A. Background Information The long-term objective of this proposal is to advance the treatment of cancer using laser plasma accelerator physics breakthroughs at LBNL to build a miniature electron accelerator as a variable Xrays source with clinically relevant dose-rates of ~0.7 Gy/min and energies between 0.25 – 5 MeV. This electronic particle brachytherapy source is powered by a commercial, laser system, operating up to 1000 Hz and 7 W of average power. The flexibility of the laser driver allows treatment with radioisotope-free operation and variable x-ray energy on a pulse-by-pulse basis. This confers extra degrees of freedom for the treatment planning process thus providing the clinician the ability to improve the dose delivery. Unwanted dose to nearby healthy tissue and critical structures is reduced. This proposal brings a world-class team together: LBNL in laser plasma accelerators and optical fiber-based delivery systems, Woodtoga to translate the technology into clinically relevant products with expertise in bonding and the creation of miniature X-ray devices, and Varian Medical Systems as the commercial partner. Integrating the technology with clinical practice, treatment planning, into a radiation oncology platform transforming the field of brachytherapy.