A comparison of dose-response models for the parotid gland in a large group of head-and-neck cancer patients.
OBJECTIVE
The dose-response relationship of the parotid gland has been described most frequently using the Lyman-Kutcher-Burman model. However, various other normal tissue complication probability (NTCP) models exist. We evaluated in a large group of patients the value of six NTCP models that describe the parotid gland dose response 1 year after radiotherapy.


METHODS
A total of 347 patients with head-and-neck tumors were included in this prospective parotid gland dose-response study. The patients were treated with either conventional radiotherapy or intensity-modulated radiotherapy. Dose-volume histograms for the parotid glands were derived from three-dimensional dose calculations using computed tomography scans. Stimulated salivary flow rates were measured before and 1 year after radiotherapy. A threshold of 25% of the pretreatment flow rate was used to define a complication. The evaluated models included the Lyman-Kutcher-Burman model, the mean dose model, the relative seriality model, the critical volume model, the parallel functional subunit model, and the dose-threshold model. The goodness of fit (GOF) was determined by the deviance and a Monte Carlo hypothesis test. Ranking of the models was based on Akaike's information criterion (AIC).


RESULTS
None of the models was rejected based on the evaluation of the GOF. The mean dose model was ranked as the best model based on the AIC. The TD(50) in these models was approximately 39 Gy.


CONCLUSIONS
The mean dose model was preferred for describing the dose-response relationship of the parotid gland.
Houweling
Antonetta C
AC
Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands. A.Houweling@umcutrecht.nl
Philippens
Marielle E P
ME
Dijkema
Tim
T
Roesink
Judith M
JM
Terhaard
Chris H J
CH
Schilstra
Cornelis
C
Ten Haken
Randall K
RK
Eisbruch
Avraham
A
Raaijmakers
Cornelis P J
CP
D004307:Dose-Response Relationship, Radiation; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D015233:Models, Statistical; D010306:Parotid Gland / Q000378:metabolism / Q000528:radiation effects*; D011446:Prospective Studies; D011832:Radiation Injuries / Q000150:complications*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods; D012062:Relative Biological Effectiveness; D012463:Saliva / Q000378:metabolism*; D013997:Time Factors; D014987:Xerostomia / Q000209:etiology