Although the core function of the accelerator complex is the use in particle therapy, as mentioned, the dual function linear accelerator will also allow parallel production of radioisotopes for nuclear medicine. The usage of a linear accelerator would allow more efficient production with deuteron and alpha particle beams compared to cyclotrons due to increased beam transmission [38, 39]. Production of radioisotopes would be completely independent from the ion therapy and scientific research functions, as it would be done with additional beam pulses in the linear accelerator structure only. Operation mode for the synchrotron is foreseen at 1 Hz, while for the linear accelerator – at 50 Hz. As the linear accelerator can be modulated on pulse-to-pulse basis, the beam can be independently adapted for the different functions of the facility [38, 39].

While various radioactive isotopes for production have been considered from the technical possibility perspective, survey data from clinical users were presented within the framework of the PRISMAP Consortium [40,41,42]. With a total of 114 respondents from 30 European countries and 104 different institutions (out of which 48 respondents from research institutions and 40 clinical institutions) the main interests and demands for the future in nuclear medicine are for theragnostic and targeted alpha therapy isotopes – actinium-225 and other alphas emitters, copper-64 and isotopes from scandium and terbium families. Possible use of such isotopes would also be a novelty for the Baltic States, as currently only more conventional isotopes are used such as fluorine-18, technetium-99m, iodine-123 and iodine-131, lutetium-177, radium-223.

Integrating these clinical interests into the technical design of the facility is highly important. As production of non-conventional isotopes could be done in the proposed facility, possible export pathways should be considered in co-operation with the 2 soon-operational cyclotron production facilities in Lithuania and Latvia [43][44].

Development of a particle therapy centre within the Baltic States based on NIMMS helium synchrotron technology is a unique opportunity for the region to evolve both in clinical and scientific research capacity. From the technological point of view, the accelerator complex provides customizability to user needs, vast research spectrum possibilities, while keeping R&D risk minimal owing to standard technology usage in the design. The customizability also corresponds to the envisioned usage of such a facility – both as a scientific research centre and a clinical treatment facility. One of the key considerations before further developments was, of course, whether the number of patients eligible for particle therapy would be sufficient to run such a facility. The first estimates presented here have shown a promising starting point, which prompts for more in-depth analysis of this aspect in the future.

An important aspect regarding the availability of cancer statistics data for such an initiative was also put forward. For long-term goals of this initiative, development strategies are needed to provide state-of-the-art national cancer registries. Improvements can be considered for the existing registries in Lithuania and Estonia, though this aspect is even more important in Latvia, as currently a dedicated registry is lacking, which already complicated some of the data collection procedures. A consensus within the workshop was reached that the creation and improvement of national cancer registries are crucial for the success of such a proposed facility, as this data is necessary to make joint decisions between the 3 Baltic States on the number of eligible patients, as well as patient referral and reimbursement system functioning. From a clinical perspective, strengthening the support of the Baltic medical community for this initiative is crucial. A long-term project of this scale cannot be planned without clear and direct support from the medical communities of the region.

Throughout the workshop, the importance of scientific research function was discussed heavily, as well. As the helium synchrotron would be a custom-made particle accelerator, the scientific research function of the proposed facility is of high importance, with a broad programme to be foreseen. Pre-clinical and clinical research will be of high importance to develop the role of helium ion therapy in cancer treatment. The facility would also provide research opportunities in medical physics, dosimetry, accelerator physics, and related technology development, while the use of the linear accelerator for radioisotope production – in nuclear medicine, nuclear physics, radiochemistry, material science, and others. The proposed facility has a large scientific research potential, thus a more detailed programme is to be developed in the future within the foreseen feasibility study, as discussed next.

Findings of the workshop have gathered support both from medical communities and political bodies within the Baltic States for further investigations of the feasibility of such a facility. Such investigations are planned to be carried out in a dedicated longer-term feasibility study done by Baltic States specialists and researchers in close collaboration with CERN experts. The length of the feasibility study is envisioned to be 2 years, with the finalization of the programme and working plan currently on-going. The feasibility study is to focus on 3 main areas: cancer epidemiology in the Baltic States and clinical aspects, technical integration of the helium synchrotron into a dedicated facility and lastly – economic aspects.