Development of a preclinical X-rays minibeam Monte Carlo treatment planning system

Minibeam Radiation Therapy (MBRT) delivers spatially fractionated beams, generating alternating high-dose peaks and low-dose valleys, with potential benefits in tumor control and normal tissue sparing. This study presents the development of a Monte Carlo (MC) Treatment Planning System (TPS) for preclinical MBRT, preceded by an investigation of various collimator configurations and a comparison of MC simulations with experimental data. Multiple simulations were conducted to evaluate different combinations of attenuator materials (lead, tungsten) and spacer materials (PMMA, air), as well as various slit widths (0.5-1 mm). Among the tested configurations, tungsten and PMMA emerged as the most suitable materials. As expected, the peak-to-valley dose ratio (PVDR) decreased with depth, while the full-width at half-maximum (FWHM) slightly increased. Fluka and Topas simulations showed good agreement with experimental measurements from gafchromic MDV3 films. A MC-based TPS was implemented to compute dose distributions in mice using CT data and to extract key dosimetric parameters, including PVDR and FWHM. Simulations were performed for a subcutaneous glioblastoma tumor as a case study. Within the tumor volume, the TPS estimated PVDR values ranging from 27 to 16 and a depth-dependent FWHM increase of about 5%. This system provides a robust platform for preclinical MBRT research, supporting treatment planning and delivery optimization.