Missing Link Found:Trending Flatness On Both Axes in SNC Daily QA 3
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PO-GePV-T-322 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Sun Nuclear’s Daily QA offers an efficient solution to daily QA needs. Checking monthly profile flatness consistency is a recommendation of TG 142. Daily QA however, reports a single flatness value which combines transverse and radial profiles. To measure each profile separately, the user should be able to efficiently calculate it using saved raw data. Unfortunately, the raw data contained in Daily QA's datafile is missing correction factors that would help to efficiently reproduce the same readings as on the day of measurement. These correction factors account for variations in the intrinsic ion chamber sensitivity and/or output on the day of device calibration. We provide a neat solution to obtaining these correction factors so that flatness can be trended efficiently along each axis.
Methods: Beam data is automatically saved within a datafile without correction. The corrected readings are also accessible by selecting each trend point. However, doing so is time-consuming. We take the ratio of one corrected reading to that in Daily QA’s datafile to obtain correction factors per ion chamber location. The readings on 5 ion chambers are of interest to us—2 located transversely, 2 radially and 1 on the central axis. This array of energy-specific correction factors can be applied to all subsequent raw readings in the datafile.
Results: We compared flatness obtained using the method described to that obtained on the day of measurement. The average difference was 0 (standard deviation within ± 0.05). Using this method, we have shown that a day-to-day trending of flatness on both radial and transverse axes is still possible even if the original dose correction factor is unavailable.
Conclusion: The missing link has been found allowing users to efficiently trend flatness over time on each axis using Daily QA 3. Our method also meets monthly QA recommendations for flatness.
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