Monte Carlo simulation of a miniature, radiosurgery x-ray tube using the ITS 3.0 coupled electron-photon transport code

Abstract

A miniature, interstitial x-ray generator has recently been developed and is currently undergoing clinical trials for the treatment of brain tumors. The maximum photon energy from this x-ray tube is 50 keV, although most of the initial testing has been carried out at 40 keV. Dose rates of up to 2 Gy/min in a water phantom at a distance of 10 mm from the tube tip are produced. In this paper we describe the modeling and simulation of x-ray production from this device using the ITS 3.0 Monte Carlo code. Verification of the simulation of x-ray production in the device was carried out by comparing predictions of spatial photon distribution, energy spectrum, and dose versus depth in water with experimentally obtained measurements. Agreement between the simulated results and experimental measurements was fairly good when comparing the angular distribution of photons emitted from the x-ray tube and very good when comparing dose rate versus depth in a water phantom. Discrepancies observed when comparing the calculated and measured estimates of characteristic line radiation were reduced by incorporation of a modification to the ITS code. Possible causes of the remaining discrepancy in bremsstrahlung intensity are discussed.

Calculated and measured brachytherapy dosimetry parameters in water for the Xoft Axxent X‐Ray Source: An electronic brachytherapy sourcea)

“…Upon comparing the 40 kV Source spectra with 40 kV INTRABEAM™ spectra published in Fig. 3 by Yanch and Harte, 11 it is evident that the higher-energy photon distributions are similar. Differences in lower-energy photon distributions arise from differences in the target materials.…”

“…[6][7][8] X rays are generated in the PRS by a 50 keV electron beam focused from a conventional miniature electron gun onto the tip of a 3-mm-diam rigid drift tube. [9][10][11] The tip of the drift tube comprises a beryllium tube with hemispherical x-ray window coated on the inside with a thin Au target and on the outside with thin nickel and titanium nitride films for biocompatibility. The electron beam is positioned in the center of the hemispherical Be window using a static magnetic deflection system.…”

Technical Note: Effect of explicit M and N‐shell atomic transitions on a low‐energy x‐ray source

“…Source geometry and material specifications were taken from the literature. 7,8 The emitted photon fluence spectra were calculated with the user code cavity. Fluence was scored across a circle of 1 cm diameter, situated 1 cm from the tip along the longitudinal axis of the source.…”

Monte-Carlo dosimetry for intraoperative radiotherapy using a low energy x-ray source

“…Depending on the clinical application, various applicator types can be attached to the XRs. spherical applicators made of polyetherimide material (15-50 mm) are used to deliver radiation to the tumor bed [6][7][8][9].…”