Proof‐of‐concept for a thin conical X‐ray target optimized for intensity and directionality for use in a carbon nanotube‐based compact X‐ray tube

Abstract

BackgroundCarbon nanotube‐based cold cathode technology has revolutionized the miniaturization of X‐ray tubes. However, current applications of these devices required optimization for large, uniform fields with low intensity.PurposeThis work investigated the feasibility and radiological characteristics of a novel conical X‐ray target optimized for high intensity and high directionality to be used in a compact X‐ray tube.MethodsThe proposed device uses an ultrathin, conical tungsten‐diamond target that exhibits significant heat loading while maintaining a small focal spot size and promoting forward‐directedness of the X‐ray field through preferential attenuation of oblique‐angled photons. The electrostatic and thermal properties of the theoretical tube were calculated and analyzed using COMSOL Multiphysics software. The production, transport, and calculation of radiological properties associated with the resultant X‐ray field were performed using the Geant4 toolkit via its wrapper, TOPAS.ResultsHeat transfer analysis of this X‐ray tube demonstrated the feasibility of a 200‐kV electron beam bombarding the proposed target at a maximum current of 100 mA using a 1‐ms symmetric duty cycle. The cathode of the X‐ray tube was designed to be segmented into nine switchable electrical segments for modulation of the focal spot size from 0.4‐ to 10.8‐mm. After importing the COMSOL‐derived electron beam into TOPAS for X‐ray production simulations, radiological analysis of the resultant field demonstrated high levels of intrinsic beam collimation while maintaining high intensity. A maximum dose rate of 17,887 cGy/min was calculated for 1‐mm depth in water at 7‐cm distance.ConclusionsThe proposed X‐ray tube design can create highly directional X‐ray fields with superior fluence compared to that of current commercial X‐ray tubes of comparable size.

Numerical optimization of longitudinal collimator geometry for novel x-ray field

“…As the field of radiotherapy explores new realms of treatment, including ultra-high dose rate therapy, microbeam therapy, spatially fractionated radiotherapy, and highly conformal stereotactic radiosurgery (Zhang and Mayr 2023), there is a greater demand for increasingly complex radiation sources and beam shaping devices in the clinical and preclinical spaces (Insley et al 2024). Traditional wisdom on x-ray source design has been upended by the advent of exciting technologies such as field emission carbon nanotube sources, x-ray tube miniaturization, complex target design (Insley et al 2024), x-ray focusing lenses (Bartkoski et al 2021), and beyond.…”

“…As the field of radiotherapy explores new realms of treatment, including ultra-high dose rate therapy, microbeam therapy, spatially fractionated radiotherapy, and highly conformal stereotactic radiosurgery (Zhang and Mayr 2023), there is a greater demand for increasingly complex radiation sources and beam shaping devices in the clinical and preclinical spaces (Insley et al 2024). Traditional wisdom on x-ray source design has been upended by the advent of exciting technologies such as field emission carbon nanotube sources, x-ray tube miniaturization, complex target design (Insley et al 2024), x-ray focusing lenses (Bartkoski et al 2021), and beyond. With the implementation of novel sources into clinical practice, it has become clear that if the x-ray source deviates from conventional design principles, then the construction of other necessary accessory devices, including dosimetry tools, positioning apparatuses, and collimating structures, should be reassessed (Yin et al 2010).…”

“…Toward such an effort, a proof-of-concept analysis has been described in the literature for a novel conical target geometry optimized for high intensity and high directionality (Insley et al 2024). This nontraditional target features a 1.5 mm thick tungsten layer printed on a 1 mm thick conical diamond substrate with a 10°cone semi-angle and a 6 mm base radius.…”

“…To modulate the x-ray field's intensity and focal spot size, the annular surface of carbon nanotubes used to generate the electron beam is segmented into concentric rings. Independent electrical switching of each ring adjusts the size of the electron bombardment area on the target (Insley et al 2024). Some of the main components of this tube are displayed in the upper half of figure 1 along with exemplary electron trajectories shown by semitransparent yellow arrows.…”

“…We then describe a simulated annealing approach to optimize the collimator geometry. Finally, this approach is applied to the novel radiation source described previously (Insley et al 2024).…”