Optimisation of conformal radiotherapy dose distributions by simulated annealing

A method of computing the beam profiles for multi-element multiple-beam radiotherapy treatment is presented. This is applicable to the treatment planning of conformal radiotherapy using an isocentric rotation technique. The method begins with the treatment dose prescription and calculates the beam profiles rather than the reverse 'conventional' planning technique. The method is the iterative optimisation method of simulated annealing. It is shown using published 'difficult' clinical treatment planning problems that the high-dose region can be very precisely tailored to the tumour volume even when this has a re-entrant (concave) periphery. Simultaneously the dose can be constrained in other sensitive regions. The mathematics of the method is explained together with this implementation. The analogy of this optimisation with certain reconstruction problems in medical imaging is drawn and by way of experiment dose distributions are presented in image form and beam profiles as sinograms.