RecruitingPhase 3Clinical trialSPECT-CT Guided ELEctive Contralateral Neck Treatment for Patients With Lateralized Oropharyngeal CancerThis study is being done to answer the following question: Is the chance of cancer spreading or returning the same if radiotherapy to the neck is guided, by using a special imaging study called lymph node mapping (lymphatic mapping) Single Photon Emission Computed Tomography (SPECT-CT), compared to the usual treatment when radiotherapy is given to both sides of the neck?