Parotid gland-recovery after radiotherapy in the head and neck region - 36 months follow-up of a prospective clinical study

Abstract

The aim of the present study was to evaluate the recovery potential of the parotid glands after using either 3D-conformal-radiotherapy (3D-CRT) or intensity-modulated radiotherapy (IMRT) by sparing one single parotid gland. Between 06/2002 and 10/2008, 117 patients with head and neck cancer were included in this prospective, non-randomised clinical study. All patients were treated with curative intent. Salivary gland function was assessed by measuring stimulated salivary flow at the beginning, during and at the end of radiotherapy as well as 1, 6, 12, 24, and 36 months after treatment. Measurements were converted to flow rates and normalized relative to rates before treatment. Mean doses (D_mean) were calculated from dose-volume histograms based on computed tomographies of the parotid glands. Patients were grouped according to the D_mean of the spared parotid gland having the lowest radiation exposure: Group I - D_mean < 26 Gy (n = 36), group II - D_mean 26-40 Gy (n = 45), and group III - D_mean > 40 Gy (n = 36). 15/117 (13%) patients received IMRT. By using IMRT as compared to 3D-CRT the D_mean of the spared parotid gland could be significantly reduced (D_mean IMRT vs. 3D-CRT: 21.7 vs. 34.4 Gy, p < 0.001). The relative salivary flow rates (RFSR) as a function of the mean parotid dose after 24 and 36 months was in group I 66% and 74%, in group II 56% and 49%, and in group III 31% and 24%, respectively. Multiple linear regression analyses revealed that the parotid gland dose and the tumor site were the independent determinants 12 and 36 months after the end of RT. Patients of group I and II parotid gland function did recover at 12, 24, and 36 months after the end of RT. If a D_mean < 26 Gy for at least one parotid gland can be achieved then this is sufficient to reach complete recovery of pre-RT salivary flow rates. The radiation volume which depends on tumor site did significantly impact on the D_mean of the parotids, and thus on the saliva flow and recovery of parotid gland.