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Systems to Ensure the Correct Application of Wedge Filters

Medical Research Council, Betatron Research Unit, Christie Hospital and Holt Radium Institute, Manchester

This excerpt was created in the absence of an abstract.

In a treatment where a wedge filter is used, the dose given may be in error by as much as a factor of two if the wrong wedge is used, or if the correct wedge has its thin end incorrectly orientated with respect to the treatment field. It is, therefore, considered necessary to provide a physical interlock to ensure that the radiotherapists' instructions are correctly carried out. It transpires that the details of such a system depend on whether or not an applicator is used and the two possibilities will be considered separately.

If the treatment to be considered is one where an applicator would normally be used (e.g. a small field, beam-directed treatment at 250 kV), it is usual in this hospital to mount the wedge filter in a special applicator. On the face of this applicator are two pegs. The distance between these is peculiar to the wedge filter in the applicator and the position of the eccentric peg specifies its thin end. If two suitable holes are bored in the wax seating of a patient's beam direction shell, it is then only possible to seat the correct applicator at the correct angle on to it.

In a gantry-mounted X-ray machine (Howard-Flanders and Newbery, 1950), for example the 4 MeV linear accelerator (Miller, 1954), it is not desirable to have a rigid linkage between the patient and the X-ray head.

Received for publication May 1, 1958.