Long-term parotid gland function after radiotherapy.
OBJECTIVE
Irradiation of the parotid glands causes salivary dysfunction, resulting in reduced salivary flow. Recovery can be seen with time; however, long-term prospective data are lacking. The objective of this study was to analyze the long-term parotid gland function after irradiation for head-and-neck cancer.


METHODS
A total of 52 patients with head-and-neck cancer and treated with radiotherapy (RT) were prospectively evaluated. Stimulated bilateral parotid salivary flow rates were measured before RT and 6 weeks, 6 months, 12 months, and at least 3.5 years after RT completion. A complication was defined as a stimulated parotid flow rate of <25% of the pre-RT flow rate. The normal tissue complication probability model proposed by Lyman was fit to the data. Multilevel techniques were used to model the patterns of flow rates with time.


RESULTS
The mean stimulated flow rate of the parotid glands before RT was 0.31 mL/min (standard deviation [SD], 0.21). This was reduced to 0.14 mL/min (SD, 0.15) at 6 weeks after RT and recovered to 0.20 mL/min (SD, 0.22) at 6 months and 0.19 mL/min (SD, 0.21) at 12 months after RT. The mean stimulated flow rate was 0.25 mL/min (SD, 0.28) 5 years after RT. The mean dose to the parotid gland resulting in a 50% complication probability increased from 34 Gy at 6 weeks to 40 Gy at 6 months, 42 Gy at 12 months, and 46 Gy at 5 years after RT. Multilevel modeling indicated that both dose and time were significantly associated with the flow ratio.


CONCLUSIONS
Salivary output can still recover many years after RT. At 5 years after RT, we found an increase in the salivary flow rate of approximately 32% compared with at 12 months after RT.
Braam
Pètra M
PM
Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands. P.M.Braam@azu.nl
Roesink
Judith M
JM
Moerland
Marinus A
MA
Raaijmakers
Cornelis P J
CP
Schipper
Maria
M
Terhaard
Chris H J
CH
D000328:Adult; D000368:Aged; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010306:Parotid Gland / Q000503:physiopathology / Q000528:radiation effects*; D011446:Prospective Studies; D011879:Radiotherapy Dosage; D020127:Recovery of Function; D012472:Salivation / Q000502:physiology / Q000528:radiation effects*; D014987:Xerostomia / Q000503:physiopathology