Hazards of sparing the ipsilateral parotid gland in the node-positive neck with intensity modulated radiation therapy: Spatial analysis of regional recurrence risk

PURPOSE: The practice of deliberately sparing the ipsilateral parotid gland with intensity modulated radiation therapy (IMRT) in patients with node-positive head and neck cancer is controversial. We sought to compare the clinical outcomes among consecutive cohorts of patients with head and neck cancer who were treated with differing strategies to spare the parotid gland that is ipsilateral to the involved neck using IMRT. METHODS AND MATERIALS: A total of 305 patients were treated with IMRT for node-positive squamous cell carcinoma of the head and neck. The first 139 patients were treated with IMRT whereby the ipsilateral parotid gland was delineated and intentionally designated as an avoidance structure during planning. The subsequent 166 patients were treated by IMRT without the deliberate sparing of the ipsilateral parotid gland. RESULTS: The 2-year estimates of overall survival, local-regional control, and distant metastasis-free survival were 84%, 73%, and 87%, respectively. The 2-year estimates of overall survival were 77% and 86% among patients who were treated by IMRT with and without the sparing of the ipsilateral parotid gland, respectively (P = .01). The respective rates of 2-year regional control were 76% and 90% (P < .001). A trend was observed between increased nodal burden in the ipsilateral cervical neck and the likelihood of regional failure for both groups. A spatial evaluation revealed a significantly higher incidence of marginal failures and true misses in the cohort of patients who underwent IMRT with the sparing of the ipsilateral parotid gland. CONCLUSION: Caution is urged when using IMRT to spare patients' parotid gland on the involved side of neck disease. Our study showed a significantly higher preponderance of regional failure, which highlights the need for careful patient selection and consideration of clinical and pathological factors that influence the likelihood of disease recurrence in the ipsilateral neck.