Radioactive ion beam adaptive treatment of mouse tumors using in-beam PET

During the course of cancer treatment, radiotherapy plans often require adaptation to account for changes in tumor position and patient anatomy. This adaptive approach is especially critical in particle therapy, where organ changes and motion can cause severe dose deviations. In-beam positron emission tomography offers a potential solution for real-time dose verification and treatment adaptation in particle therapy. However, its clinical applicability is currently limited by the low signal-to-noise ratio and the spatial mismatch between activity and dose peaks. These limitations hinder accurate verification of treatment and timely intervention. Here, we demonstrate for the first time that in-beam imaging of radioactive ion beams can enable real-time adaptive treatment of a tumor in a mouse model. We show that dynamic repositioning of a b ⁺ -emitting ¹¹ C-beam along the mouse body results in spatially resolved imaging signals that correlate with distinct treatment outcomes. These findings represent the first evidence of real-time adaptive radiotherapy using radioactive ion beams in a living organism, opening new avenues for precision image-guided particle therapy.