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A Rapid and Comprehensive Procedure for Daily Proton QA

T Zhao

T Zhao*, B Sun , K Grantham , N Knutson , L Santanam , S Goddu , E Klein , Washington University, St. Louis, MO


SU-E-T-432 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The objective is to develop a rapid and comprehensive daily QA procedure implemented at the S. Lee Kling Proton Therapy Center at Barnes-Jewish Hospital.

Methods: A scribed phantom with imbedded fiducials is used for checking lasers accuracy followed by couch isocentricity and for X-ray imaging congruence with isocenter. A Daily QA3 device (Sun Nuclear, FL) was used to check output, range and profiles. Five chambers in the central region possess various build-ups. After converting the thickness of the inherent build-ups into water equivalent thickness (WET) for proton, range of any beam can be checked with additional build-up on the Daily QA3 device. In our procedure, 3 beams from 3 bands (large, small and deep) with nominal range of 20 cm are checked daily. 17cm plastic water with WET of 16.92cm are used as additional build-up so that four chambers sit on the SOBP plateau at various depths and one sit on the distal fall off. Reading from the five chambers are fitted to an error function that has been parameterized to match the SOBP with the same nominal range. Shifting of the error function to maximize the correlation between measurements and the error function is deemed as the range shift from the nominal value.

Results: We have found couch isocentricity maintained over 180 degrees. Imaging system exhibits accuracy in regard to imaging and mechanical isocenters. Ranges are within 1mm accuracy from measurements in water tank, and sensitive to change of sub-millimeter. Data acquired since the start of operation show outputs, profiles and range stay within 1% or 1mm from baselines. The whole procedure takes about 40 minutes.

Conclusion: Taking advantage of the design of Daily QA3 device turns the device originally designed for photon and electron into a comprehensive and rapid tool for proton daily QA.

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