Poster — Thur Eve — 32: Water tank referenced calibration method for detector array devices

Introduction:Detector array devices, such as the I'mRT Matrixx (IBA Dosimetry), provide a means of evaluating beam profiles with respect to gantry for a range of dose rates and monitor units. The relative calibration of these devices is typically highly susceptible to even relatively small variations in beam output. An alternative method is proposed here, which directly references the device detector response to water tank data. Methods: The Matrixx response was measured at the four cardinal angles for three devices. A calibration factor was determined for each orientation of the Matrixx device by dividing a water tank measured profile by the Matrixx response for the in‐plane and cross‐plane detectors. A geometric mean of each orientation was used as the estimate of the calibration coefficient. Results: Before calibration, the three‐detector average of the deviation from the profile measured in the water tank centered on each of the horns was 0.4% (SD 0.2%); applying the calibration procedure reduced this to 0.1% (SD 0.1%). The energy independence of the proposed relative calibration was also confirmed. A comparison of the linac output for relatively short Matrixx acquisitions to the longer water tank acquisition suggested some difference. This difference was mitigated by averaging. Conclusions: The proposed water tank reference calibration procedure is an effective means of determining the relative calibration of a detector array and mitigates the effect of compound error by avoiding the recursive algorithm of typical calibration methods. In addition it has the benefit of being directly relatable to commissioning beam data.