Protons to replace photons in external beam radiation therapy?

Protons provide the basis for superior distribution of radiation dose due to the physical characteristics of protons. Proton beams used in radiation therapy can be designed to yield a uniform dose across the target and then virtually zero deep to the target and lower dose proximal to the target (for non-superficial lesions). Such beams can be employed in comparable number, direction, weighting, angulation, intensity modulation as is feasible for photon beams. The result is a smaller treatment volume, and hence a lower incidence and frequency of treatment-related morbidity. Importantly, the reduction in treatment volume permits a higher dose to the tumour. This means an improved tumour control probability and lower normal tissue complication probability. Clinical gains appear to have been realized in the treatment of patient with uveal melanoma, skull-base sarcoma, para-nasal sinus carcinomas, selected stages of lung carcinoma and hepatocellular carcinoma. There are now three proton therapy centres with gantry systems with seven more being built. Further, there are seven additional centres in active planning. At present, prospective clinical evaluations are in progress for tumours at many anatomical sites.