Protons and ions hold much promise

Charged particle beams (CPB), consisting of protons or carbon ions produced in a cyclotron or synchrotron, are an important development in radiotherapy.1 ^w1 Compared with conventional x rays, charged particle beams produce excellent dose distributions to tumours and reduced doses to normal tissues. They thus hold out the promise of enhanced treatments for cancer and improved quality of life for patients being treated.

All the major technical advances in radiotherapy, such as increasing x ray energies and better target localisation have improved accuracy and outcomes,^{w2 w3} without direct evidence from randomised clinical trials. The one modern exception, conformal radiotherapy (using better shaped x ray beams to conform with tumour geometry), was tested in a randomised trial only in the United Kingdom: the reduction in serious morbidity found has led to extensive use.^w4

Treatment with charged particle beams marks a more radical change from incremental improvements in x ray based therapy. Its safe implementation has been made possible by improved tumour and normal tissue imaging using spiral computed tomography and magnetic resonance imaging, rapid three dimensional dose plan computing, and the industrial manufacture of entire CPB …