Thermal modelling of a kilovoltage X-ray source for portal imaging

The authors have developed a finite element model that exactly matches the dimensions of the megavoltage target assembly of a Varian 2100C/D linear accelerator. The geometry of the model has then been modified to include a kilovoltage target with a 300 target angle. Using this modified model, along with accurate knowledge of the heat transfer mechanisms in the target assembly (e.g., forced convection heat transfer, fully developed boiling, and critical heat flux), the authors have predicted the thermal behaviour of the model. The results show that for a 1.0 mm thick tungsten target more than 2000 W can be applied when using a small area heat source and more than 3000 W can be applied when using a large area heat source. The authors´ studies suggest - from a thermal perspective - that it should be possible to incorporate a kilovoltage X-ray source inside the head of a medical linear accelerator