Room: AAPM ePoster Library
Purpose: To commission and validate the dosimetric accuracy of the SDX spirometer gating system for use in deep inspiration breath-hold (DIBH) for proton pencil beam treatments.
Methods: The SDX system provides a gating trigger signal to the IBA Proteus Plus. Two static phantoms were used to evaluate absolute dosimetry accuracy: one consisted of a calibrated parallel plate ion chamber, and another of a cross-calibrated 2D ion chamber array, both in solid water. To evaluate motion artifacts, an end-to-end test employed an in-house motion phantom based on the Quasar Modus phantom and the Accuray Ball-Cube-2 phantom, which accepts a pair of custom-cut EBT3 films in the axial and sagittal planes. The static tests used SOBP and select patient fields that were long enough to be interrupted up to three times. The motion phantom plans were created based on a CT scan of the phantom to fit a spherical target with a 3 mm margin using two and three field arrangements. The motion phantom was aligned using the fiducial markers embedded in the phantom using kV images. Two sets of measurements were made, one without motion and another in DIBH with one interruption per field. 2D gamma analysis compared uninterrupted against interrupted measurements from 2D array on a 1%/1mm criteria, while films were compared against planned 3D dose on a 3%/3mm criteria. Film measurements were normalized to plan values.
Results: The ion chamber measurements were within 0.2% in all scenarios. The gamma analysis of the 2D array yielded 100%. The film comparison against planned dose yielded gammas above 95% in all scenarios for both 2 and 3 fields plan.
Conclusion: The presented commissioning process ensured accurate and reproducible results of the SDX spirometer system.