Introduction Microbeam Radiation Therapy (MRT) is a preclinical, spatially fractionated radiotherapy technique that delivers ultra-narrow synchrotron x-ray beams at ultra-high dose rates. MRT has demonstrated superior tumor control compared to synchrotron Broad Beam by triggering infiltration of CD8+ T cells and inducing a transient vascular permeability window. This study aimed to investigate the effects of combining MRT with Gold Nanoparticles (AuNPs) on tumor growth, while also assessing whether MRT could enhance intra-tumoral accumulation of AuNPs.Methods Mice bearing B16-F10 melanoma in their ears were assigned to seven experimental groups, each receiving distinct combinations of priming MRT (150Gy peak-dose), AuNPs, Broad Beam (6.1Gy), and therapeutic MRT (400Gy peak-dose). MRT was delivered as an array of 50µm-wide beams spaced 200µm apart. Tumor growth was monitored daily, while 15nm AuNP uptake was assessed with microCT imaging, electron microscopy, and Image Mass Cytometry.Results Priming MRT increased intra-tumoral AuNP accumulation by 2.5-fold on day 3 and 2.3-fold on day 5 compared to non-primed controls. Image Mass Cytometry showed that AuNPs distributed across the tumor stroma and concentrated at the tumor periphery, near areas with high vascular density and in M2-like macrophages. Combining priming MRT with AuNPs and therapeutic MRT achieved the best tumor growth delay and regression with a median survival to 39.5 days; significantly longer than the 17 days achieved with priming MRT, AuNPs, and broad beam. The sensitizer enhancement ratio of 1.38 highlighted the efficacy of AuNP-enhanced MRT.Conclusion Our study introduces a novel approach in cancer therapy, demonstrating that MRT serves as both a potent standalone treatment and an effective enhancer of drug delivery. MRT increased the tumoral concentration of AuNPs and could potentially do the same with other therapeutic agents. Our findings strongly advocate for the continued development of MRT-based combination regimens and highlight the clinical potential of this dual-mechanism approach.
