Beam's eye view--based radiation therapy: description of methods.

Improving three-dimensional target definitions and dose delivery may improve local control rates in radiation therapy. Computed tomography (CT)-based treatment planning is one step toward achieving this goal, but further progress is possible with beam's eye view (BEV)-based planning. Initially, CT is performed with the patient in the treatment position, and data are transferred to a computerized treatment planning system. Target volumes and vital structures are outlined on CT sections and digitized, and a treatment plan is produced. BEV display is used to calculate the angles needed for oblique fields that would avoid irradiation of vital structures. A BEV printout is obtained along with simulation radiographs. The radiograph is overlaid on the printout, all identified structures are matched, and the target volumes are transferred from the printout to the radiograph. BEV-based planning can improve three-dimensional coverage of a tumor, irradiation techniques, and the therapeutic ratio by decreasing the irradiation of normal tissue. The extra time required for BEV planning is acceptable, but further studies of long-term outcomes and cost-benefit analyses are needed.