Characterization of an x-ray source with a partitioned diamond-tungsten target for electronic brachytherapy with 3D beam directionality

Design and optimization of thin-film tungsten (W)-diamond target for multi-pixel X-ray sources

BACKGROUND

Emerging multi-pixel X-ray source technology enables new designs for X-ray imaging systems. The power of multi-pixel X-ray sources with a fixed anode is limited by focal spot power density.

PURPOSE

The purpose of this study is to optimize the W-diamond target and predict its performance in multi-pixel X-ray sources.

METHODS

X-ray intensity and energy deposition in the W-diamond target with different thicknesses of tungsten film and incident electron energies was calculated with the Geant4 Monte Carlo toolkit. COMSOL Multiphysics software was used to analyze the transient and stationary heat transfer in the thin-film W-diamond target. The maximum tube power and X-ray output intensity were predicted for both transmission and reflection target configurations.

RESULTS

The maximum focal spot power density was limited by either the graphitization of the diamond substrate or the melting point of the W target. With optimal W-target thickness, the maximum transmission X-ray intensities are about 40%-50% higher than the maximum reflection intensities. Thin-film W-diamond targets allow four to five times more maximum power input and produce six to seven times higher transmission X-ray intensity in continuous mode compared with conventional reflection W thick targets. Depending on the focal spot size, reducing the X-ray pulse duration can further enhance the tube power.

CONCLUSIONS

Multi-pixel X-ray sources using this W-diamond target design can produce significantly higher X-ray output than traditional thick tungsten targets without major modification of the tube design.

Inverse treatment planning for an electronic brachytherapy system delivering anisotropic radiation therapy

An inverse radiation treatment planning algorithm for Sensus Healthcare's Sculptura^TM electronic brachytherapy system has been designed. The algorithm makes use of simulated annealing to optimize the conformation number (CN) of the treatment plan. The highly anisotropic dose distributions produced by the Sculptura^TM x-ray source empower the inverse treatment planning algorithm to achieve highly conformal treatment plans for a wide range of prescribed planning target volumes. Over a set of 10 datasets the algorithm achieved an average CN of 0.79 ± 0.08 and an average gamma passing rate of 0.90 ± 0.10 at 5%/5 mm. A regularization term that encouraged short treatment plans was used, and it was found that the total treatment time could be reduced by 20% with only a nominal reduction in the CN and gamma passing rate. It was also found that downsampling the voxelized volume (from 320³ to 64³ voxels) prior to optimization resulted in a 150× speedup in the optimization time (from 2 + minutes to < 1 s) without affecting the quality of the treatment plan.