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Protection Devices for Use with Beam Therapy Units which Involve Pneumatic Transfer of the Radiation Source

Physics Department, Westminster Hospital, London, S.W.1

This excerpt was created in the absence of an abstract.

In the use of beam units which incorporate pneumatic transfer of the source between storage safe and treatment head (Grimmett, 1937; Wilson, 1945; Spiers, 1952) the possibility of the source failing to transfer normally is a source of danger. Such failure may only be apparent and not real if the cause is a defect of the relay circuitry associated with the warning light system. If real, it might be due to lodgement of the source in either the safe or the head, or in the unscreened pipe which conveys the source between the two. From the viewpoint of protection when dealing with such an emergency, the action taken depends upon the position of the source; but without some method of indicating this position, it is not possible immediately to be aware of the exact circumstances.

It is our experience that this kind of emergency occurs only very infrequently (twice in five years), but discussion with others using similar apparatus leads us to think that we may have been fortunate. The chief information that is required as quickly as possible is whether the source is located in the unscreened connecting pipe. Using an ionization chamber detector it proved easy to improvise a method of supplying this information which was considered adequate for sources up to 10 g of radium. Use of considerably more active ₆₀Co sources makes more permanent methods and apparatus desirable in order that incidental exposure of personnel may be minimal.