Clinical microbeam radiation therapy with a compact source: specifications of the line-focus X-ray tube

Abstract

Background and purpose: Microbeam radiotherapy (MRT) is a preclinical concept in radiation oncology with arrays of alternating micrometer-wide high-dose peaks and low-dose valleys. Experiments demonstrated a superior normal tissue sparing at similar tumor control rates with MRT compared to conventional radiotherapy. Possible clinical applications are currently limited to large third-generation synchrotrons. Here, we investigated the line-focus X-ray tube as an alternative microbeam source. Materials and methods: We developed a concept for a high-voltage supply and an electron source. In Monte Carlo simulations, we assessed the influence of X-ray spectrum, focal spot size, electron incidence angle, and photon emission angle on the microbeam dose distribution. We further assessed the dose distribution of microbeam arc therapy and suggested to interpret this complex dose distribution by equivalent uniform dose. Results: An adapted modular multi-level converter can supply high-voltage powers in the megawatt range for a few seconds. The electron source with a thermionic cathode and a quadrupole can generate an eccentric, highpower electron beam of several 100 keV energy. Highest dose rates and peak-to-valley dose ratios (PVDRs) were achieved for an electron beam impinging perpendicular onto the target surface and a focal spot smaller than the microbeam cross-section. The line-focus X-ray tube simulations demonstrated PVDRs above 20. Conclusion: The line-focus X-ray tube is a suitable compact source for clinical MRT. We demonstrated its technical feasibility based on state-of-the-art high-voltage and electron-beam technology. Microbeam arc therapy is an effective concept to increase the target-to-entrance dose ratio of orthovoltage microbeams.

A Multi-Scale and Multi-Technique Approach for the Characterization of the Effects of Spatially Fractionated X-ray Radiation Therapies in a Preclinical Model

“…Over the past years, technical efforts have been also addressed for the development of alternative X-ray sources for MRT and MB for translation into clinical practice. As an example, line-focus X-ray tubes are being considered as microbeam source and Monte Carlo simulations have demonstrated they have a great potential as a radiation source for clinical application [ 82 ], of MRT. With this respect it is also important to mention recent studies in which in-vitro MRT treatments performed with laboratory sources at conventional dose rates enhanced an increased tumor cell sensitivity [ 83 , 84 ].…”

Heat management of a compact x‐ray source for microbeam radiotherapy and FLASH treatments

“…A thermionic cathode and anode produce a 300 keV electron beam, which propagates along the beamline. Focusing magnets around the beamline shape the electron beam into a strongly eccentric focal spot (details in Winter et al 12 …”

“…Additional to the homogeneous, rectangular electron distribution, we investigated an electron distribution based on the phase space resulting from previous simulations of the electron accelerator for the LFxT. 12 Here, the electron beam had full widths at half maximum of 50𝜇m × 20mm. The energy deposit per voxel was converted into heat power density using Matlab (version 2018b, The MathWorks, Inc., Massachusetts, USA) and normalized to a primary electron current of 0.3 A.…”

Divide and conquer: spatially fractionated radiation therapy

“…61) and line-focus X-ray tube (Ref. 62), may allow for the first systematic and comprehensive radiobiology experiments and facilitate the translation of the technique to clinical trials.…”