Collimated and non-collimated proton minibeam irradiation using SIRMIO: a simulation study

Successful clinical integration of pMBRT requires comprehensive investigations of the relationship between various pMBRT parameters and their associated biological effects. Such investigations are critically dependent on small animal models. Therefore, a state-of-the-art small animal irradiation platform like SIRMIO (Small Animal Proton Irradiator for Research in Molecular Image-guided Radiation-Oncology), capable of delivering precisely controlled spatially fractionated doses, is highly desirable for advancing preclinical pMBRT research.

This in silico study evaluates the SIRMIO beamline's capability to deliver beams essential for pMBRT experiments. We used Geant4-based Monte Carlo simulations to investigate two configurations: one without a collimator, and one using a 30 mm thick brass multislit collimator (MSC). For both configurations, we examined center-to-center (CTC) of 3, 4, and 5 mm, with a constant 1 mm slit width when MSC is used.

The SIRMIO beamline can effectively generate spatially fractionated dose profiles with varying CTC. Without a collimator, sufficient dose contrast for pMBRT can be achieved with CTC of 4 mm and above, as evidenced by peak-to-valley dose ratios (PVDR) of 3.44 and 6.57 for 4 and 5 mm CTC, respectively. MSC further enhances dose contrast, achieving PVDR of 11.3, 20.7, and 28.7 for 3, 4, and 5 mm CTC, respectively. Furthermore, we explored interlacing beams as a means of achieving a uniform target dose while preserving dose contrast in normal tissue, demonstrating the potential of this approach using the SIRMIO beamline.

The SIRMIO platform can be a viable option for pMBRT experiments.