Room: AAPM ePoster Library
Purpose: AAPM TG-142 recommends monthly beam output checks for varying dose rate, gating, dynamic wedges, and electron energy. Ion chamber arrays are capable of performing dosimetric measurement with the proper corrections implemented. This work evaluates the accuracy of using an ion chamber array, in combination with energy wedges and a web-based QA platform, for monthly beam constancy QA in comparison to an ion chamber in water technique.
Methods: The Sun Nuclear IC PROFILER with Quad Wedges (ICP) was used in conjunction with SNC Routine, a web-based QA system, to measure monthly beam quality and output across six Varian Truebeams over the course of fifteen months. All machines were equipped with four photon energies and four machines were also equipped with five electron energies. Measurements using a Farmer-type ionization chamber in water (FCW) were taken in conjunction and manually recorded in SNC Routine. Measurement results and session times for both techniques were extracted via SQL query from the SNC Routine database.
Results: ICP reduced overall measurement time compared to FCW for photons and electrons by 50% and 66%, respectively. Both systems showed similar bias and variation in output measurement, 0.3% ± 0.7% and 0.4% ± 0.7% for ICP and FCW, respectively. Energy and session matched output differences between systems were normally distributed with a bias of 0.1% ± 0.6% and IQR of 0.4% across all energies as both techniques exhibited similar dispersion. R50 and D10 beam quality measurements were more consistent using ICP than FCW with RMSE values of 0.05 and 0.19 mm for electrons and 0.14 and 0.53% for photons, respectively.
Conclusion: The combination of IC PROFILER with proper baselines and the SNC Routine system provides similar output measurement, more consistent beam quality, and improved efficiency in comparison to a Farmer chamber in water technique.
Funding Support, Disclosures, and Conflict of Interest: Travel support from SNC to present at SNC QADS2020.