Defining high-risk elective contralateral neck radiation volumes for oropharynx cancer.

BACKGROUND To define the location of the initial contralateral lymph node (LN) metastasis in patients with oropharynx cancer. METHODS The location of the LN centroids from patients with oropharynx cancer and a single radiographically positive contralateral LN was defined. A clinical target volume (CTV) inclusive of all LN centroids was created, and its impact on dose to organs at risk was assessed. RESULTS We identified 55 patients of which 49/55 had a single contralateral LN in level IIA, 4/55 in level III, 1/55 in level IIB, and 1/55 in the retropharynx. Mean radiation dose to the contralateral parotid gland was 15.1 and 21.0 Gy, (p <0.001) using the modeled high-risk elective CTV and a consensus CTV, respectively. CONCLUSIONS We present a systematic approach for identifying the contralateral nodal regions at highest risk of harboring subclinical disease in patients with oropharynx cancer that warrants prospective clinical study.