ESTRO 2021 Abstract Book

S374

ESTRO 2021

Denmark; 2 University of Copenhagen, Department of Odontology, Section of Oral Biology and Immunopathology, Copenhagen, Denmark; 3 Herlev Hospital, Department of Oncology, Herlev, Denmark; 4 Zealand University Hospital, Naestved Sygehus, Naestved, Denmark; 5 Odense University Hospital, Department of Oncology, Odense, Denmark; 6 University of Southern Denmark, Department of Clinical Research, Odense, Denmark Purpose or Objective Xerostomia is a common complaint in patients treated with radiotherapy (RT) for head and neck cancer (HNC), often having a negative impact on quality of life. It is suggested that mean doses above 39 Gy to the parotid glands lead to irreversible damage of the glands, resulting in a permanent reduction of saliva flow rates and xerostomia . The aim of this study is to investigate associations between mean dose to the parotid glands, change in salivary flow and severity of xerostomia one year after RT. Materials and Methods 19 patients (aged 62±9 years) treated with RT for HNC were assessed. The patients were examined before the first RT fraction (Time 1), immediately after completion of the RT course (Time 2) and one year after completion of the RT course (Time 3). Unstimulated and chewing-stimulated whole saliva were collected, and salivary flow rates at the three time points were assessed. The severity of xerostomia was evaluated using the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer (RTOG/EORTC) morbidity score. Mean radiation dose (Gy) to parotid glands was calculated. Descriptive statistics and student’s t-test were used to determine associations between mean dose to parotid glands, changes in saliva flow and xerostomia scores. Results Patients with xerostomia grade 2-3 had received a significantly higher mean RT dose than patients with xerostomia grade 0-1 (p <0.001) (Figure 1a). Unstimulated and chewing-stimulated whole saliva flow rates were lower in patients with xerostomia grade 2-3 than in patients with xerostomia grade 0-1 (p <0.001) (Figure 1b). Mean RT dose correlated positively with xerostomia grades (R 2 =0.79) (Figure 2a). A mean dose above 39 Gy was associated with xerostomia grade 2-3. There was a moderate correlation between salivary flow changes and mean dose for both unstimulated and stimulated saliva at Time 2 and 3 (R 2 = 0.29-0.41) (Figure 2b and 2c). A mean RT dose above 39 Gy was associated with a drop in the unstimulated saliva flow rate of 0.35 ml/min and in the stimulated saliva flow rate of 1.07 ml/min at Time 3. This indicates that at a mean dose above 39 Gy, about one third of the patients with initial unstimulated salivary flow below 0.45 ml/min and stimulated salivary flow below 1.8 ml/min will experience hyposalivation (threshold value 0.1 ml/min for unstimulated and 0.7 ml/min for stimulated saliva), and almost all patients will experience prominent xerostomia of grade 2-3 one year after RT.