Room: AAPM ePoster Library
Traditional Tomotherapy IMRT verification work has some manually errors which would bringa system error in machine output dose, a much more precision IMRT verification method should be created to replace the traditional way.
We found the output dose-error differenceresultswere not coincide betweenstatic and Dynamic inDaily output dose check. Finally, weworked out the reason was that the IMRT verification work we have done in treatment planning system (TPS) commissioning was not very precise.We re-did the TPS IMRT verification work by using the on-site cheese phantom CT image and IVDT to create new TomoPhan IMRT plans and tested these plans dose again. We analyzed the Static and Dynamic output dose results after modified the machine output.
Before we modified the machine output dose, we analyzed 85 days static and Dynamic output dose results, and the Average and Standard deviation dose-error difference for staticoutput was 0.09%±0.267, the same values for Dynamic output was 1.835%±0.33. We got 73 daily check results for static and Dynamic output dose after we redid the IMRT verification work and modified the machine output dose, the mean and standard deviation of dose-error difference results for static output were -0.307% ±0.509 and those values for Dynamic out were 0.223% ±0.78.
Conclusion: system error was brought in because the cheese phantom CT image and IVDT used in IMRT verification work are not those belong to the on-site cheese phantom. The difference of factory cheese phantom and on-site cheese phantom may have indefinite density difference. And this difference may result on a wrong IMRT output modification. So, use the on-site cheese phantom and its own image and IVDT to do the IMRT varication work in Machine TPS commissioning is necessary.