title: Parotid gland function after radiotherapy: the combined michigan and utrecht experience.
abstract: OBJECTIVE
  To analyze the combined and updated results from the University of Michigan and University Medical Center Utrecht on normal tissue complication probability (NTCP) of the parotid gland 1 year after radiotherapy (RT) for head-and-neck (HN) cancer.
  
  
  METHODS
  A total of 222 prospectively analyzed patients with various HN malignancies were treated with conventional and intensity-modulated RT. Stimulated individual parotid gland flow rates were measured before RT and 1 year after RT using Lashley cups at both centers. A flow ratio <25% of pretreatment was defined as a complication. The data were fitted to the Lyman-Kutcher-Burman model.
  
  
  RESULTS
  A total of 384 parotid glands (Michigan: 157; Utrecht: 227 glands) was available for analysis 1 year after RT. Combined NTCP analysis based on mean dose resulted in a TD(50) (uniform dose leading to 50% complication probability) of 39.9 Gy and m (steepness of the curve) of 0.40. The resulting NTCP curve had good qualitative agreement with the combined clinical data. Mean doses of 25-30 Gy were associated with 17-26% NTCP.
  
  
  CONCLUSIONS
  A definite NTCP curve for parotid gland function 1 year after RT is presented, based on mean dose. No threshold dose was observed, and TD(50) was equal to 40 Gy.
authors.affiliation: Department of Radiotherapy, University Medical Center Utrecht, The Netherlands. T.Dijkema@umcutrecht.nl
authors.forename: Tim
authors.initials: T
authors.lastname: Dijkema
authors.forename: Cornelis P J
authors.initials: CP
authors.lastname: Raaijmakers
authors.forename: Randall K
authors.initials: RK
authors.lastname: Ten Haken
authors.forename: Judith M
authors.initials: JM
authors.lastname: Roesink
authors.forename: Pètra M
authors.initials: PM
authors.lastname: Braam
authors.forename: Anette C
authors.initials: AC
authors.lastname: Houweling
authors.forename: Marinus A
authors.initials: MA
authors.lastname: Moerland
authors.forename: Avraham
authors.initials: A
authors.lastname: Eisbruch
authors.forename: Chris H J
authors.initials: CH
authors.lastname: Terhaard
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D007928:Lethal Dose 50; D016013:Likelihood Functions; D008297:Male; D008824:Michigan; D008875:Middle Aged; D008954:Models, Biological; D009426:Netherlands; D010306:Parotid Gland / Q000503:physiopathology / Q000528:radiation effects*; D011446:Prospective Studies; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects* / Q000379:methods; D012472:Salivation / Q000502:physiology / Q000528:radiation effects*; D013997:Time Factors; D014987:Xerostomia / Q000209:etiology; D055815:Young Adult