A filtered backprojection dose calculation method for inverse treatment planning.

An efficient method of calculating dose distributions in homogeneous media for megavoltage photons is described. The method is similar to filtered backprojection image reconstruction and is based on the analogy between external beam radiotherapy and SPECT image reconstruction. The filtered backprojection dose calculation significantly reduces the computation time for a large number of x-ray beams compared to a conventional convolution dosimetry method. A factor of 20 reduction in computation time is demonstrated for a 2D implementation of the model. The method has proved useful for speeding up an inverse treatment planning algorithm for conformal radiotherapy, and has the potential to be implemented in the reconstruction hardware of a radiotherapy CT simulator. Results of computer simulations based on the model are presented.