The purpose of the study is to see how practical it is to inject a radiotracer called 99m-Technetium Sulfur Colloid around the tumors for the imaging of patients with oropharyngeal cancer.

This study will evaluate a technique called lymphatic drainage mapping. This is a technique where a radiotracer (a radioactive material that can be seen with a special computed tomography [CT] scanner to create 3D images) is injected into a vein around the tumour, either with local anesthesia or under general anesthesia. The radiotracer that will be used for the lymphatic drainage mapping is called 99m-Technetium Sulfur Colloid. Images will be taken of neck to detect the movement of the radiotracer. This will allow the doctors to see the drainage pattern of the lymph nodes in the neck.

The information from this study will be used to better understand the tendency for oropharyngeal cancers to spread to lymph nodes. In addition, the information from this clinical trial will be used in future clinical studies to help specialists identify strategies to help plan treatment based on this type of imaging study.

Inclusion Criteria:

• Patient has lateralized oropharyngeal carcinoma (tonsil or tongue base) not involving midline
• Has squamous cell carcinoma, T1-3 tumours, with no contralateral nodes on clinical exam or axial imaging
• Human papillomavirus (HPV) positive or negative
• Patient should have normal organ function as per Investigator judgement
• Patient is planned for definitive or adjuvant radiotherapy (RT) or chemo radiotherapy (CRT) with bilateral neck RT, or surgery
• Eastern Cooperative Oncology Group (ECOG) performance status 0-1

Exclusion Criteria:

• T4 tumours
• Contralateral/bilateral nodal disease or node(s) > 6cm on clinical exam or axial imaging or positron emission tomography (PET)
• Primary tumour involving or crossing midline
• Soft palate or posterior pharyngeal wall tumour subsites
• Previous head and neck cancer
• Previous radiotherapy (RT) to the head and neck
• Previous neck dissection
• Distant metastases
• Prior invasive malignancy (except non-melanoma skin cancer) unless disease free for 3 years
• Prior radiotracer allergy
• Multiple primary head and neck cancers
• Pregnancy