Safety of differential radiation dosing in lymph node positive necks treated with IMRT

When treating head and neck squamous cell carcinoma (HNSCC) with intensity modulated radiation therapy (IMRT), it is common to use several dose levels for a lymph node positive neck: full dose (66-70 Gy) to gross cancer, intermediate dose (59-63 Gy) to higher risk neck regions, and standard dose (50-54 Gy) to lower risk neck regions. There is no consensus regarding how much of the neck should receive intermediate versus standard dose, however.

HNSCC patients treated with IMRT were identified from 2 academic medical centers between 2004 and 2016. Intermediate dose was restricted to a region of the neck 2 cm above and below the most superior and inferior involved lymph nodes; standard dose was delivered to more distal neck regions. Descriptive statistics were calculated for demographics and clinical characteristics as well as proportions for failures 2 years after treatment. Failure outside the intermediate dose region was determined by calculating confidence intervals from a modification of the Poisson distribution.

Of the 57 necks included in this study, 17.5% experienced disease recurrence in the neck within 2 years of completing treatment. All failures were within the 2-cm margin above or below the most superior and inferior involved nodes; there were no failures outside this 2-cm margin (95% confidence interval, 0-7.7).

The results of this study support the feasibility of treating only the neck adjacent to gross neck disease to an intermediate dose, and treating the remainder of the neck to a lower, standard dose. Although these results are encouraging, additional study of this treatment paradigm is warranted.