Applying imaging detector data for daily monitoring of dose output in helical tomotherapy

Purpose: In Tomotherapy dose is dependant on the output and shape of the beam (.cone.). Variations in these can have huge influences on IMRTtreatments and daily monitoring is required, but time consuming using conventional methods. Method and Materials: A software package was developed to run independently on the system and retrieve the integrated CT-detector and dose-chamber data. The ability to monitor daily output changes was tested by using static fields and ionization chamber(IC). To validate the link between output, cone and daily patient QA a dedicated IMRT-plan containing disjunctive targets was used and a regression model was built to check the effect variations of cone and output have on this. Results : Results show that the in-house tool can be used to monitor output and cone shape on tomotherapy in a fast and reliable way. Furthermore, the system has the ability of separating effects of output and cone in one single measurement. The static beam measurements using IC show a correspondence within 2% after elimination of the cone effect. Using a 6Dlinear regression the software can predict IMRT-ionization chamber measurements within 0.7%. Early results show that the model.s instabilities model could predict problems such as target failure prematurely. Conclusion : The in-house developed software tool based on direct detector and dose-chamber monitoring can be used to monitor output- and conevariation in 1 procedure. By using a regression the tool can also replace IMRT-QA measurements. Combined, this allows for daily QA-time reduction from 50 to 5 minutes.