Monte Carlo study of high-energy light ions for minibeam radiation therapy approach

Minibeam Radiation Therapy (MBRT) is an innovative development in radiation therapy, offering enhanced normal tissue-sparing compared to conventional approach. Light ions possess favorable physical and radiobiological properties over X-ray and heavy-charged particle beams. New facilities like the Facility for Antiproton and Ion Research (FAIR) and Marburg Ion-Beam Therapy Center (MIT) enable the delivery of high-energy ion beams. This study examined the potential for further improvement in MBRT utilizing high-energy light ions through Monte Carlo simulations performed with GEANT4. We investigated the irradiation patterns of broad, single minibeam, and minibeam arrays of proton and light ions (Z ≤ 3) beams in a water phantom, varying minibeam widths and center-to-center (ctc) distances. The study analyzed the contribution of secondary particles, peak and valley doses, and peak-to-valley dose ratio (PVDR). Our findings demonstrate that minibeams of heavier ions (compared to protons) show higher PVDRs for the same energy and configuration. The enhanced immune activation capacity of these ions may compensate for the larger PVDRs’ potential impact on tumor control. High-energy ions minimize the effects of multiple Coulomb scattering (MCS), enhancing the PVDR in healthy tissues. This reduction improves their directional precision as they move through tissues, resulting in sharper dose distributions. Additionally, a larger ctc (3.5 mm) further improves normal tissue preservation. However, higher PVDRs at greater depths may compromise tumor control, underscoring the need for strategies like cross-firing or using multiple minibeam arrays to achieve homogeneous dose distributions. Results suggest that high-energy proton MBRT can significantly benefit during treatment. While the primary advantage of light ions, such as helium-4, might lie in their potential for theranostic applications. However, they offer superior dosimetric advantages compared to heavier ions due to the reduced contribution of fragment products. Biological validation and advanced accelerator facilities are essential for experimental verification of these findings.