Optimizing beam weights and wedge filters with the concept of the super-omni wedge.

This study introduces a new concept, the super-omni wedge, and proposes an algorithm for optimizing beam weights, wedge angles, and wedge orientations on the basis of this new concept. The super-omni wedge is a generalization of the omni wedge. Instead of combining one open beam and two orthogonal wedged beams, it uses two orthogonal pairs of nominal wedged beams to generate a wedged dose distribution with an arbitrary wedge angle and an arbitrary wedge orientation. The orientations of a pair of nominal wedges are opposite each other. In this way, the effective wedge orientation can vary from 0 degrees to 360 degrees rather than being restricted to one quadrant. When the concept of the super-omni wedge is used, the optimization of beam weights, wedge angles, and wedge orientations for J beams is transformed into the optimization of beam weights for 4J beams. A quadratic dose-based objective function is defined, and the method of sequential quadratic programming is used to find the 4J beam weights that minimize it. After the weights of the nominal wedged beams have been determined, the beams can be delivered in one of four methods: Directly, by using the omni wedge technique, by using the universal wedge technique, and by using the virtual wedge technique. When tested with two clinical cases, the algorithm achieved homogeneous dose distributions in target volumes while meeting the constraints to the organs at risk. A prominent feature of the algorithm is that there is no need to manually preselect the orientations of nominal wedges.

[1]  A T Redpath,et al.  A new technique for radiotherapy planning using quadratic programming. , 1976, Physics in medicine and biology.

[2]  E. Sternick,et al.  Effective wedge angles for 6-MV wedges. , 1985, Medical physics.

[3]  R L Siddon,et al.  Effective wedge angles with a universal wedge. , 1985, Physics in medicine and biology.

[4]  William H. Press,et al.  Numerical recipes in C. The art of scientific computing , 1987 .

[5]  Masao Fukushima,et al.  A successive quadratic programming algorithm with global and superlinear convergence properties , 1986, Math. Program..

[6]  I I Rosen,et al.  Dose-volume considerations with linear programming optimization. , 1991, Medical physics.

[7]  S. Webb.  Optimization by simulated annealing of three-dimensional, conformal treatment planning for radiation fields defined by a multileaf collimator: II. Inclusion of two-dimensional modulation of the x-ray intensity. , 1992, Physics in medicine and biology.

[8]  R Mohan,et al.  Application of fast simulated annealing to optimization of conformal radiation treatments. , 1993, Medical physics.

[9]  G. Sherouse.  A mathematical basis for selection of wedge angle and orientation. , 1993, Medical physics.

[10]  A. Brahme,et al.  A generalized pencil beam algorithm for optimization of radiation therapy. , 1994, Medical physics.

[11]  S Morgan-Fletcher,et al.  How can the co-ordinate transformation method of beam matching be extended to include separately labelled collimators? , 1996, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[12]  R. Hamilton,et al.  The omni wedge: a method to produce wedged fields at arbitrary orientations. , 1996, Medical physics.

[13]  R. Lane,et al.  A generic genetic algorithm for generating beam weights. , 1996, Medical physics.

[14]  C. Pelizzari,et al.  Optimization of relative weights and wedge angles in treatment planning. , 1997, Medical physics.

[15]  J W Wong,et al.  Verification of the omni wedge technique. , 1998, Medical physics.

[16]  C. Pelizzari,et al.  A three-dimensional algorithm for optimizing beam weights and wedge filters. , 1998, Medical physics.

[17]  S. Spirou,et al.  A gradient inverse planning algorithm with dose-volume constraints. , 1998, Medical physics.

[18]  A L Boyer,et al.  Clinical implementation of wedge filter optimization in three-dimensional radiotherapy treatment planning. , 1999, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.