Room: Exhibit Hall | Forum 4
Purpose: To develop and implement quality assurance procedure of the table motion, the field size and the output utilizing a diode array detector for the novel stereotactic breast radiosurgery device, GammaPod, which has been done with film-based QA. The GammaPod uses multiple Co-60 sources that rotate around the patientâ€™s breast as the table moves to create a highly conformal dose distribution for boosts, partial breast irradiation, or presurgery SRS. This work was done to create a standard quality assurance method for future GammaPod sites.
Methods: Measurements were performed on the SRS Mapcheck in its polymethyl methacrylate breast-mimicking phantom (PMMA). Two separate plans were created to test the field sizes; single isocenter with 25mm field size and single isocenter with 15mm field size. Two additional sets of plans were created to test table motion accuracy. The first set contained 4 separate isocenters with 15mm field size positioned in corners of a 4.2x4.2cm square aligned in the XY & XZ planes. The second sets of plans was identical to the previous set except 3 of the isocenters had an intentional offset of 0.5mm in one of X, Y, and Z direction. These two sets were compared to determine of 0.5mm shift was identifiable.
Results: Field size plans using single shots for 15mm/25mm collimators measured FWHM of 28.9mm and 35.9mm, respectively. Table motion measurements with intentional offsets off 0.5mm were observed to 0.5mm Â± 0.1mm in each direction from the baseline sets. Beam delivery time was identical to the film-based QA, however the analysis time reduced from 1 hr min to 5 min.
Conclusion: We successfully created and implemented the first quality assurance test for SRS that is capable of testing field size and table motion utilizing a diode array device. This procedure replaces film dosimetry for periodic QA, such as the monthly.