Enhancing pre-clinical microbeam radiation therapy capabilities at PETRA III beamline P61A through high-precision beam delivery

Microbeam radiation therapy (MRT) exploits spatially fractionated, micrometer-scale X-ray beam arrays that deliver high-dose (peak) and low-dose (valley) regions. At beamline P61A of the PETRA III synchrotron (DESY, Hamburg, Germany), MRT delivery has been limited to a fixed 2 mm wide field and single-direction irradiation. This study aimed to implement stereotactic multi-port MRT (STX-MRT) with lateral field extension and to quantify the spatial reproducibility of the microbeam arrays during patched and multi-angle delivery. Approach: A custom motorized stage providing vertical and lateral translation and rotation was developed to enable discrete lateral patching and sequential delivery from multiple ports (1-9). Each microbeam array comprised five peaks with a beam width of 50 µm and a centre-to-centre spacing of 400 µm. Spatial accuracy was assessed with Gafchromic™ HD-V2 film scanned at 7.9 µm resolution. Fifteen films (three per geometry), corresponding to 225 patched arrays, were included to determine the spatial accuracy. Main results: Beam delivery was highly reproducible. In 88% of the microbeam arrays, deviations were below the detection limit (≤7.9 µm). Detectable displacements occurred in 12% of arrays and ranged from 33 to 258 µm, typically localized to individual patches or ports. The rotational isocentre remained stable across all configurations, and increasing the number of ports and delivery speed did not introduce systematic alignment errors. Significance: Reliable lateral field patching and multi-port MRT delivery with micrometre-scale precision was achieved, extending the usable irradiation field and enabling stereotactic MRT at beamline P61A. This technical capability broadens the range of irradiation of different target sizes and supports advanced preclinical studies of MRT.