AbstractID: 9047 Title: Dose-distance constraints: A new method for controlling intensity modulated treatment planning dose distributions
Intensity modulated radiation therapy treatment planning (IMRTP) potentially provides detailed control over radiation doses on a voxel-by-voxel basis. However, current methods do not allow a user to specify which voxels should get which doses except insofar as they are lumped together in objective function terms. We propose a new method of controlling the spatial ‘encroachment’ or ‘expulsion’ of high dose regions near targets or normal structures in IMRTP. ‘Dose-distance constraints’ are defined as voxel dose limit constraints based on each voxel’s closest distance to one or more nearby structures. They are included as hard constraints during optimization. For example, a planner might apply a dose-distance constraint to increase dose to all the voxels within 1 cm of a target boundary. Dose-distance constraints can be used to control the encroachment of high dose regions near normal structures. Priorities can be defined between targets or normal tissues so that ‘conformal avoidance’ can be controlled. Dosedistance constraints can be used to approximately implement dose-volume constraints by constraining only those voxels farthest from the target, thereby allowing voxels near the target to rise to higher doses. Because dose-distance constraints are linear, fast linearquadratic solvers can be applied. Examples are given of dose-distance constraints to precisely control the position and shape of the high-dose gradient in IMRTP in relation to the surrounding structures.
Supported by CMS, Inc., and NIH grant R29-CA85181.