Dose distribution measurements by means of gel-layer dosimeters. Evaluation of algorithms for artifacts amendment

One of the major necessities that appears with the continuum development of conformal radiotherapies is a corresponding improvement of dosimetric techniques. Fricke gel-layer dosimetry, coupled with a suitably developed software, has proven to be a reliable technique for 3D absorbed dose distribution verification. The method is based on the measurement of optical transmittance of the gel-layers. The experimental assessment consists basically in a planar illumination source and a computer-controlled CCD camera for the acquisition of optical transmission images. Two possible sources of errors might alter the right dose distribution evaluation, namely defects in the gel structures and problems related to the non-uniform illumination source. Various algorithms for the detection and amendment of both kinds of artifacts were evaluated on a series of properly chosen gel-layers images. Dose profiles along the central axis of a phantom irradiated with different X-ray therapy fields and evaluated with the proposed algorithms were then compared with ionization chamber measurements. The obtained results indicate a good reliability of the proposed method.