A new type of sorting program for plotting of isodose curves

The determination of isoeffect curves (sometimes within given contours) from data given in an n x m matrix is a general scientific problem. The algorithm to be described is useful e.g. for pen plotters not only in the case of brachytherapy but in teletherapy too. It takes into consideration the effect of the body contour (isodose curves are not plotted outside the contour). The points with the desired dose value are rearranged into continuous line segments. The segments are characterized by the serial number of their start point and that of their extremity and by a variable the value of which can be 0 or 1 depending on whether the segment is closed or not. The number of the unconnected segments is the fourth variable characterizing the isodose line. The sorting algorithm ensures the less motion of the pen and the less tests during the plotting process. The algorithm has been implemented on IBM compatible PC's.