• To use computed tomography (CT) scans to measure and guide your radiation therapy. [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  

• To learn if the CT scans can be used to adapt radiation therapy to the changes in normal tissue and to the shrinking of the tumor that may occur as a reaction to radiation therapy [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  
• To see if magnetic resonance imaging (MRI) scanning can detect certain changes in the tumor any earlier than with standard tests. [ Time Frame: 2 years ] [ Designated as safety issue: No ]
  

Inclusion Criteria:

1. Patients older than 18 years of age with histologically proven squamous cell carcinoma of the oropharynx, dispositioned to receive definitive radiotherapy for intact primary tumor.
2. Stage III, IVa, or IVb disease as defined by American Joint Committee on Cancer (AJCC) cancer staging criteria.
3. ECOG performance status 0-2.

Exclusion:

1. Patients who have undergone definitive resection of the primary tumor.
2. Prior cancer diagnosis, except appropriately treated localized epithelial skin cancer or cervical cancer.
3. Prior radiation therapy to the head and neck region.
4. Patients unable or unwilling to give written, informed consent or to undergo MRI imaging.
5. Women of childbearing potential (A woman of child-bearing potential is a sexually mature woman who has not undergone a hysterectomy or who has not been naturally postmenopausal for at least 24 consecutive months [i.e., who has had menses at any time in the preceding 24 consecutive months]) and male participants must practice effective contraception (oral, injectable, or implantable hormonal contraceptive; tubal ligation; intra-uterine device; barrier contraceptive with spermicide; or vasectomized partner) throughout the study
6. Patients unable to tolerate DW-MRI or DCE-MRI.
7. Patients who have had prior chemotherapy.