AN OPTIMIZED FORWARD-PLANNING TECHNIQUE FOR INTENSITY MODULATED TREATMENT OF PROSTATE CANCER
Ying Xiao, Richard K. Valicenti, James M. Galvin

Department of Radiation Oncology, Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson University Hospital, Philadelphia, PA

Materials and Methods:
Initially one applies conventional treatment planning techniques and chooses the appropriate beam orientations. For prostate cases treated in our department, a six-field plan (gantry angles of 45, 90, 135, 225, 270, and 315 degrees) is used. To illustrate the proposed technique, cases where the rectum caused a concavity in the prostate surface were selected, and an additional gantry position at 0 degrees was added to provide more options for the dose optimization. For each beam angle, the portal was divided into two segments. One portal conformed to the projection of the prostate with margin, while the second portal provided blocking of the rectum with margin. (These fields in combination can also be thought of as a conformal field plus two boost fields positioned to either side of the rectum.) If more critical structures are involved, extra fields must be added. Upper and lower dose limits are prescribed for the prostate and the critical organ(s). An in-house software package was developed to extract contour and dose information from the CMS/FOCUS planning system for use in the optimization process. This known data and the as yet unknown parameters are combined in a set of inequality functions containing dose for a certain point, be it inside the tumor or the critical organ. The inequalities are solved subject to the constraint that the doses lie between the prescribed lower and upper limits. Cimmino’s simultaneous projection method is used for the optimization process.