Premium
A novel approach to accurate portal dosimetry using CCD‐camera based EPIDs
Author(s) -
Franken E. M.,
de Boer J. C. J.,
Heijmen B. J. M.
Publication year - 2006
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 - 10.1118/1.2172746
Subject(s) - dosimetry , imaging phantom , optics , physics , deconvolution , medical imaging , photon , computer science , nuclear medicine , artificial intelligence , medicine
A new method for portal dosimetry using CCD camera‐based electronic portal imaging devices (CEPIDs) is demonstrated. Unlike previous approaches, it is not based on a priori assumptions concerning CEPID cross‐talk characteristics. In this method, the nonsymmetrical and position‐dependent cross‐talk is determined by directly imaging a set of cross‐talk kernels generated by small fields (“pencil beams”) exploiting the high signal‐to‐noise ratio of a cooled CCD camera. Signal calibration is achieved by imaging two reference fields. Next, portal dose images (PDIs) can be derived from electronic portal dose images (EPIs), in a fast forward‐calculating iterative deconvolution. To test the accuracy of these EPI‐based PDIs, a comparison is made to PDIs obtained by scanning diode measurements. The method proved accurate to within 0.2 ± 0.7 % (1 SD), for on‐axis symmetrical and asymmetrical fields with different field widths and homogeneous phantom thicknesses, off‐axis Alderson thorax fields and a strongly modulated IMRT field. Hence, the proposed method allows for fast, accurate portal dosimetry. In addition, it is demonstrated that the CEPID cross‐talk signal is not only induced by optical photon reflection and scatter within the CEPID structure, but also by high‐energy back‐scattered radiation from CEPID elements (mirror and housing) towards the fluorescent screen.