Anode optimization for miniature electronic brachytherapy X-ray sources using Monte Carlo and computational fluid dynamic codes

Abstract

A miniature X-ray source has been optimized for electronic brachytherapy. The cooling fluid for this device is water. Unlike the radionuclide brachytherapy sources, this source is able to operate at variable voltages and currents to match the dose with the tumor depth. First, Monte Carlo (MC) optimization was performed on the tungsten target-buffer thickness layers versus energy such that the minimum X-ray attenuation occurred. Second optimization was done on the selection of the anode shape based on the Monte Carlo in water TG-43U1 anisotropy function. This optimization was carried out to get the dose anisotropy functions closer to unity at any angle from 0° to 170°. Three anode shapes including cylindrical, spherical, and conical were considered. Moreover, by Computational Fluid Dynamic (CFD) code the optimal target-buffer shape and different nozzle shapes for electronic brachytherapy were evaluated. The characterization criteria of the CFD were the minimum temperature on the anode shape, cooling water, and pressure loss from inlet to outlet. The optimal anode was conical in shape with a conical nozzle. Finally, the TG-43U1 parameters of the optimal source were compared with the literature.

Dose‐rate considerations for the INTRABEAM electronic brachytherapy system: Report from the American Association of Physicists in Medicine task group no. 292

“…The INTRABEAM system is a fully integrated miniature x‐ray tube system designed for intraoperative radiation therapy. Accelerated electrons drift down an evacuated hollow cylinder (100 mm in length) to strike a thin gold target supported by a beryllium thermal buffer 11 . It is the bremsstrahlung and fluorescent photons produced in this gold target that are used for brachytherapy.…”

“…Accelerated electrons drift down an evacuated hollow cylinder (100 mm in length) to strike a thin gold target supported by a beryllium thermal buffer. 11 It is the bremsstrahlung and fluorescent photons produced in this gold target that are used for brachytherapy. The INTRA-BEAM system is designed to accommodate a variety of applicators that attach to the treatment unit and surround the end of the x-ray tube, providing a selection of dose distributions for treatment.…”

Simulation evaluation of NIST air‐kerma rate calibration standard for electronic brachytherapy

“…25 As the W-alloy coating thickness is near that which maximally produces bremsstrahlung x-rays (results not shown), coating thicknesses in this range would alter the tube output by about 1%, which was similar to that observed by others. 26,27 Tube output changed inversely with anode thickness in the range of 0.356 mm. Assuming a normal distribution with a standard deviation of 0.1 µm for the coating thickness uncertainty and a rectangular distribution for measured anode thickness uncertainty, 25 a Type B standard uncertainty of 5.4% was assigned for derivation oḟ K air (d = 50 cm).…”