Operational Characteristics of a Prototype X-ray Needle Device
Physics in Medicine and Biology
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A prototype x-ray needle, which emits 62.5 kVp x-rays at the tip of a 20 cm long, 4 mm diameter steel needle, has been developed by Titan Pulse Sciences Incorporated (PSI) (Albuquerque, NM) and was tested for its suitability in brachytherapy applications in comparison with a similar device by the Photoelectron Corporation. The depth dose profiles were also compared with those of two common brachytherapy sources (125I and 192Ir). The depth dose characteristics of the radiation were comparable with the two brachytherapy sources with a slightly reduced attenuation gradient. The dose rate from the x-ray needle tip was relatively isotropic at the needle tip and was continuously adjustable over the range of 0 cGy min(-1) to upwards of 62 cGy min(-1) at a reference distance of 1 cm in air. We detected a significant proportion of x-rays generated along the needle shaft, and not at the needle tip, as intended. The energy spectrum emitted from this device had a peak intensity at 21 keV and an average energy of 28 keV. The beam was attenuated in both aluminium (the first half-value layer being less than 0.1 mm) and in water (50% dose at approximately 2 mm). These studies confirm that although there is potential for a system similar to this one for clinical applications, the simplistic electron guidance used in this particular prototype device limits it to research applications. Further optimization is required in focusing and steering the electron beam to the target, improving x-ray production efficiency and using x-ray target cooling to achieve higher dose rates.