Study of 2D ion chamber array for angular response and QA of dynamic MLC and pretreatment IMRT plans

Abstract

Aim

To study of 2 Dimensional ion chamber array for angular response and its utility for quality assurance of dynamic multileaf collimator and pretreatment intensity modulated radiotherapy plans.

Materials and Methods

The MLC QA test patterns and IMRT plans were executed on 2D ion chamber array having 1020 vented pixel ionization chambers. The dynamic MLC QA test patterns were chair test, x–wedge, pyramid, open swipe field, garden fence and picket fence. Performance of Dynamic wedges was compared with physical wedges. For IMRT verification, five patients with localized prostate carcinoma were planned using dynamic IMRT technique. Angular response of MatriXX was measured by exposing the system from different gantry angles.

Results

Dynamic MLC QA tests such as chair, x-wedge, pyramid, and open swipe field were successfully verified. MatriXX was not able to recognize the bar pattern of picket test and garden fence test. The response of MatriXX gradually decreases from 0° to 180° angles and it was 7.7% less at 180° angle. The dynamic wedge profiles were matching with corresponding physical wedge profiles. For pretreatment IMRT QA, the average dose difference between planned and measured dose was 1.26% with standard deviation of 1.06.

Conclusion

I'mRT MatriXX can be used for routine dynamic MLC and IMRT pretreatment QA but care should be taken while taking measurements in penumbra region because of its limited spatial resolution.