Evaluation of bremsstrahlung spectra generated by a 4‐MeV linear accelerator

Abstract

A modified method for the evaluation of bremsstrahlung spectra on the basis of transmission measurements is presented. The method is tested for two 4 MeV therapy accelerators. The calculated spectra are compared with other experimental results and Monte Carlo simulation.

Comparison between measured and predicted attenuation curves of x-ray beams

“…The finding of functional relations between Cu and Al with an explicit inverse Laplace transform of its negative exponential in an energy range higher and wider than the one used here will allow us to extend this kind of description of the penetration properties to therapy photon beams which are described by attenuation measurements. 15…”

An improved physics-based approach for unfolding megavoltage bremsstrahlung spectra using transmission analysis

“…In previous transmission analysis studies, the ion-chamber energy response was roughly approximated by one of the following three methods: (1) assuming that the material of the chamber wall and buildup cap are air-equivalent, thus the aircavity dose, D cav , equals the collision air-kerma, K air col , and consequently, R(d, E) is proportional to ðl en =qÞ air , the mass energy absorption coefficient for air; 16,17,23,24,26,31,32 (2) measuring the response at a few known low energies (e.g., 137 Cs and 60 Co) then interpolating or extrapolating to other energies; [4][5][6][11][12][13] or, (3) developing approximate expressions to take into account the deviation from air equivalence caused by the wall and/or cap materials. 8,14,27 To the authors' knowledge, no previous study on transmission analysis used Monte Carlo for detailed detector modeling.…”

“…Answers to this question include the methods of Laplace transform pairs, [4][5][6] direct matrix inversion, 7,8 neural networks, 9 and iterative unfolding (including least-squares, expectationmaximization, and simulated annealing) with: (a) a priori spectral knowledge and smoothing constraints, [10][11][12][13][14][15][16][17] (b) regularization, [18][19][20][21] or (c) spectrum parameterization. [22][23][24][25][26][27][28][29][30][31][32][33] In this study, before approaching the unfolding issue, we first try to answer the more fundamental question: how can we make the transmission data themselves contain more (and accurate) spectral information? To this end, EGSnrc (Refs.…”

Application of an expectation maximization method to the reconstruction of X-ray-tube spectra from transmission data

“…Information about this distribution is recovered by using a series of attenuation measurements in which the spectrum is progressively modified by varying the filtration. A number of different approaches have been proposed for the solution of this problem, including the use of the Laplace transform, least squares methods, singular value decomposition and iterative approaches [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. In this work we focus on the application to experimental data of the expectation-maximization method [14,17] to iteratively solve the ill-conditioned linear system that relates the spectral distribution of the X-ray beam to its transmission.…”