Clinical complementarities between proton and carbon therapies

Protons are characterised by low LET, but compared with photons and electrons have an improved physical depth dose distribution. Some indications for protons, i.e., ocular melanoma, chordoma and chondrosarcoma of the base of skull or cervical spine, are now accepted by the radiation oncology community as the treatment of choice. Others are still under evaluation, e.g. meningioma, locally advanced nasopharynx tumours, paediatric tumours. Neutrons have the biological advantage of a high LET, but their distribution of dose is in most cases suboptimal. Despite this, there are radiobiological arguments leading to expect that neutrons might be of some benefit in patients with tumours that are resistant to photons, slowly growing or containing a high proportion of hypoxic cells. There is some clinical evidence or rationale for a potential high LET advantage for locally extensive (I think that the current (jargon) word is extended in English..)salivary gland tumours, locally extensive(extended) prostate carcinoma, slowly growing inoperable soft tissue sarcoma, adenocarcinoma, adenoid cystic carcinoma of the paranasal sinuses, melanoma and rectal carcinomas Light ions combine the high LET advantage of neutrons and the improved physical depth dose distribution of protons. The opportunity offered by an optimised distribution of dose should open a new era for high-LET particles, especially in deeply situated x-ray resistant tumours, where the use of neutron beams was restricted by the low quality of their depth-dose profiles. Preliminary results are encouraging.