Two carbon ion facilities were built and shut down in Germany.
Here's an old article on the story:
A prototype for proton and ion therapy has been used clinically in Heidelberg since 2009. Built jointly by Siemens and GSI (Helmholtz Centre for Heavy Ion Research) in Darmstadt.
healthcare-in-europe.com
Kiel was dismantled completely by Siemens. Marburg was taken over by Heidelberg and now running after several issues were encountered.
It was quite a shame. The main problem was the expectation of how many patients could be treated with carbon ions vs. the reality of how little we understand carbon ions.
Surely you can treat peripheral NSCLC (SBRT-like), liver tumors, localized prostate cancer, chordomas, chondrosarcomas, but the main problem with carbon ions is the unknown radiobiology behind them. Trying to treat fast repopulating tumors (for example head&neck cancer) with carbon ions may actually be counterproductive. You may be dealing more damage to healthy tissues than tumor itself.