Oral cavity cancers generally occur in 40-60 year old males, and are associated with the habits of cigarette smoking, drinking alcohol, and chewing betel quid. In addition, chronic inflammation, poor nutrition, poor oral hygiene, or inadequate dental aids are possible reasons. Combination therapy is needed to increase tumor control, including surgery, radiotherapy, and chemotherapy. The disease control rate, or long term survival rate, is dependent on the tumor stage. According to our previous data for resected cases, the 5-year overall survival rates for stage I-II, III, and IV were 80~90%, 70~80%, and 40~60%, respectively. However, it will widely vary based on different tumor locations or with certain risk factors.

High energy X-ray is generally used for radiotherapy to treat deep tumors. With different techniques for treatment planning and dose delivery, such as 3-dimensional conformal radiotherapy, intensity-modulated radiotherapy (IMRT), Tomotherapy, volume-modulated radiotherapy (VMAT), or RapidArc radiotherapy, better tumor coverage dosing with less normal tissue dosing can be achieved by these advanced techniques. However, there is still a substantial unpreventable dose scattering that surrounds normal tissue through X-ray. As a consequence, the treatment-related xerostomia, dysphagia, neck fibrosis, and radiation-related dental caries are the problems in treating head and neck patients. In contrast, proton beam treatment has a Bragg peak, which means a large amount of energy is released at the desired depth, but the entrance dose is low and no dose exists after the desired depth. With the development of intensity-modulated proton therapy (IMPT), proton beams can effectively cover the treatment field, while sparing the surrounding normal tissue from dosage. Decreasing the integral scattering dose can be translated into clinical benefit.

Reviewing recent literature, the clinical application of proton beam therapy in oral cavity cancer is sparse, but experiencing rapid development, due to its complexity of treatment. The main method of treatment is surgery with or without flap reconstruction. Therefore, postoperative tissue swelling, body changes, metal plate/screw implantation, and reproducibility of head-neck positioning should be taken into clinical considerations. Since the pass length of a proton beam is highly sensitive to tissue depth, density of material, or tissue inhomogeneity. Adequate image processing, robust planning, and image-guided radiotherapy (IGRT) are required for dose correction and precise dose delivery. In addition, bilateral neck prophylactic irradiation is generally required for oral cavity cancers. To cover complex targets, proton pencil beam spot scanning with an intensity-modulated technique is developed to effectively cover the treatment field, but spare the surrounding normal tissue from dosing. IMPT leads to better treatment tolerance and a long-term quality of life. However, in many clinical situations, whether to choose proton beam therapy or not will depend on disease status, surgical procedure, and patient status. Well discuss with the doctors to choose the most optimal treatment technique is needed. It is important to discuss with your doctor which is the most optimal treatment technique for your case.

Article author: Dr. Chien-Yu Lin

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