A method of correction for curvature and inhomogeneities in computer aided calculation of external beam radiation dose distributions

This paper deals with the problem of finding the effective pathlength along a ray passing through a patient's outline and internal structure. The pathlength contributes to the correction applied for curvature and inhomogeneities in the computer-aided calculation of external beam radiation dose distributions. The pathlength is found by first determining the intersections of the ray with the contours defining the patient's body and the interior inhomogeneities. From these intersections the geometric length within each contour is obtained. This information is then employed in a treatment planning program for high energy gamma and X-rays and electrons, in which the radiation dose distribution is computed taking into account the actual inhomogeneous tissue structures. Other applications of the techniques described to problems in the field of radiation therapy are briefly discussed.