title: Comparative analysis of an image-guided versus a non-image-guided setup approach in terms of delivered dose to the parotid glands in head-and-neck cancer IMRT.
abstract: OBJECTIVE
  To assess the impact of interfractional variations of shape and setup uncertainties on the dose to the parotid glands (PGs) in head-and-neck cancer intensity-modulated radiotherapy and image-guided radiotherapy (IGRT).
  
  
  METHODS
  Two scenarios were analyzed retrospectively for 10 head-and-neck cancer patients, treated with helical TomoTherapy (TomoTherapy Inc., Madison, WI): the IGRT scenario and the non-IGRT scenario. The initial dose-volume histograms derived from the planning computed tomography (PCT) scan and 120 recalculated dose-volume histograms of the PGs of each scenario and of corresponding fractions were compared. Setup errors, cumulative median doses (CMDs) for 6 fractions, overall volumes of the PGs, and volumes that received less than 1 Gy or more than 1.6 Gy per fraction were analyzed.
  
  
  RESULTS
  The mean decrease in the PG volume was 0.13 cm(3)/d. There was a significantly higher CMD than initially predicted (mean increase for 6 fractions, 1.13 Gy for IGRT and 0.96 Gy for non-IGRT). The volume that received less than 1 Gy per fraction decreased (mean difference to PCT, 1.36 cm(3) for IGRT [p = 0.003] and 1.35 cm(3) for non-IGRT [p = 0.003]) and the volume that received more than 1.6 Gy per fraction increased with increasing fraction number (mean difference to PCT, 1.14 cm(3) for IGRT [p = 0.01] and 1.16 cm(3) for non-IGRT [p = 0.006]). There was no statistically significant difference between the two scenarios (CMD, p = 0.095; volume that received <1 Gy per fraction, p = 0.896; and volume that received >1.6 Gy per fraction, p = 0.855).
  
  
  CONCLUSIONS
  In the analyzed group the actual delivered dose to the PGs does not differ significantly between an IGRT and a non-IGRT approach. However, IGRT in head-and-neck cancer intensity-modulated radiotherapy is strongly recommended to improve patient setup.
authors.affiliation: Department of Radiation Oncology, Klinikum rechts der Isar, Technische Universität München, München, Germany. Marciana.Duma@lrz.tu-muenchen.de
authors.forename: Marciana Nona
authors.initials: MN
authors.lastname: Duma
authors.forename: Severin
authors.initials: S
authors.lastname: Kampfer
authors.forename: Jan Jakob
authors.initials: JJ
authors.lastname: Wilkens
authors.forename: Tibor
authors.initials: T
authors.lastname: Schuster
authors.forename: Michael
authors.initials: M
authors.lastname: Molls
authors.forename: Hans
authors.initials: H
authors.lastname: Geinitz
mesh_terms: D000328:Adult; D000368:Aged; D019583:Dose Fractionation, Radiation; D005260:Female; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy; D010157:Palatal Neoplasms / Q000532:radiotherapy; D010306:Parotid Gland / Q000000981:diagnostic imaging / Q000528:radiation effects*; D011829:Radiation Dosage; D011859:Radiography; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012189:Retrospective Studies; D014067:Tonsillar Neoplasms / Q000532:radiotherapy