Room: Exhibit Hall | Forum 4
Purpose: To determine the accuracy of beam and dose targeting for the first clinically-implemented ZAP-X system (ZAP Surgical Systems, Inc., San Carlos, CA), a self-shielded stereotactic radiosurgery unit for intracranial treatments.
Methods: Prior to beam-data acquisition, the beam was mechanically steered, and software adjustments were made to each collimator to optimize beam centering and symmetry with the guidance of water tank measurements. Film-based gantry star-shots in the axial/oblique planes were acquired for each collimator and the radiation diameter was quantified. A Winston-Lutz (WL) test was performed for AP/PA and left/right lateral beams by isocentrically targeting a 4mm tungsten BB in an anthropomorphic head phantom with the 10mm collimator. MV images at each beam angle were used to analyze the congruence between the projection of the BB and the radiation field in the three translational directions. An end-to-end (E2E) plan using a single 25mm isocentric shot was generated for a given pre-set beam path (~33-160 beams/path). The 70% isodose line was centered on a Ball Cube (BC) located centrally within a head phantom. The plan (max dose 600cGy) was delivered with Gafchromic EBT3 film placed in axial and sagittal orientations within the BC. Targeting accuracy based on the dose cloud in the three translational directions was determined using a commercial software. Multiple WL and E2E tests were performed to establish isocenter corrections to be applied to the planning CT DRRs for subsequent treatments.
Results: CAX deviation and symmetry at dmax were â‰¤0.28mm and â‰¤0.53%, and the radiation diameter was â‰¤0.67mm for all collimators. Following preliminary WL/E2E tests, isocenter corrections of 0.5mm/0.8mm were applied in the anteroposterior and superior/inferior directions. Average total targeting error in subsequent WL and E2E plans were â‰¤0.48mm and â‰¤0.30mm, respectively.
Conclusion: Beam and dose targeting accuracy is better than 0.5mm in our ZAP-X system.