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3 Year Radiation Output Constancy for Xstrahl 300 Orthovoltage Unit

K McCollough*, C Blackwell , Mayo Clinic, Rochester, MN


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Orthovoltage X-ray tubes do not allow users to “tune� beam parameters to achieve a specified dose rate output (cGy/MU or cGy/Min) output. If tube output (Calibration) was to change it would require an edit to the timer set / MU calculation program and verification QA. After 3 years how constant is the output?

Methods: Beam output has been measured weekly with ADCL traceable calibration system, farmer style chamber and electrometer. Various media was used for the measurements These include air, “Solid Water�, and liquid water, with the proper correction factors according to TG-61. In air calibration was by far the most popular using a fixed calibration apparatus.

Results: Four energies were measured weekly for approximately 3 years, (130 different days). The first energy 60 kVp had a range of outputs from 195cGy/Minute 205cGy/Minute with a standard Deviation of 1.95cGy. The second energy 100 kVp had a range of outputs from 213cGy/Minute 231cGy/Minute with a standard Deviation of 2.85cGy. The third energy 180 kVp had a range of outputs from 200cGy/Minute 210cGy/Minute with a standard Deviation of 1.82cGy. The fourth energy 250 kVp had a range of outputs from 186cGy/Minute 193cGy/Minute with a standard Deviation of 1.34cGy

Conclusion: Three of the four energies had less than a 1% standard deviation from the average. The fourth 100 kVp was 1.25% from the average. Over the course of the three years this unit had a X-ray tube replaced at about 9 months, and a ion chamber replaced after another 12 months. New chamber calibration was applied after 2 years due to a change in the ADCL Nx value. With all these changes, multiple calibration media, different chambers, and different people performing the test it was concluded to be very stable output


Quality Assurance, X Rays, Quality Control


TH- External beam- photons: Kilovoltage therapy

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