The goal of sophisticated treatment planning in radiation therapy is to maximize dose to the tumor or target volume, while the integral dose is minimized, to reduce normal tissue morbidity. In the head and neck regions, the anatomic irregularities of individual patients and the critical structures that limit the administration of dose within the irradiated volumes often complicate the optimization of dosimetry. The availability of dual-energy accelerators that deliver beams of low- and high-energy photons allows the convenient administration of mixed-energy photon irradiation and facilitates the development of optimal treatment strategies for selected lesions. Highly lateralized carcinomas of the upper aerodigestive tract, in which sparing of contralateral cervicofascial tissue is desirable, are particularly well suited for this technique. Treatment plans that make use of irradiation with conventional single-energy beams and mixed-energy photon therapy are compared for representative lesions of the head and neck.