Radiation treatment of cancer of the pharynx: with special reference to telecobalt therapy

The possible influence of the structure and anatomical relationships of the pharynx on the spread and radiosensitivity of its tumours is discussed. The technique of treating pharyngeal tumours by telecobalt therapy, with special reference to the nasopharynx, is described. For squamous carcinomata of the nasopharynx, a three-phase treatment plan is indicated, in which the primary receives 6,000 rads in six weeks during phases I and II, and the lymph nodes 4,800–5,400 rads. In phase III the primary receives a further 1,000 rads, and supplementary radiation is given to palpable lymph nodes so that they receive at least a dose of 7,000 rads in a minimum of seven weeks. The necessity and indications of the use of a split field in the treatment of cervical lymph node areas are described in detail. A formula has been derived from experimental data for 70 cm. SSD split fields, which enables the central penumbral isodose separation to be calculated as a function of shield width and depth below skin surface. (Telecobalt source size: 1·7 cm diameter; Distance from source to nearest surface of shield: 49 cm). An account is also given of the post-radiation complications that may occur and methods for their prevention. Protective devices to shield cornea, globe and orbit are described, together with a segmented shield with a tapered cross-section which is used in conjunction with anterior split fields.