| Abstrakt: |
Many radiotherapy centres are now using stepped compensators of the Ellis type (Ellis, Oliver and Hall, 1959) placed some distance from the skin within the axis of the beam of radiation in order to reduce the amount of scattered secondary radiation absorption on the surface. These tissue compensators are constructed of various materials, usually metal of suitable density such as brass, aluminium or lead.Working in a centre that favours wax compensators, used either directly on the surface of a treatment mould where maximum skin dose is required, or retracted a distance of 5 cm when some degree of skin sparing is desirable, it seemed logical to aim for further reduction of surface absorption by making reduced wax compensators (Fig. 1) that could be placed higher in the radiation beam; the reduction is in the area perpendicular to the central axis of the beam.The intention was to make a simple jig that would facilitate direct construction of compensators as opposed to the more complicated indirect methods available. To make a reduced copy of a three-dimensional curved surface instead of the more typical stepped compensator at first seemed a formidable task. However, the solution was simple.Figure 2 shows the main components of the jig which consists of two thin, rigid, plastic sheets held 10 cm apart in a rigid frame through which holes were drilled to accommodate thin metal pins (No. 14 stainless steel knitting needles). |
