title: Stereotactic body radiation therapy for liver tumors: impact of daily setup corrections and day-to-day anatomic variations on dose in target and organs at risk.
abstract: OBJECTIVE
  To assess day-to-day differences between planned and delivered target volume (TV) and organ-at-risk (OAR) dose distributions in liver stereotactic body radiation therapy (SBRT), and to investigate the dosimetric impact of setup corrections.
  
  
  METHODS
  For 14 patients previously treated with SBRT, the planning CT scan and three treatment scans (one for each fraction) were included in this study. For each treatment scan, two dose distributions were calculated: one using the planned setup for the body frame (no correction), and one using the clinically applied (corrected) setup derived from measured tumor displacements. Per scan, the two dose distributions were mutually compared, and the clinically delivered distribution was compared with planning. Doses were recalculated in equivalent 2-Gy fraction doses. Statistical analysis was performed with the linear mixed model.
  
  
  RESULTS
  With setup corrections, the mean loss in TV coverage relative to planning was 1.7%, compared with 6.8% without corrections. For calculated equivalent uniform doses, these figures were 2.3% and 15.5%, respectively. As for the TV, mean deviations of delivered OAR doses from planning were small (between -0.4 and +0.3 Gy), but the spread was much larger for the OARs. In contrast to the TV, the mean impact of setup corrections on realized OAR doses was close to zero, with large positive and negative exceptions.
  
  
  CONCLUSIONS
  Daily correction of the treatment setup is required to obtain adequate TV coverage. Because of day-to-day patient anatomy changes, large deviations in OAR doses from planning did occur. On average, setup corrections had no impact on these doses. Development of new procedures for image guidance and adaptive protocols is warranted.
authors.affiliation: Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands. a.mendezromero@erasmusmc.nl
authors.forename: Alejandra
authors.initials: A
authors.lastname: Méndez Romero
authors.forename: Roel Th
authors.initials: RT
authors.lastname: Zinkstok
authors.forename: Wouter
authors.initials: W
authors.lastname: Wunderink
authors.forename: Rob M
authors.initials: RM
authors.lastname: van Os
authors.forename: Hans
authors.initials: H
authors.lastname: Joosten
authors.forename: Yvette
authors.initials: Y
authors.lastname: Seppenwoolde
authors.forename: Peter J C M
authors.initials: PJ
authors.lastname: Nowak
authors.forename: Rene P
authors.initials: RP
authors.lastname: Brandwijk
authors.forename: Cornelis
authors.initials: C
authors.lastname: Verhoef
authors.forename: Jan N M
authors.initials: JN
authors.lastname: IJzermans
authors.forename: Peter C
authors.initials: PC
authors.lastname: Levendag
authors.forename: Ben J M
authors.initials: BJ
authors.lastname: Heijmen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004386:Duodenum / Q000528:radiation effects; D005260:Female; D006801:Humans; D016014:Linear Models; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000556:secondary / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011832:Radiation Injuries / Q000517:prevention & control; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D013270:Stomach / Q000528:radiation effects; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden