A unified approach to the optimization of brachytherapy and external beam dosimetry

Semi-automated optimization of dose distributions is possible using techniques borrowed from imaging science. The ideal distribution of dose is first deconvolved by a convolution kernel yielding an ideal weighting distribution in the patient. The weighting distribution describes the total energy released per unit mass of the irradiated medium. For internal and external radiation sources, this is directly related to the amount and distribution of radioactivity and energy fluence in the medium, respectively. For external sources, the exponential Radon transform is used to obtain ideal fluence projections incident on the patient. In both instances negative values are produced, which when set to zero result in perturbed dose distributions. This may necessitate iterative techniques to reduce the 'residual dose' produced by the zeroing process. Application of the approach is presented for the optimization of 2-dimensional dose distributions in external beam therapy, radioimmunotherapy, and brachytherapy sources.