Garchinger Maier-Leibnitz-Kolloquium: "Siebstrahlung” – An Old Idea with New Beams: Spatially Fractionated Radiotherapy with Proton Minibeams

by Prof. Niels Bassler (Aarhus University and Danish Center for Particle Therapy (DCPT), Aarhus, Denmark)

Thursday 30 Oct 2025, 16:15 → 17:15 Europe/Berlin

Lecture Hall, ground floor (west) (LMU building, Am Coulombwall 1, campus Garching)

More than a century ago, early radiotherapists discovered that filtering X-rays through metal grids, called “Siebstrahlung”, could reduce skin damage. The idea was later abandoned when high-energy beams made such filtering unnecessary. In recent years, several groups have revived the principle in new forms of spatially fractionated radiotherapy, most notably as GRID and Minibeam Radiotherapy (MBRT). In Proton Minibeam Radiotherapy (pMBRT), narrow proton beamlets spaced a few millimetres apart produce sharply modulated dose patterns that have shown remarkable normal-tissue sparing in preclinical studies.
Quantifying this effect remains challenging because conventional dose metrics are not meaningful in heterogeneous fields. To make fair comparisons, we introduced an outcome-based framework that defines the therapeutic window directly through experimentally measurable endpoints such as tumor control and normal-tissue complication probabilities. At the Danish Centre for Particle Therapy (DCPT), we have built dedicated MBRT collimators for our clinical proton system and performed in-vivo studies. We observed a striking reduction in acute normal-tissue toxicity while maintaining tumor control. No measurable severe damage occurred even at doses that would cause complete injury under conventional proton therapy. In quantitative terms, tissues tolerated almost twice the tumor dose that produced severe injury in conventional therapy, yet still showed no measurable normal-tissue toxicity. The magnitude of this effect suggests that spatial fractionation with protons may represent one of the most pronounced examples of normal-tissue protection observed in radiobiological research so far.
Building on these findings, DCPT is now developing adaptive collimator systems that can vary the beam spacing dynamically, for example by using a moiré-based dual-collimator design. Supported by the newly formed PRESTO consortium within the EU PIANOFORTE program, this next phase will focus on systematically quantifying the spatially fractionated radiotherapy effect using protons. The work will explore optimal collimator configurations and develop radiobiological modeling based on the experimental studies, with the overall aim of translating pMBRT into clinical practice.

Hybrid access via ZOOM:
https://lmu-munich.zoom.us/j/98457332925?pwd=TWc3V1JkSHpyOTBPQVlMelhuNnZ1dz09
Meeting ID: 984 5733 2925
Passcode: 979953

 

 

kolloquium-30-10-25.pdf