MLC leaf position and dynalog file accuracy QA procedure using the EPID

ABSTRACT

A main concern about the IMRT dose validation tool using Monte Carlo [MC] simulation and R and V-system/Dynalog file is the potential inconsistency between the actual leaf-end positions and those recorded by the Dynalog file. The present study investigates a method to validate the accuracy of the Dynalog tiles using amorphous silicon electronic portal imaging device [aSi-EPID] images. A computer program was developed to detect the MLC segmented field edges in EPID images [l024x768 pixels, pixel size 0.392 mm], Standard reference MLC segmented fields were designed and leaf-end positions were measured accurately. EPID images for these reference MLC fields were recorded and the leaf-end positions were calculated as the locations where the image intensity is 50% of the maximum. Small corrections were made to minimize the effect of scattered photons [background]. Daily EPII] images of the same MLC segmented fields were compared to the original images and to check the accuracy of the Dynalog files. A daily QA tool was developed to check the accuracy of the Dynalog file and MLC leaf end positions as part of the comprehensive IMRT-QA procedure. This ensures the accuracy of the MC based patient-specific IMRT dose verification using the information recorded in the Reeord and Verify system/Dynalog files