Beam definition on superficial and orthovoltage machines is achieved using solid walled applicators; these are available in a range of square, rectangular and circular sizes and FSD’s, thus allowing greater flexibility in treating a wide range of conditions.
However, on occasion it may be necessary to further define the treatment field from the size of the applicator chosen. Such occasions may include situations where a field size is required within the predefined applicator size or the shape of the field is irregular. In such cases a lead cut out is used [2].

 

A sheet of lead of varying thickness (mm), depending on the energy range, is used to define the size and shape of the field. The lead cut out is placed on the patient’s skin (secured with medical tape) and the treatment is set up as normal using an applicator to achieve apposition with the cut out.

Lead cut outs are used, not only to define the shape of the beam, but also to protect the surrounding normal tissue from exposure to X-Rays.
Depending on the treatment area, further shielding to protect normal tissues may be required. For treatment in close proximity to the eye, an external eye shield may be required. Eye shields are oval shaped pieces (see below) of lead which are placed over the patients closed eye to protect the lens from unnecessary irradiation.

If the eyelid itself is being treated it is necessary to use an internal or contact eye shield to protect the eye. This is an oval shaped, concaved gold eye shield with a protective lead lining. The eye shield is placed in the patients’ eye, like a contact lens, between the cornea and the eyelid. This procedure is carried out following the use of local anaesthetic to the eye, which stops the blink reflex, thus allowing for insertion of the eye shield. It is important that patients be cared for properly following this procedure. A protective eye patch should be used until the blink reflex returns [1] to normal.

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