Room: ePoster Forums
Purpose: The LA45 Racetrack Microtron uses beam scanning techniques to achieve beam flatness and symmetry and its purging magnet can remove contaminant electrons from the beam to improve the surface dose. The high yield of Cerenkov light from its 45MV photon beams holds the promise of a novel treatment modality, radio-dynamic therapy, for late-stage cancer treatment. Although 2D detector array has been routinely used for constancy checks and patient-specific QA in radiotherapy, it has not been reported for 45MV scanning photon beams. Here we present the calibration and characterization of a 2D QA device with our newly installed RaceTrack accelerator.
Methods: In this work, the IBA MatriXX Evolution device was used with a MultiCube phantom. MatriXX contains 1020 vented ionization chambers. To calibrate the Matrixx device, a machine-specific dose calibration factor is needed as well as two other user-defined correction factors: the temperature and pressure correction factor and the additional off-axis calibration matrix. A detailed calibration procedure was developed for this work.
Results: With 100MU delivered to the 2D chamber array, the k_user factor is obtained, 0.726231, from the readings of the 4 central chambers and the input reference dose. The flatness and symmetry of the in- and cross-plane profiles of a 20x20 field measured using the 2D array are consistent with in-water ion chamber measurement, with deviations of 0.78% for flatness and 0.66% for symmetry. With the high â€œshutterâ€? speed of 20ms, the MatriXX system can be used to capture the real-time profile of the scanned beams (scanning cycle~200ms) for any future scanning pattern studies.
Conclusion: This study presents the calibration of the MatriXX system for the LA45 RaceTrack Microtron and demonstrates its applicability for (real-time) beam profile measurement at 45MV photon energy. Further evaluation will be done on the dosimetric performance of MatriXX for treatment plan dose verification.