Carbon-ion Radiotherapy for Non-squamous Cell Head and Neck Malignancies

The head and neck region consists of subsites, including the oral cavity, pharynx, larynx, nasal sinuses, salivary glands, and orbits, and contains important organs performing functions that are directly related to the Quality of Life (QOL), such as chewing, swallowing, and phonation. It has been reported that 32% of head and neck cancers occur in the oral cavity, 24% in the larynx, 35% in the pharynx, and 9% in the nasal cavity and sinuses [1]. Histopathologically, more than 95% of head and neck cancers are squamous cell carcinomas. With the advent of an aging society, there has been an increase in the number of people affected by head and neck cancers, including oral and pharyngeal cancers. Since head and neck cancers grow in or invade organs directly related to the QOL, surgical therapy, and, in the case of squamous cell carcinoma, radiotherapy and chemoradiotherapy, play an important therapeutic role. However, non-squamous cell carcinomas, such as adenocarcinoma and adenoid cystic carcinoma, are less radiosensitive to X-rays than their squamous cell carcinomas, and malignant melanoma is radioresistant. Therefore, non-squamous cell carcinomas are less likely to be cured by conventional radiotherapy, making surgical therapy the first-line treatment. However, locally advanced head and neck malignancies are often difficult to treat by surgery in many patients because of anatomical features.