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.
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