Premium
SU‐E‐T‐232: Using EPID Images for MLC QA: A Northwestern Memorial Hospital Experience
Author(s) -
Pokhrel D,
Gopalakrishnan M,
Luo G,
David J,
Sathiaseelan V
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612182
Subject(s) - linear particle accelerator , image guided radiation therapy , collimator , nuclear medicine , medical imaging , dicom , position (finance) , digital radiography , computer science , optics , radiography , artificial intelligence , physics , medicine , beam (structure) , radiology , finance , economics
Purpose: To verify experimentally MLC leaf gaps position using EPID images for an advanced radiotherapy treatment delivery such as IMRT, SBRT. Methods and materials: EPID images were acquired with 6 MV x‐rays of Elekta linear accelerators utilizing garden fence image technique, with 8 and 11‐strips of MLC preset values at 0o, 90o, 180o, and 270o gantry angles. The dark strips were created by eleven exposures of 0.5×20.0cm2 strip fields, which were separated by 20mm gaps. The eight exposures were of 2.0×20.0cm2 strip fields separated by 5mm gaps. These images were exported for analysis in dicom format. The EPID images were filtered to reduce background distortion and enhanced MLC leaf edge. In‐house software was used to estimate inter‐MLC leakage and absolute MLC leaf gaps position. The accuracy of EPID‐based MLC leaf gaps position detection was estimated by comparing with the known preset‐MLC leaf gaps. Results: In all measurements, the inter‐MLC leakage was less than 1.5%. Using simple strip‐test patterns, the MLC leaf gaps position determined from EPID images agreed to within ±0.5mm of the corresponding preset values. Difference images show significant effect of gravity in MLC leaf motion along lateral gantry angles. Summary and Discussion: Our preliminary results show EPID images can be used as an alternative to radiographic films for routine‐QA of MLCs. Since, the EPID is rigidly‐mounted with linear‐accelerator and digital‐intrinsically, it could be more accurate and convenient MLC QA tool than that of the conventional film. In addition, the EPID images can be acquired easily, analyzed automatically, and stored more rapidly and conveniently than that of radiographic films. Availability of EPID on all new linear‐accelerators makes it a promising tool for quantitative MLC QA. Routine clinical application of EPID‐based MLC QA will be helpful for more accurate delivery of highly modulated IMRT and SBRT plans, including VMAT.