Effect of dose to parotid ducts on Sticky Saliva and Xerostomia in radiotherapy of head and neck squamous cell carcinoma

Radiotherapy (RT) in head and neck squamous cell cancer (HNSCC) often leads to sticky saliva and xerostomia (SSX). Dose sparing of salivary glands (SG) reduces occurrence of SSX but few studies investigated the relationship between RT dose to SG substructures and SSX. We therefore investigated this hypothesis, focusing on the parotid duct (PD). Retrospective data was collected from 99 HNSCC patients treated at our center with (chemo-)radiotherapy (CRT). PD and other organs-at-risk (OAR) were (re-)contoured and DVHs were generated without re-planning. SSX was graded according to CTCAE v.4.03 and evaluated at acute, subacute, and two late timepoints. Most patients presented with loco-regionally advanced disease. In 47% of patients, up-front neck dissection preceded CRT. Weighted mean dose was 28.6 Gy for bilateral parotid glands (PG), and 32.0 Gy for PD. Acute SSX presented as grades 0 (35.3%), I (41.4%), II (21.2%) and III (2.0%). There was no association of OARs and SSX ≥ grade 2 in univariable logistic regression (LR). Multivariable LR showed statistically significant relationship of acute SSX with: PG weighted mean dose (OR 0.84, p = 0.004), contralateral PG mean dose (OR 1.14, p = 0.02) and contralateral PD planning OAR (PD PRV) mean dose (OR 1.84, p = 0.03). There was an association of acute SSX with dose exposure of PD PRV in multivariable regression, only. Due to statistical uncertainties and the retrospective nature of this analysis, further studies are required to confirm or reject the hypothesis. A common strategy to prevent sticky saliva and xerostomia (SSX) in patients undergoing radiotherapy of the head and neck area is dose sparing of salivary gland parenchyma during treatment planning. It is largely unknown whether dose exposure of other salivary gland structures such as salivary ducts might play a role in the development of SSX. We performed a retrospective analysis of head and neck squamous cell carcinoma patients that were treated with curative-intent (chemo-)radiotherapy and investigated the association of parotid duct dose exposure and occurrence of SSX. Some analyzed parameters suggest a connection between parotid duct dose exposure and SSX but further studies will be necessary to confirm or reject these results.