The compact line-focus X-ray tube for microbeam radiation therapy - Focal spot characterisation and collimator design.

Purpose: Microbeam radiation therapy (MRT) has shown superior healthy tissue sparing at equal tumour control probabilities compared to conventional radiation therapy in many preclinical studies. The limitation to preclinical research arises from a lack of suitable radiation sources for clinical application of MRT due to high demands on beam quality. To overcome these limitations, we developed and built the first prototype of a line-focus X-ray tube (LFXT). During commissioning, characterisation of the X-ray focal spot is necessary. For the generation of microbeams, we require a specially designed collimator adapted to the LFXT.

Methods: We present an adapted edge method and a pinhole method for focal spot measurements of the LFXT prototype as well as the design of the microbeam collimator with a slit width of 50μm, spaced by 400μm. Monte Carlo simulations validated the focal spot measurement techniques and the design of the collimator.

Results: We showed that the adapted edge method is more complex but superior to the adapted pinhole method in terms of quantitative validity. Simulations for the microbeam collimator showed a sharp microbeam dose profile with a peak-to-valley dose ratio (PVDR) above 23 throughout 50 mm of water.

Conclusion: During commissioning, the adapted focal spot visualisation methods will be used to determine the focal spot dimensions and to optimise machine parameters. The LFXT prototype will enable preclinical MRT with significantly higher dose rates than any other compact MRT source and will pave the way for the first clinical trials in a hospital setting.