The potential of the innovative proton minibeam radiation therapy (pMBRT) could be verified in the past by preclinical experiments. It was shown that side effects in mouse ears can be completely avoided for beam spot sizes below 0.1 mm. Such beam spot sizes with sufficiently high beam intensity have so far only been prepared at the Maier-Leibnitz-Laboratory (MLL) in Garching. However, the maximum proton energy that can be achieved by the tandem Van de Graaff accelerator used there limits the penetration depth of the protons to a few millimeters.

In order to demonstrate the full potential of pMBRT for deeper tissue (e.g. muscle, lung, or even tumors), a concept for a preclinical irradiation facility is being developed at the LRT2 institute, aiming at a proton penetration depth of approx. 40 mm into tissue.

Irradiation facilities consist of a multitude of complex components which interact with the particle beam. Therefore, the conceptual design goes hand in hand with simulations by which the interaction of all components is evaluated and optimized.

Here, the focus at our institute is primarily on the simulation and development of the beam transport system and the components required for the preclinical application. 

The beam transport system consists of ion optical elements like quadrupole and dipole magnets. It has the task to direct the proton beam to the target, where a beam spot of less than 0.1 mm is formed. The arrangement of the ion optical elements is optimized by beam dynamics simulations, using programs such as TRACE 3-D. The resulting particle distributions are then calculated using particle tracking programs such as TRAVEL, COMSOL or CST Studio Suite.

For preclinical application, a scanning unit for moving the proton beam over the target, an exit window for extracting the proton beam from the beamline, and a dosimetry unit for determining the applied dose are being developed. Since the dosimetry unit and exit window are directly traversed by the proton beam, they have a great influence on the beam quality. The interaction of the protons with relevant elements of the components required for the application is therefore simulated and evaluated in advance with GEANT4 or TOPAS to determine the resulting beam spot size.