Premium
Sci—Sat AM(2): Brachy — 08: Evaluation of an A‐Si EPID in Direct Detection Configuration for Transit Dosimetry in Radiotherapy
Author(s) -
Sabet M,
Vial P,
Menk FW,
Denham JW,
Greer PB
Publication year - 2010
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 - 10.1118/1.3476220
Subject(s) - dosimetry , dosimeter , image guided radiation therapy , imaging phantom , ionization chamber , nuclear medicine , materials science , detector , medical imaging , optics , medicine , physics , ionization , radiology , ion , quantum mechanics
The accuracy of dosimetry measurements using a‐Si EPIDs is affected by their structural characteristics particularly due to the presence of the Gd 2 O 2 S phosphor layer. Our previous measurements have shown that modification of the structure to direct detection configuration by removal of the phosphor layer can improve the imager properties for transit dosimetry applications. In this study a research dedicated Varian a‐Si EPID has been changed to direct detection configuration and evaluated for transit dosimetry measurements using 7 prostate and 9 IMRT fields with a 20 cm thick phantom in the beam by comparison to a MatriXX detector array. The EPID images were converted to dose using a calibrated 0.6 cc ionization chamber. Gamma evaluation (3%, 3 mm criteria) of the results for for all points greater than 10% of the maximum dose showed that the fraction of points with a Gamma index less than 1 was at least 94.6% in head and neck fields and 99.3% in prostate fields. The mean Gamma was 0.360 and 0.288 for head and neck and prostate fields, respectively. In conclusion, The EPID results are very close to the reference dosimeter and the direct EPID appears to be a promising device for online patient dosimetry applications for the future.