Upgrading an Integrating Carbon Ion Transmission Imaging System with Active Scanning Beam Delivery towards Low Dose Ion Imaging

The dosimetric advantages of ion therapy come at the cost of an increased sensitivity to range inaccuracies in the treatment planning and delivery stages. This prompts the development of imaging techniques capable of an accurate assessment of the relative stopping power (RSP). We investigate carbon-ion imaging based on a prototype integration-mode detector working as a range telescope. Experiments were conducted at the Heidelberg Ion-Beam Therapy Center with active pencil beam scanning. The aim of this article is to experimentally operate the imaging system in low-dose regimes. Therefore, an adjustment of the synchronization mechanism between beam delivery and data acquisition was required. Different from the previous studies, this article investigates unexplored dosimetric scenarios and faced the related technological challenges. Radiographic and tomographic images of two tissue-equivalent phantoms were acquired and the image quality was evaluated. Relying on dedicated signal processing to solve the range mixing problem, the tomographic images showed an RSP accuracy of better than 0.6%. This article evaluates the imaging performance with low-dose exposure, focusing on the technological requirements and pointing out the current limitations. Hence, this article supports the development of upgraded integration-mode ion imaging systems for reducing range uncertainties in particle therapy.