Portal images are acquired for patient positioning and tumor localization prior to or during radiation therapy using a linear accelerator (linac). A treatment planning system (TPS) is used to simulate treatments of a specific patient and calculate the dose delivered to that patient. Some linear accelerators are equipped with a lower nominal energy that is commonly used for portal imaging. The lower nominal energy allows for higher quality images to be produced. This work aims to commission a 2.5 megavoltage (MV) imaging beam on the TrueBeam linac using the Eclipse TPS.