Potentiality of proton beam in radiotherapy

The clinical use of protontherapy began in 1954 at Uppsala University in Sweden and in 1961 at Harvard Cyclotron Laboratory (HCL) in Boston, USA. The proton beam has physical and radiobiologic characteristics which differ from those of conventional radiotherapy. The main advantage is due to the Bragg peak that can be modulated and spread out in order to obtain the best coverage of the target volume. The RBE for protons does not substantially differ from that of photons and the value of 1.1 is generally accepted in clinical practice. After a few decades experience, the main clinical indications remain proximity of the target area to critical structures, low tumour radiosensitivity necessitating high doses, and a high benefit to cost ratio. For the tumors that meet these criteria, such as uveal melanomas and chondrosarcomas and chordomas of the base of skull and spinal region, protontherapy may be superior to photon beam therapy. For other malignancies, including tumors of the brain, head and neck, prostate, as well as soft tissue sarcomas, where improved local control is likely to result in higher rates of definitive cure, preliminary results are promisisng but large comparative treatment studies are still needed.