title: Combined online and offline adaptive radiation therapy: a dosimetric feasibility study.
abstract: OBJECTIVE
  The purpose of this work is to explore a new adaptive radiation therapy (ART) strategy, combined "online and offline" ART, that can fully account for interfraction variations similar to the existing online ART but with substantially reduced online effort.
  
  
  METHODS
  The concept for the combined ART is to perform online ART only for the fractions with obvious interfraction variations and to deliver the ART plan for that online fraction as well as the subsequent fractions until the next online fraction needs to be adapted. To demonstrate the idea, the daily computed tomographic (CT) data acquired during image guided radiation therapy (IGRT) with an in-room CT (CTVision, Siemens Healthcare, Amarillo, TX) for 6 representative patients (including 2 prostate, 1 head-and-neck, and 1 pancreatic cancer, 1 adrenal carcinoma, and 1 craniopharyngioma patients) were analyzed. Three types of plans were generated based on the following selected daily CTs: (1) IGRT repositioning plan, generated by applying the repositioning shifts to the original plan (representing the current IGRT practice); (2) Re-Opt plan, generated with full-scope optimization; and (3) ART plan, either online ART plan generated with an online ART tool (RealArt, Prowess Inc, Concord, CA) or offline ART plan generated with shifts from the online ART plan. Various dose-volume parameters were compared with measure dosimetric benefits of the ART plans based on daily dose distributions and the cumulative dose maps obtained with deformable image registration.
  
  
  RESULTS
  In general, for all the cases studied, the ART (with 3-5 online ART) and Re-Opt plans provide comparable plan quality and offer significantly better target coverage and normal tissue sparing when compared with the repositioning plans. This improvement is statistically significant.
  
  
  CONCLUSIONS
  The combined online and offline ART is dosimetrically equivalent to the online ART but with substantially reduced online effort, and enables immediate delivery of the adaptive plan when an obvious anatomic change is observed.
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin; Henan Cancer Hospital, Zhengzhou University, Zhengzhou, China.
authors.forename: Chengliang
authors.initials: C
authors.lastname: Yang
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Feng
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Ergun
authors.initials: E
authors.lastname: Ahunbay
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Yu-Wen
authors.initials: YW
authors.lastname: Chang
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Colleen
authors.initials: C
authors.lastname: Lawton
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Christopher
authors.initials: C
authors.lastname: Schultz
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Dian
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Selim
authors.initials: S
authors.lastname: Firat
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin.
authors.forename: Beth
authors.initials: B
authors.lastname: Erickson
authors.affiliation: Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin. Electronic address: ali@mcw.edu.
authors.forename: X Allen
authors.initials: XA
authors.lastname: Li
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D009369:Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*