This study is a prospective, randomized, open-label, single-center exploratory trial. A total of 40 newly diagnosed, untreated head and neck cancer patients （stage I-IVa, AJCC 8th edition） will be enrolled and randomly assigned in a 1：1 ratio to either the experimental group or the control group. The experimental group will receive radiotherapy immobilization using optical surface guidance technology combined with an open-face mask, while the control group will undergo conventional positioning with a closed head-neck-shoulder thermoplastic mask. The primary objective is to compare the six-dimensional setup errors derived from cone-beam CT （CBCT） registration and intrafraction motion between the two groups. The secondary objective is to compare dosimetric parameters of organs at risk （including lens, eyeball, spinal cord, brainstem, temporal lobe, parotid gland, submandibular gland, thyroid gland, mandible, and temporomandibular joint） between the two groups. The safety of the optical surface-guided open-face mask technique will be evaluated by monitoring radiotherapy-related adverse effects during and after treatment. This study aims to investigate whether optical surface guidance combined with open-face immobilization can improve patient comfort, provide more precise radiotherapy, and enhance the protection of normal tissues.