D013270:Stomach / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden