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A simple approach to using an amorphous silicon EPID to verify IMRT planar dose maps
Author(s) -
Lee Christopher,
Menk Fred,
Cadman Patrick,
Greer Peter B.
Publication year - 2009
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 - 10.1118/1.3075817
Subject(s) - imaging phantom , pinnacle , dosimetry , image guided radiation therapy , ionization chamber , materials science , planar , nuclear medicine , optics , dose profile , radiation treatment planning , medical imaging , calibration , biomedical engineering , physics , computer science , radiation therapy , medicine , radiology , artificial intelligence , computer graphics (images) , ion , quantum mechanics , ionization
A simplified method of verifying intensity modulated radiation therapy (IMRT) fields using a Varian aS500 amorphous silicon electronic portal imaging device (EPID) is demonstrated. Unlike previous approaches, it does not involve time consuming or complicated analytical processing of the data. The central axis pixel response of the EPID, as well as the profile characteristics obtained from images acquired with a 6 MV photon beam, was examined as a function of field size. Ion chamber measurements at various depths in a water phantom were then collected and it was found that at a specific depthd ref, the dose response and profile characteristics closely matched the results of the EPID analysis. The only manipulation required to be performed on the EPID images was the multiplication of a matrix of off axis ratio values to remove the effect of the flood field calibration. Similarly,d refwas found for 18 MV. Planar dose maps atd refin a water phantom for a bar pattern, a strip pattern, and 14 clinical IMRT fields from two patient cases each being from a separate anatomical region, i.e., head and neck as well as the pelvis, for both energies were generated by the Pinnacle planning system (V7.4). EPID images of these fields were acquired and converted to planar dose maps and compared directly with the Pinnacle planar dose maps. Radiographic film dosimetry and a MapCHECK dosimetry device (Sun Nuclear Corporation, Melbourne, FL) were used as an independent verification of the dose distribution. Gamma analysis of the EPID, film, and Pinnacle planar dose maps generated for the clinical IMRT fields showed that approximately 97% of all points passed using a 3% dose/3mm DTA tolerance test. Based on the range of fields studied, the author's results appear to justify using this approach as a method to verify dose distributions calculated on a treatment planning system, including complex intensity modulated fields.