Proton/heavy Ion Therapy in Salvage of Locally Recurrent Nasopharyngeal Carcinoma

Radiotherapy is the major modality for treating advanced local recurrence of nasopharyngeal carcinoma (NPC). However, as the nearby critical neurological structures have already absorbed a dose close to their maximum tolerance in the primary treatment, even state-of-the-art intensity modulated radiotherapy (IMRT) cannot achieve a satisfactory dose distribution, and re-irradiation is often associated with serious, or even fatal, late complication, as well as substantial local failure. Proton/heavy-ion therapy, with their superior energy deposition characteristics and biological effectiveness, have the potential to overcome these obstacles. The use of proton/heavy-ion therapy to treat re-current NPC dates back to the last millennium when such facilities were extremely rare and dose delivery technique was in its infancy (mainly passivescattered beams from very limited directions were available). Over the last two decades there have been substantial technological development in proton/heavy-ion therapy, the facilities have become much more widely available, with proton therapy being accepted as a suitable mean for re-irradiation setting in general. The advancement in diagnostic technology and systemic treatment have also contributed significantly to the effectiveness of such highly conformal radiotherapy modalities. Many have applied proton/heavy-ion therapy in the extremely challenging recurrent NPC situation, with various degrees of success. This article provides a brief review of the basic principle of proton/heavy-ion therapy, the issues unique to their usage, studies on their application in treating recurrent NPC and their possible future development.