Three-Dimensional Solution of the Inverse Problem in Conformation Radiotherapy

Several recently published papers deal with the so-called inverse problem of radiation therapy (Brahme 1988; Webb 1989; Barth 1990; Goitein 1990; Lind and Kallman 1990; Bortfeld et al. 1990a). Most of the authors define this as the problem of directly determining treatment parameters on the basis of the desired dose distribution, which is the inverse process to that in conventional radiotherapy planning. Usually, the term inverse problem is used in conjunction with a new treatment technique using modulated irradiation fields, where the treatment parameters are the modulation profiles for each beam direction. Also, in this context, the term inverse problem is justified because the problem of calculating the modulation profiles is in principle a matrix inversion problem.