The Jacobian as a measure of planar dose congruence.

We propose a new starting point for comparing planar dose distributions using a Jacobian-based measure. The measure is normalization independent, i.e.

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.

Spectral sensitivity study of dose distributions for a commercial convolution/superposition algorithm.

The focus of this study is to validate whether the sensitivity of dose distribution following the interface of different media can be used to distinguish between small variations of photon energy spectra in the context of the convolution/superposition algorithm in the polyenergetic implementation (Philips Pinnacle3, ADAC Laboratories, Milpitas, CA). Calculations were performed in homogeneous water and heterogeneous lung/water phantoms. Spectra were generated, in which the weights of the low-, medium- and high-energy components were adjusted sequentially.

Enhanced spectral discrimination through the exploitation of interface effects in photon dose data.

The convolution/superposition algorithm for computing dose from photon beams in radiation therapy planning requires knowledge of the energy spectrum. The algorithm can compute the dose for a polyenergetic beam as the weighted sum of the individual dose contributions from monoenergetic beams. In this study we exploit interface effects apparent in the dose distributions to discriminate among spectra of high energy photon beams.

Matrix theory interpretation of discrete light cone quantization string worldsheets.

We study the null compactification of type-IIA string perturbation theory at finite temperature. We prove a theorem about Riemann surfaces establishing that the moduli spaces of infinite-momentum-frame superstring worldsheets are identical to those of branched-cover instantons in the matrix-string model conjectured to describe M theory. This means that the identification of string degrees of freedom in the matrix model proposed by Dijkgraaf, Verlinde, and Verlinde is correct and that its natural generalization produces the moduli space of Riemann surfaces at all orders in the genus expansion.