Unilateral versus bilateral irradiation in squamous cell head and neck cancer in relation to patient-rated xerostomia and sticky saliva

Background and purpose: To investigate the association between radiation technique with patient-rated moderate and severe xerostomia and sticky saliva. Materials and methods: One hundred and fifty patients treated with bilateral or unilateral irradiation for head and neck cancer were included. The salivary glands and the oral cavity were delineated on plannings-CT scans. Xerostomia and sticky saliva were assessed using the EORTC QLQ-H&N35 questionnaire at baseline and 6 and 12 months. Results: At 6 months a significant association between radiation technique and the mean parotid dose (MD_parb) and xerostomia was observed (Odds ratio (OR)-technique: 2.55; p = 0.04 and OR-MD_parb: 1.04; p = 0.009). Considering the individual salivary glands, only the mean dose in the contralateral parotid gland (MD_parcl) is associated with xerostomia (OR: 1.04; p < 0.0001). Moreover, the threshold dose for a 50% probability (P50) on xerostomia increased from 21 Gy with bilateral to 44 Gy for unilateral irradiation. Conclusions: Both technique and MD_parb influence the risk of xerostomia in irradiated patients. Of all individual salivary glands, only MD_parcl is of utmost importance for xerostomia. The shift in the P50 observed for xerostomia suggests that sparing of the contralateral parotid gland is compensated by hyperfunction of the contralateral parotid gland.