Trail Evaluating Carbon Ion Radiotherapy (3 GyE Per Fraction) for Locally Recurrent Nasopharyngeal Carcinoma

The purpose of this study is to determine the maximal tolerated dose (MTD) of re-irradiation using carbon ion radiotherapy (CIRT) with the fraction size of 3 gray equivalent (GyE) in the treatment of locally recurrent nasopharyngeal cancer (NPC) and to evaluate the efficacy of such treatment at the MTD. Participants will be treated with CIRT with escalating dose regimens to evaluate the MTD in terms of acute and subacute toxicity observed within 4 months after the completion of CIRT. Once the MTD for locally recurrent NPC is determined, the MTD will be used as the recommended dose to patients fulfilling the inclusion criteria in the Phase II part of the trial.