Enhanced bremsstrahlung spectrum reconstruction from depth-dose gradients.

We present a technique to significantly improve the accuracy of bremsstrahlung spectra reconstructed from central-axis depth-dose data using inverse methods. While typical approaches directly use the measured depth-dose data, we show the advantage of using the gradient of these data for reconstruction. The inverse problem in terms of gradients is shown to be markedly less ill-conditioned than the usual inverse problem. In each case, a regularization is introduced to alleviate the effects of noise due to measurement and computation. The error in taking derivatives of depth-dose data is demonstrated to be sufficiently controllable as not to overtake the improvements in the conditioning of the inverse problem in a pair of simulated examples.