title: Impact of daily anatomical changes on EPID-based in vivo dosimetry of VMAT treatments of head-and-neck cancer.
abstract: OBJECTIVE
  Target dose verification for VMAT treatments of head-and-neck (H&N) cancer using 3D in vivo EPID dosimetry is expected to be affected by daily anatomical changes. By including these anatomical changes through cone-beam CT (CBCT) information, the magnitude of this effect is investigated.
  
  
  METHODS
  For 20 VMAT-treated H&N cancer patients, all plan-CTs (pCTs), 633 CBCTs and 1266 EPID movies were used to compare four dose distributions per fraction: treatment planning system (TPS) calculated dose and EPID reconstructed in vivo dose, both determined using the pCT and using the CBCT. D2, D50 and D98 of the planning target volume (PTV) were determined per dose distribution.
  
  
  RESULTS
  When including daily anatomical information, D2, D50 and D98 of the PTV change on average by 0.0±0.4% according to TPS calculations; the standard deviation of the difference between EPID and TPS target dose changes from 2.5% (pCT) to 2.1% (CBCT). Small time trends are seen for both TPS and EPID dose distributions when using the pCT, which disappear when including CBCT information.
  
  
  CONCLUSIONS
  Daily anatomical changes hardly influence the target dose distribution for H&N VMAT treatments according to TPS recalculations. Including CBCT information in EPID dose reconstructions slightly improves the agreement with TPS calculations.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands. Electronic address: r.rozendaal@nki.nl.
authors.forename: Roel A
authors.initials: RA
authors.lastname: Rozendaal
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Mijnheer
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Olga
authors.initials: O
authors.lastname: Hamming-Vrieze
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Anton
authors.initials: A
authors.lastname: Mans
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: Marcel
authors.initials: M
authors.lastname: van Herk
mesh_terms: D054893:Cone-Beam Computed Tomography; D006258:Head and Neck Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D006801:Humans; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted
keywords: Anatomical changes; EPID dosimetry; In vivo QA