POTENTIAL RESOLUTION OF A CS-137 COMPUTERIZED TOMOGRAPHIC SCANNER FOR RADIOTHERAPY PLANNING

If (137)Cs is used to delineate cross-sectional tissue structure for radiotherapy treatment planning, avoiding excessive dose to the patient and a source so active that shielding becomes a problem, a spatial resolution of about 0.5 cm may be achieved. This would be adequate for treatment planning, since the position of a contour representing a change in linear attenuation coefficients covering a number of pixels could be defined with a greater accuracy than the 0.5 cm. The effect of inaccuracies in the position of edges and inhomogeneities on tumour and normal tissue dose would be acceptably small. Also, the relative positions of critical organs could be obtained by tomography with an accuracy which would provide treatment plans of greater clinical value than some presently accepted.