FAST ITERATIVE ALGORITHMS FOR 3-DIMENSIONAL INVERSE TREATMENT PLANNING

Three types of iterative algorithms, algebraic inverse treatment plann ing (AITP), simultaneous iterative inverse treatment planning (SIITP), and iterative least-square inverse treatment planning (ILSITP), diffe rentiated according to their updating sequences, were generalized to t hree dimension with true beam geometry and dose model. A rapid ray-tra cing approach was developed to optimize the primary beam components. I nstead of recalculating the dose matrix at each iteration, the dose di stribution was generated by scaling up or down the dose matrix element s of the previous iteration. This significantly increased the calculat ion speed. The iterative algorithms started with an initial intensity profile for each beam, specified by a two-dimensional pixel beam map o f M elements. The calculation volume was divided into N voxels, and th e calculation was done by repeatedly comparing the calculated and desi red doses and adjusting the values of the beam map elements to minimiz e an objective function. In AITP, the iteration is performed voxel by voxel. For each voxel, the dose discrepancy was evaluated and the cont ributing pencil beams were updated. In ILSITP and SIITP, the iteration proceeded pencil beam by pencil beam instead of voxel by voxel. In al l cases, the iteration procedure was repeated until the best possible dose distribution was achieved. The algorithms were applied to two exa mples and the results showed that the iterative techniques were able t o produce superior isodose distributions. (C) 1998 American Associatio n of Physicists in Medicine. [S0094-2405(98)01210-3].