Beam profiles for x-ray rotation therapy

Determining the beam configuration necessary to deliver a desired dose distribution with rotation therapy is equivalent to solving an integral equation. The equation has been solved analytically for a handful of dose distributions having specific radial variation and either rotational or reflective angular symmetry. In this work a numerical method for calculating beam profiles appropriate for producing distributions having arbitrary radial variation and angular symmetry of order l greater than or equal to 2 is presented. The accuracy of the technique is demonstrated by comparison with one of the few dose distributions for which an analytic solution exists, and the ability to produce both more general and conformal distributions is also shown. The problems of negative intensity and scatter are discussed. (C) 1998 American Association of Physicists in Medicine. [S0094-2405(98)01206-1].