Improvement of kilovoltage beam output with a transmission x-ray target: Radiological optimization and cooling system design

The purpose of this work is to introduce the design of a transmission x-ray target suitable to be used in kilovoltage x-ray tubes such as those employed in orthovoltage x-ray therapy. The target consists of a 20 μm thick tungsten slab deposited on top of a 1 mm copper plate. Monte Carlo simulation is used to determine both the energy absorbed in the tungsten and copper slabs, and also to calculate the characteristics of the resultant x-ray production. The absorbed energy distribution in the target is then fed into a finite element software to determine the heat distribution and its evolution in time as a function of both the electron current incident on the target and the focal spot size. A cooling system is proposed and modeled based on these results to prevent the target assembly from melting. Absorbed dose rates in water are also calculated for both the proposed transmission and a standard reflection target as a function of the incident electron current. We show that, compared to the reflection target, our design increases by more than 100% the emission of x-rays, and that the proposed cooling system is capable of operating at a sustained power rating above 4 kW.