Purpose: Increased normal tissue tolerance to proton minibeam radiotherapy (pMBT) has been demonstrated in numerous preclinical studies. However, inter-institutional reproducibility of experimental results at different facilities with different beam energies is lacking. The aim of this work was to develop a transportable preclinical pMRT system that can be reproducibly set up at different proton facilities.
Methods: A physical collimator arrangement was developed to produce high dose peak and low dose valley regions. Monte Carlo simulations were carried out in TOPAS to optimize key parameters of the set-up like field size and peak to valley dose ratio (PVDR). The system was tested at the University Proton Therapy in Dresden using a 150 MeV beam and at the University of Washington in Seattle using a 50 MeV preclinical proton beam. Both beams were characterized by means of film dosimetry and micro-diamond measurements.
Results: The system consists of a pre-collimator and a pMRT slit collimator, spaced 1 m apart. Attached to the pre-collimator is a PMMA plate, to widen the beam to homogeneously illuminate the minibeam collimator with its divergent slits. Optimal alignment between the two is achieved with rotational stages. Set up and fine adjustment was achieved within several hours. The resulting pMRT field covers 10x10 mm² and has 250 µm wide beamlets with a center to center spacing of 1 mm. Film dosimetry revealed PVDRs of 8 in Dresden and 17 in Seattle. Film dosimetry and micro-diamond measurements agreed within 10% relative error.
Conclusion: The novel transportable pMRT system has been developed and was successfully set up and verified at two different institutions. The set-up is versatile and can be used independently of the proton source enabling comparative preclinical in vivo and in vitro research and paves the way for further studies in understanding the mechanisms of spatially fractionated proton therapy.
Not Applicable / None Entered.