The application of automatic computing machines to radiation treatment planning. 1954

A new method of determining the dose distribution required in treatment planning has been developed by using punched cards, and sorting and tabulating machines instead of isodose charts. The percentage depth doses produced by an X-ray field are first recorded on several sets of punched cards. The number of sets required for one field depends upon the distances used from the cross point of the multifield axes to the point of entry. Each set consists of 36 cards, with each card recording the percentage depth doses of 15 points in one radial line, taking the cross points of central axes of the fields as the origin. In all cases the points are taken at the distances 0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 24 cm from the origin and along radial lines 10 deg. apart. A special polar co-ordinate dose distribution sheet has been designed, and the contour of the patient's body and the position of the fields designated for treatment are drawn on this sheet. Instead of putting the isodose charts at the proper positions of the fields, the sets of punched cards for the fields to be applied are automatically arranged in the right order. Instead of the time-consuming process of reading off the percentage depth doses from the overlapping isodose charts and adding them up for selected points, the cards are fed into the automatic tabulating machine, which makes the summation of data for all the points mentioned above and tabulates the results. The whole operation is done in 10 to 15 minutes. The tabulated results are then plotted on the special dose distribution sheet. A generalised mathematical treatment of the dose at any point in the irradiated region is discussed, and an equation of "point-tumour dose ratio" is derived. Further application of this equation is made to special cases for treatment using equal maximum doses, equal tumour doses and rotation therapy. The geometrical principles involved are also indicated.