The overall goal of this research study is to understand how 18F-fluorodeoxyglucose (FDG), a radioactive sugar behaves in head and neck cancer (HNC) and inflammation immediately following injection and at many hours post-injection, with the world's first total-body positron emission tomography (PET)/computed tomography (CT) scanner (EXPLORER).

Inclusion Criteria:

1. Stage II-IVa (American Joint Committee on Cancer, 8th edition) OC who are planned for RT (≥60 Gy) as per routine clinical standard.
2. Patient must be ≥18 years of age.
3. Willing and able to lay motionless in a supine position for up to 60 minutes
4. Patient must be able to provide study specific informed consent prior to study entry.
5. Patient must be able to adhere to the study visit schedule and other protocol requirements (including prolonged fasting).

Exclusion Criteria:

1. Prior RT for any malignancy leading to overlap with planned RT fields.

2. Prior chemotherapy for any malignancy.

3. Subjects suffering from severe claustrophobia.

4. Subjects who have had a research study involving radiation within one year of enrolling in this study

5. Subjects who are pregnant (subjects 18 to 60 years old who are able to become pregnant unless documented hysterectomy or bilateral ovarian removal is available will be tested prior to injection of imaging agent - positive test will exclude from participating in the study)

6. Subjects who are breastfeeding

7. Prisoners.

8. Any significant medical condition that in the opinion of the investigator would prevent the subject from participating and/or adhering to study related procedures or interfere with subject safety (e.g., poorly controlled diabetes).

9. Children (<18 years of age).

10. Body weight more than 240 kg (529 pounds)

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