Parotid gland function after radiotherapy: the combined michigan and utrecht experience.
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.
Dijkema
Tim
T
Department of Radiotherapy, University Medical Center Utrecht, The Netherlands. T.Dijkema@umcutrecht.nl
Raaijmakers
Cornelis P J
CP
Ten Haken
Randall K
RK
Roesink
Judith M
JM
Braam
Pètra M
PM
Houweling
Anette C
AC
Moerland
Marinus A
MA
Eisbruch
Avraham
A
Terhaard
Chris H J
CH
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