title: The effect of induction chemotherapy on tumor volume and organ-at-risk doses in patients with locally advanced oropharyngeal cancer.
abstract: OBJECTIVE
  To retrospectively report changes in gross tumor volume (GTV) and organ-at-risk (OAR) doses after induction chemotherapy (IC) in oropharyngeal cancer using different contouring strategies.
  
  
  METHODS
  GTV and OARs were delineated on pre- and post-IC planning CT. Two post-IC GTV contours were made: (1) a 'consensus set' using published guidelines (GTVconsensus), and (2) 'visible set', delineating only visible post-IC GTV (GTVvisible). Pre-IC interactively optimized volumetric modulated arc therapy plans were generated. The pre-IC planning constraints served as the starting point for both post-IC plans. Results reflect pooled data from all 10 patients.
  
  
  RESULTS
  Mean reduction in volume post-IC was 24% and 47% for consensus and visible primary tumor and 57% and 60% for consensus and visible nodes. Compared to pre-IC plans, average mean OAR dose for post-IC GTVconsensus plans was significantly lower for CL parotid. For GTVvisible plans both parotids, upper/lower larynx, inferior pharyngeal constrictor and cricopharyngeal muscles were significantly lower. However reductions compared with post-IC GTVconsensus plans were modest (1.6/1.5/1.2/3.7/5.9/2.6Gy, respectively).
  
  
  CONCLUSIONS
  IC in patients with oropharyngeal carcinoma results in substantial reductions in GTVs. If post-IC GTVs are used, which is contrary to current consensus, statistically significant but relatively small OAR dose reductions are observed.
authors.affiliation: Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands. Electronic address: p.doornaert@vumc.nl.
authors.forename: Patricia
authors.initials: P
authors.lastname: Doornaert
authors.forename: Max
authors.initials: M
authors.lastname: Dahele
authors.forename: Wilko F A R
authors.initials: WF
authors.lastname: Verbakel
authors.forename: Omar
authors.initials: O
authors.lastname: Bohoudi
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Slotman
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Langendijk
mesh_terms: D006801:Humans; D060828:Induction Chemotherapy; D058958:Organs at Risk; D009959:Oropharyngeal Neoplasms / Q000188:drug therapy* / Q000473:pathology* / Q000532:radiotherapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012189:Retrospective Studies; D047368:Tumor Burden / Q000187:drug effects*; D014987:Xerostomia / Q000209:etiology
keywords: Induction chemotherapy; Organ-at-risk dose; Oropharynx cancer; Volumetric change