Exhibit Hall | Forum 4
Purpose: To describe new methods used for geometric and dosimetric verification of the GammaPod ™system
Methods: The GammaPod™ system (Xcision Medical Systems LLC, Columbia, MD) acceptance tests were performed according to the manufacturer guidelines. Commissioning tests included verifications of static and dynamic geometric accuracy, point dose and isodose distribution, treatment interruption and completion, and dose repeatability. Twelve test plans, with different target sizes and location, were created from the GammaPod Treatment Planning System (TPS) Release 1.2 (Xcision Medical Systems LLC) and delivered to a water phantom with an Exradin A1SL ion chamber (Standard Imaging Inc) and an SRS MapCHECK (Sun Nuclear Cooperation) in both axial and sagittal position. The IAEA-TRS No.483 was followed for the dose calculation of the ionization chamber measurements. Novel commissioning tests included tracking table motion accuracy with a Polaris camera (NDI-Northern Digital) and measurement of absolute dose in the medium density assumed by the TPS (0.935g/cm3). To directly compare the absolute dose calculation from the TPS, coconut oil of density 0.93g/cm3 was used for the measurements.
Results: The base acceptance and commissioning results were all within specification. The point dose difference of the A1SL ion chamber in a water phantom measurement to the TPS was 1.6±0.9% [Range: -2.1-2.8%]. The isodose distribution showed an average gamma of 3%/2mm passing rate of 98.3±2.5% and 99.8±0.3% for axial and sagittal, respectively. The dose repeatability was within 0.4% and the treatment interruption was verified to be within 0.5%. The accuracy of the table motion was confirmed to within 1mm and the absorbed dose in medium was confirmed within 3.4%.
Conclusion: The GammaPod system performs as expected both mechanically and dosimetrically . The use of coconut oil with near identical physical density as used in the TPS and the use of 3D optical tracking confirmed the accuracy of the system.
Not Applicable / None Entered.