Parotid cancer is aggressive in growth and the facial nerve is often invaded by the cancer, and the anatomical limitations of the head and neck make surgery not easy to complete. The biological behavior and prognosis of different pathological types of parotid cancer are also different. Based on long-term clinical findings, the low-grade malignant tumor types include highly differentiated mucinous epidermal-like carcinoma, glandular follicular cell carcinoma, epithelial-myoepithelial carcinoma, basal cell adenocarcinoma, and low-grade malignant adenocarcinoma, while moderately low-grade mucinous epidermal-like carcinoma, adenocarcinoma, adenoid cystic carcinoma, salivary gland ductal carcinoma, malignant pleomorphic adenoma, squamous carcinoma, and undifferentiated carcinoma are all highly malignant types. In terms of biological behavior, many parotid cancers, especially those of low to moderate malignancy, are characterized by slow growth, so much so that clinical manifestations alone make them not easily distinguishable from benign tumors, but this slow growth does not diminish their malignant tendency to be more locally aggressive, and in clinical work it is common to see patients with recurrence of parotid cancer years after treatment, even though many of them have received seemingly very successful The treatment method seems to be very successful. Therefore, many factors (biology of local aggressiveness and complex pathological classification, etc.) make parotid cancer a long-standing challenge to treat. Surgical resection is the mainstay of treatment for parotid cancer, especially for a malignant lesion for which surgery is indicated. However, over the years, there are still many debates about the extent of surgical resection and the trade-off of the facial nerve. The facial nerve is anatomically very closely related to the parotid gland, and parotid cancer itself has a neuroinvasive nature, especially if the facial nerve is confirmed to be invaded, the rate of nerve sacrifice will be even higher. Invasion of the facial nerve usually indicates a poor prognosis, and many scholars, when analyzing the prognostic factors of parotid cancer, consider facial nerve invasion as one of the high-risk factors for local recurrence and even distant metastasis. However, for parotid cancer, the results of surgery alone are not ideal, especially for treating those higher stage tumors, even if the facial nerve is sacrificed, it is not easy to obtain satisfactory margins during surgical resection due to the complex anatomy around the parotid gland, so even with more extensive radical surgery, postoperative recurrence is a common phenomenon (27-64%). At the same time, the resection of the facial nerve will lead to permanent facial paralysis, which significantly reduces the quality of survival of patients. Therefore, how to improve the local control rate while preserving facial nerve function has long been a key component of clinical research. Parotid cancer was once considered to be insensitive to radiotherapy, but since the 1970s, surgery combined with postoperative radiotherapy has significantly reduced postoperative recurrence and greatly increased the likelihood of preserving the facial nerve, and the current treatment options for parotid cancer are often based on surgical resection supplemented by postoperative radiotherapy when necessary. Radiation therapy, i.e., the treatment of tumor killing by various kinds of radiation, has a history of more than 100 years and it is one of the important methods of comprehensive treatment for malignant tumors. Classified in terms of treatment modality, radiation therapy includes two basic types: teletherapy and brachytherapy. Compared with external irradiation, the advantages of brachytherapy are mainly reflected in two aspects: the increased dose to the tumor target area and the reduced irradiation volume to normal tissues. In brachytherapy, the irradiated volume is smaller than that of external irradiation, and because the tumor target area is adjacent to the radiation source, most of the energy of the radiation is absorbed by the tissue, thus the irradiation dose to the tumor can be greatly increased. On the other hand, the dose at the edge of the tumor target volume decreases rapidly, so the irradiation amount of normal tissues around the target area is smaller, so that the tolerance of normal tissues is improved, thus significantly reducing the radiation damage to normal tissues. In contrast, when irradiated outside the body, the radiation must pass through the skin and normal tissues to reach the tumor. Especially when the tumor site is relatively deep in, the dose boost to the tumor target area is often greatly limited. In order to obtain a high and uniform dose to the tumor, it is usually necessary to choose a variety of different energy rays and more complicated techniques such as multi-field irradiation.