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

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Abstract
The possible influence of the structure and anatomical relationships of the pharynx on the spread and radio-sensitivity of its tumors is discussed. The technique of treating pharyngeal tumors by telecobalt therapy, with special reference to the nasopharynx, is described. For squamous carcinomata of the nasopharynx, a 3-phase treatment plan is indicated, in which the primary receives 6,000 rads in 6 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 7 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 was derived from experimental data for 70 cm source-surface distance (SSD) split fields, which enables the central penumbral iso-dose separations 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 conjuction with anterior split fields.

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