Role of FDG in the management of radiation-induced complications in patients with head and neck malignancies

Objectives: Explain the association between FDG uptake and glucose metabolism in areas of inflammation in patients with head and neck malignancies. Demonstrate the importance of FDG in evaluating the local and systemic effects of head and neck radiation therapy. Assess the benefits of proton radiation therapy over photon radiation therapy in head and neck cancer patients.

Methods: 18-fluorodeoxyglucose (FDG) has been established as an effective tracer to use in hybrid positron emission tomography/computed tomography (PET/CT), as its uptake into tissues is proportional to glucose metabolism, which makes it an indicator of structures that rapidly consume glucose for energy. As a result, FDG-PET/CT has revolutionized the staging, management, and follow-up of patients with head and neck (HN) tumors. Beyond cancer, FDG-PET/CT can be utilized to identify areas of inflammation in the body. Because it has been demonstrated that radiation therapy (RT) can cause inflammation in off-target anatomical structures, such as the parotid gland, FDG-PET/CT is particularly useful for patients receiving RT who experience systemic effects that impede recovery. For example, photon RT has been shown to introduce vascular complications, which can be life-threatening. This review will assess the power of FDG-PET/CT in assessing areas of FDG uptake before and after RT, which can aid in recognizing weaknesses in current therapies and improve the treatment of RT-induced complications. Discussion: In contrast to MRI or CT alone, FDG-PET/CT can monitor metabolic changes and precise anatomic locations of these fluctuations in HN cancer patients, even before large structural changes have occurred. Not only can FDG-PET/CT accurately identify HN tumors, but it can also recognize other parts of the body that have been affected by RT. For example, preliminary results in our lab have utilized FDG-PET/CT to identify increased parotid gland glucose metabolism following RT in HN cancer patients, indicative of parotitis and xerostomia. Similarly, we demonstrated increased intravascular FDG uptake in the carotids and aorta following photon RT, suggesting a correlation between photon RT and vasculitis. To reduce these off-target effects, proton instead of photon RT may be a powerful alternative treatment modality. In contrast to photon RT, proton RT delivers less off-target radiation to surrounding healthy tissues, resulting in fewer complications. We predict the utility of FDG-PET/CT in identifying areas of increased metabolic activity in the body, both in the identification of HN tumors and in the recognition of widespread inflammatory effects which may result as a consequence of RT. Future studies will utilize FDG-PET/CT to demonstrate the superiority of proton RT as a treatment for HN malignancies.

Conclusions: The purpose of this educational item is to establish the power of FDG-PET/CT as a reliable method to identify and track metabolic changes in glucose uptake in HN cancer patients. This technique can be used to monitor systemic inflammatory changes as a result of RT and related to chemotherapy, which can be of use in the management of off-target complications, such as in the parotid gland or in nearby vascular structures. Future prospective studies should be conducted using FDG-PET/CT to compare patient outcomes with proton and photon RT, as well as to identify areas of the body that may be prone to inflammatory side effects.