Treatment-plan evaluation using the dose quality factor (DQF) for dynamic conformal arc (DCA)-based radiosurgery on patients presenting with an intracranial tumor

The aim of the present study was to find the optimum dynamic conformal arc (DCA)-based radiosurgery conditions for treatment of patients with intracranial tumors. DCA plans were generated on a commercial treatment-planning system (BrainSCAN v.5.31) for various beam-number and gantry-angle combinations by using computed tomography (CT) scans to delineate the planning target volume (PTV) and the organs at risk (OARs). To evaluate planning quality related to the various planning conditions, we analyzed the dose quality factors (DQFs) for 22 patients as a function of the number and the total angle of arcs related to the target volume, which were determined on the basis of patient-specific features. When the total angle of arcs was less than 250°, the DQF values were under 0.98 (worst group). When the total angle of arcs was more than 350 degrees, the DQF values were maximized, and the highest DQF values (best group, DQF > 0.995) occurred in the range between 50 and 120°/cm 3 for the total angle/target volume condition. In this optimal range of angle/volume, the asymmetric distribution of the arcs resulted in decreased DQF values. For a relatively large target volume (more than 10 cm 3 ), the DQF values were lower than these for a relatively small target volume (less than 10 cm 3 ). Re-planning results showed that the planning quality could be improved using optimized planning conditions. We expect that this study will provide a basis for the evaluation of various DCA conditions prior to actual planning and treatment.