General principles of irradiation therapy as applied to head and neck cancer

The general principles of irradiation therapy as applied to head and neck cancer are illustrated by discussion of typical radiation treatment planning for an early glottic carcinoma, carcinoma of the larynx with subglottic extension, a paranasal sinus carcinoma, and a localized tonsillar carcinoma. Each example shows how with modern techniques and careful planning radiation therapy can be directed homogeneously to any desired volume containing tumor but limiting the complications produced in the normal tissues. Homogeneous distribution of the dose of irradiation within the tumor is essential to avoid "cold" spots producing tumor recurrence and "hot" spots producing normal tissue complications. Improvements in technique of irradiation have halved the recurrence rate in T1 glottic cancer and reduced neck node recurrences in T1 supraglottic cancer from 19% to 3%. Techniques of implantation and the concept of therapeutic ratio are also discussed. The concepts of pre vs postoperative irradiation are discussed and the Toronto approach of delayed combined irradiation and surgery, which represents in our view the optimal combination of irradiation and surgery, is reviewed.