Clinical Indications for Carbon Ion Radiotherapy.

Compared with photon and proton therapy, carbon ion radiotherapy (CIRT) offers potentially superior dose distributions, which may permit dose escalation with the potential for improved sparing of adjacent normal tissues. CIRT has increased biological effectiveness leading to increased tumour killing compared with other radiation modalities. Here we review these biophysical properties and provide a comprehensive evaluation of the current clinical evidence available for different tumour types treated with CIRT. We suggest that patient selection for CIRT should move away from the traditional viewpoint, which confines use to deep-seated hypoxic tumours that are adjacent to radiosensitive structures. A more integrated translational approach is required for the future as densely ionising C-ions elicit a distinct signal response pathway compared with sparsely ionising X-rays. This makes CIRT a biologically distinct treatment compared with conventional radiotherapy.