Salivary Flow Quantification: For unstimulated resting sialometry, each patient will be instructed to first clear the mouth by swallowing. With the head held slightly forward, the patient will be instructed not to swallow during the 5-minute collection, but to allow saliva to collect in the floor of mouth. The patient will expectorate the accumulated saliva into a pre-weighed 100 mL vial after 60 seconds. The patient will repeat this procedure 4 more times for a total collection time of 5 minutes. At the end of the 5 minutes, the collection vial will be promptly sealed and weighed. For each collection, the actual clock time at the start and end of the collection will be recorded as well as the vial weight before and after the collection of the sample. Stimulated sialometry will then be performed. Patients will rest for 5 minutes prior to collection. The exogenous stimulant will be 20 mL of citric acid solution held in the mouth for 1 minute. After the patient expectorates this solution, 5-minute saliva collection will take place as described above. These measurements will be done by the radiation oncology research nurse.