Room: ePoster Forums
Purpose: Orthovoltage X-ray tubes do not allow users to â€œtuneâ€? 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, â€œSolid Waterâ€?, 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