Correlating parotid dose with xerostomia in whole-brain irradiation: A prospective observational study

ABSTRACT Background: Whole-brain radiotherapy (WBRT) remains a mainstay treatment for brain metastasis despite increasing usage of stereotactic radiosurgery. Although parotid glands receive substantial radiation during WBRT, they are not routinely considered organs at risk, and dosimetric data are often unreported. Objectives: The primary objective was to assess xerostomia in WBRT patients; the secondary objective was to correlate xerostomia with parotid gland radiation dose. Materials and Methods: This prospective, observational study included adult patients with confirmed brain metastasis treated with 3-dimensional (3D) conformal WBRT at Father Muller Medical College Hospital, Bangalore between April 2023 and April 2024. Parotids were retrospectively delineated, and dose-volume parameters were recorded. Xerostomia was assessed using the University of Michigan xerostomia questionnaire at baseline, end of RT, 1 month, and 3 months post-RT. Results: We included 22 patients in the study (mean age: 53.5 ± 9.2 years), with a female predominance. Breast ( n = 12, 54.5%) and lung ( n = 7, 31.8%) cancers were the most common primaries. The mean parotid dose was 17.6 Gy; the median V20 was 16.7%. Xerostomia scores increased significantly post-RT, with an 18-point mean rise ( P < 0.001). Nine patients (40.9%) experienced a ≥20-point increase, indicating toxicity. A strong correlation was found between V20 and xerostomia severity ( P < 0.001). Conclusion: Xerostomia is a common yet underreported side effect of WBRT, significantly associated with parotid dose. To preserve quality of life, parotid glands should be delineated, and their radiation exposure minimized during WBRT planning.