SU‐E‐T‐201: Dosimetric Comparison of Patient Specific IMRT QA Using Varian DynaLog Files and TPS Calculations in a Phantom Geometry

Abstract

Purpose: To evaluate significance of gamma index between the planned 2D doses by Eclipse treatment planning system and the calculated 2D doses based on DMLC Dynalog information for patient specific IMRT QA. Methods: DMLC (Dynamic Multi‐Leaf Collimator) of IMRT (Intensity Modulated Radio Therapy) delivery information recorded in log files during delivery. The Dynalog file includes amongst other, the beam on and off status, segment dose index, and individual leaf positions. In this study, previous treated IMRT patient plans are selected and delivered using a Varian CLINAC 600 C/D linear accelerator equipped with Millennium 120 MLC. IMRT verification plans were generated on PTW OCTAVIUS phantom using Eclipse TPS. Dynalog file data were recorded during delivery and were converted to fluence maps using an in‐house Matlab code. The fluence maps were imported to Elipse TPS and dose distributions on the OCTAVIUS phantom. PTW VeriSoft was used to compare the planned and recalculated IMRT plans. Gamma index, profiles and isodose distributions were used to evaluate the dosimetric difference. Results: The comparison of the planned and the recalculated dose distribution showed that the gamma index passing rate was 90% or greater for all plans using a 3%/3mm criteria. The analysis of the results based on the complete 3D dose distributions is under investigation. Conclusion: Our preliminary results show that the dynalog files can be an alternative method for patient specific IMRT QA. Good agreement between measurements and calculations was achieved in all cases tested and further investigation for calculations using patient geometry and for VMAT is in progress.