Radiotherapy treatment planning using three dimensional CT images

Recently superimposition of dose distribution onto CT images has become available with the use of planning computers. However, the distribution is mostly along the plane of central axis of the beam, and evaluation of the quality of planning has not been established yet. It cannot be concluded whether the planning is suitable or not, even if the dose distribution at a certain CT slice seems to be optimum. The need has been emerged to compare the treatment planning quantitatively with other ones. A computerized treatment planning system has been developed in our hospital, which can accumulate voxel dose of each lattice point, can superimpose isodose curves on multiple transverse contours, and can construct and display a 3-dimensional image of the treatment region using a ''cutting method''. In this paper, a method is proposed to evaluate the quality of treatment planning, introducing the definitions in ICRU report 29 and using the 3-dimensional computer algorism. Concepts and procedures are described in detail with some case examples. (author)