Elective nodal dose of 60 Gy or 50 Gy in head and neck cancers: A matched pair analysis of outcomes and toxicity

Purpose: The main objective of this study was to evaluate appropriate doses for elective nodal irradiation (ENI) in head and neck squamous cell carcinoma (HNSCC) patients to optimize the therapeutic ratio. Methods and materials: A matched pair analysis of 2 similar cohorts of HNSCC treated with intensity modulated radiation therapy with different dose prescriptions to the elective nodal regions was conducted. One group received 60 Gy, whereas the other received 50 Gy (ENI60 and ENI50 groups, respectively). Isolated regional recurrences (IRR) and locoregional control were evaluated. Doses received by the parotid and thyroid glands were compared among both groups and were clinically correlated with the trend of salivary function recovery and incidence of hypothyroidism. Results: Of the 110 patients studied, 97 were eligible for analysis after matching based on propensity scores. The 3-year locoregional control rate was similar in ENI60 and ENI50 (78.7% and 77%, respectively; P = .93). There were no IRR in ENI regions in either group. The mean ipsilateral parotid dose in ENI60 was significantly higher compared with ENI50 (42 vs 35.7 Gy, P = .03). There was no significant difference in the mean contralateral parotid doses (32.5 vs 31.7 Gy, P = .6). The mean thyroid doses were high in ENI60 compared with ENI50 (54.7 vs 43.3 Gy, P < .001). A significant difference in ipsilateral parotid salivary excretory fraction ratio at 1 year (P = .03) was observed with quicker recovery of salivary function. The salivary excretory fractions were poorer in the ENI60 group with higher mean parotid doses (P = .009). At 2 years, 26 patients (54%) in the ENI60 group and 13 patients (26.5%) in the ENI50 group developed biochemical hypothyroidism (P = .007). Conclusions: Doses of 50 Gy equivalent are sufficient to sterilize the uninvolved nodal regions because the rates of IRR are extremely low. Using ENI50 results in clinically meaningful reduction in salivary and thyroid toxicity in HNSCC.