Individually Designed Filters in Cobalt 60 Teletherapy

LENNART SUNDBOM It is the general intention when using radiation for therapeutic purposes to give a high and homogeneous dose to a certain body volume.The dose outside this volume, on the other hand, should be as low as possible, and in organs sensitive to radiation this is of extreme importance.Different methods are therefore used in an attempt to control the dose distribution in the body.The use of wedge filters is a move in that direction (COHEN et coll.1960).Isodose diagrams show the effect of such filters although for practical reasons the number of these diagrams has to be limited; this practical limitation is also true, of course, in the case of open beams.The number of diagrams may be reduced by standardizing the conditions in the measurement of the diagrams, e. g. by measuring in a water-equivalent material, by making the surface of the phantom plane and perpendicular to the beam axis, and by using only a limited number of types of wedge filter.This article deals with the possibilities made available by the use of individ-ualIy designed filters to gain independence from the effect of body contour and the position in the body of the treatment volume.The filters are mounted