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Solid Lead-glass Viewing Windows for High Energy Radiotherapy Installations

Physics Department, Mount Vernon Hospital and The Radium Institute, Northwood, Middlesex

This excerpt was created in the absence of an abstract.

The design of buildings for high energy radiotherapy units requires an early consideration of the means whereby the patient may be kept constantly in the view of the operator during treatment. In the case of two such recent installations at this Centre, the "Theratron" Cobalt 60 unit^* and the "Orthotron" 4 MeV linear accelerator, we have designed and installed direct-vision windows, each of which consists of a single block of high-density lead glass, built into a thick concrete wall separating the treatment and control rooms. The decision to adopt this method of viewing, after a full consideration of alternative schemes, was based on the following considerations:

1. Such windows provide direct vision, their use involving a minimum of effort on the part of the operator, while the apparent distance between patient and operator is not increased. Periscopic methods, on the other hand, necessarily produce an increase in optical path. This may be reduced by the use of either (a) a binocular arrangement at the viewing end, involving, however, rather more effort on the part of the viewer, or (b) spherical mirrors, entailing a considerable increase in cost. Moreover, mirrors of any kind require periodical cleaning.

2. The design of both treatment units is such that the patient, and particularly the region under treatment, will always occupy about the same position relative to the operator, so that the window area can be quite small. Single lead-glass blocks of the required dimensions were available.