What factors, if any, (such as microscopic ENE (<=2 mm) or larger nodal size (e.g., >4 cm)) would prompt you to treat the contralateral neck for oropharyngeal cancers otherwise eligible for unilateral radiotherapy? 

BOT primary that are not very lateral, as well as tonsillar ca involving the palate, have potential contralateral lymphatics, and contralateral neck RT should be considered.

The ipsilateral RT series in the IMRT era are still small. The classical large OSullivan study included few patients with N2b ...