Calculation of Tissue Doses and Data for the Production of Isodose Charts, Using Standard Depth-Dose Tables

For satisfactory dosage planning in radiotherapy, isodose charts are essential. Data for such charts can be obtained by measurements in unit-density phantoms, using suitable small ionization chambers, but this is a tedious procedure, with many possibilities for error. Many departments, therefore, prefer to use charts available through data exchange schemes such as the one operated by the British Hospital Physicists' Association, or by one or two groups in the United States. This is not entirely satisfactory, since it is seldom possible to obtain curves for all field shapes and radiation qualities desired, and adaptation is rather hazardous. On the other hand, the calculation of such data from available central-axis depth-dose tables is practicable, and several methods have been developed for the procedure (1, 4, 6-10). None of these has been widely employed in the United States, either because of lack of familiarity with them, or because the work involved seemed too great. The basis for the calculation is...