Book excerpt: RayStation, a new treatment planning system (TPS), was purchased and recently commissioned for clinical use by the institution. As part of the commissioning process, an accurate model of the TrueBeam linear accelerator was made prior to clinical acceptances. Data collection, importing measurements, beam modeling, point dose verifications and clinical plan comparisons are procedures that must be done in order to complete the commissioning of photon and electron energies. During the beam modeling process, various parameters were modified to achieve close matches between the computed and measured PDD curves, as well as measured and computed beam profiles. The tolerance objectives were to have computed data deviating from the measured data within the 2% in fall-off regions, 3% tolerance within in-field and out-of-field regions, and 10% tolerance in build-up regions and penumbra regions [1] . The dosimetric validation procedure followed. Point dose measurements were completed using both the ArcCHECK phantom and the water tank. The majority of the results met the set criteria except for some measurements blocked by MLC leaves or jaws when taken adjacent to the edge of fields. To further confirm the goodness of modeled beams, clinical treatment plans developed with the previously clinically commissioned Pinnacle TPS and imported into the RayStation TPS to generate new plans with same beam arrangements and control points and used as comparisons. After clinical commissioning was completed for RayStation software, a feasibility of using FFF beams to deliver identical or superior beam profile provided by conventional flattened beams of the same energy was investigated. The objective of this research was to show that through sliding window treatment planning, one can create optimized plans and hence no longer the technology of flattening filter is required in modern linear accelerators. To explore this topic, a two stage analysis was carried out. First, delivering doses in a water cube with 10 × 10 to 30 × 30 cm2 open-field 6 MV flattened beams and also create 0.1cm thick square plane structures to be used when undergo the optimization process with 6 FFF beams. Then scaling doses to prescribe 100 cGy at the center of the plane for comparison purpose. The overall uniformity of line profile for FFF beams across the CAX at 10 cm depth showed 1% to 2% superior to flattened beams. For the clinical treatment plans comparison, ten patients were selected with five head and neck cancer plans as well as five lung and mediastinum cancer plans. Original plans were all completed with 6 MV flattened beams and approved by radiation oncologists. New plans were accomplished with 6 FFF beams and same coverages of PTVs were achieved. Most of average mean doses to critical structures and normal tissue volumes receiving 5%, 10%, 20% and 30% of the prescription dose were reduced with FFF plans with slightly increased average max doses.