Half of the approximately 4 million annual cancer cases in Europe receive radiotherapy. While many cancer patients have benefitted from technical improvements in recent years, widespread diseases, such as pancreatic and lung cancer, still have dismally low cure rates, with median survival of less than 2 years. Carbon ion radiotherapy (CIRT) offers unprecedented precision in delivering tumour dose, and can be the much needed game changer for these patients. However, CIRT is vulnerable to uncertainties in patient positioning, anatomy changes and organ motion. The current clinical approach is to increase the high dose volume to ensure target coverage, counteracting the primary advantage of CIRT. Novel strategies for image guidance and beam range assessment are crucial to unlock the full potential of CIRT for the best possible patient care.
 PROMISE, for the first time, will produce mixed ion beams that enable concurrent treatment and image guidance. Carbon ions deliver the dose to the target while Helium ions, simultaneously accelerated to the same velocity, traverse the patient and monitor tumour location and beam range. PROMISE realizes true portal imaging, providing real-time information on the target anatomy as seen by the treatment beam. Coupled with innovative detectors, AI-based image recognition, and online dose reconstruction, this technique will enable to drastically reduce safety margins, and achieve the full potential of CIRT.
 The GSI accelerators are uniquely suited to develop the first mixed beam of Carbon and Helium, along with strategies for their cost-effective translation to existing and future clinical CIRT centres. The method is validated experimentally in GSI’s former CIRT treatment room. Patient simulation studies will highlight clinical benefit and characterize ideal use cases. A demonstration in an animal model will pave the way for clinical transition. The mixed beam image guidance of PROMISE will lead to a paradigm shift in CIRT.

Funded by the European Union (ERC, PROMISE, 101124273). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them.