The optimal management of head and neck squamous cell carcinoma typically involves primary surgical resection, and the indications for adjuvant radiotherapy are based on pathologic markers of intermittent - and high-risk disease, which include positive margins, extracapsular nodal extension, lymphovascular invasion, and perineural invasion (1-3). Trismus is one of long term sequelae of radiotherapy for head and neck cancer patient. The prevalence of trismus after head and neck oncology treatment could be as high as 42% (4). It is significantly reducing nutrition due to impaired mastication (5). The loss of function appears to be related to damage and fibrosis to the muscles of mastication. Radiation therapy involving the temporomandibular joint, the pterygoid muscles, the temporalis or the masseter muscle is most likely to result in trismus (5, 6). Moreover, there may be scar tissue from radiation or surgery, nerve damage, or a combination of these factors (6, 7). In addition, the doses of RT levels in excess of 60 Gy (8) or the configuration of the radiation field increasing (9) are more likely to cause trismus. These data were documenting the clinical results of conventional radiotherapy (RT).