Operational characteristics of a prototype x-ray needledevice

Abstract

A prototype x-ray needle, which emits 62.5 kVp x-rays at the tip of a 20 cmlong, 4 mm diameter steel needle, has been developed by Titan Pulse SciencesIncorporated (PSI) (Albuquerque, NM) and was tested for its suitability inbrachytherapy applications in comparison with a similar device by thePhotoelectron Corporation. The depth dose profiles were also compared withthose of two common brachytherapy sources (125I and 192Ir). Thedepth dose characteristics of the radiation were comparable with the twobrachytherapy sources with a slightly reduced attenuation gradient. Thedose rate from the x-ray needle tip was relatively isotropic at the needletip and was continuously adjustable over the range of 0 cGy min-1 toupwards of 62 cGy min-1 at a reference distance of 1 cm in air. Wedetected a significant proportion of x-rays generated along the needleshaft, and not at the needle tip, as intended. The energy spectrum emittedfrom this device had a peak intensity at 21 keV and an average energy of28 keV. The beam was attenuated in both aluminium (the first half-valuelayer being less than 0.1 mm) and in water (50% dose at approximately2 mm). These studies confirm that although there is potential for a systemsimilar to this one for clinical applications, the simplistic electronguidance used in this particular prototype device limits it to researchapplications. Further optimization is required in focusing and steering theelectron beam to the target, improving x-ray production efficiency andusing x-ray target cooling to achieve higher dose rates.