Application of polymer gel dosimetry in gamma knife radiosurgery.

Object: The purpose of this study was to investigate the use of a polymer gel-based dosimeter for the evaluation of geometric and dosimetric inaccuracies during gamma knife radiosurgery and during the irradiation of an experimental animal.

Methods: A polymer gel dosimeter, based on acrylic monomers, was used for experiments conducted in this study. The accuracy of the dosimeter was evaluated on a Siemens EXPERT 1-tesla scanner in the transmitter/receiver head coil with the use of a multiecho sequence with 16 echoes, TE 22.5 to 360 msec, TR 2000 msec, slice thickness 2 mm, field of view 255 mm, and a pixel size of 0.5 x 0.5 mm2. Two experiments were conducted. First, the head phantom containing the polymer gel dosimeter was irradiated using 4-, 8-, 14-, and 18-mm isocenters. Second, a specially designed rat phantom was irradiated by four 4-mm isocenters. The dose profiles in the x, y, and z axes were calculated in the treatment planning system and measured with the polymer gel dosimeter and the results were compared. There was good agreement between the measured and calculated dose profiles. The maximum deviation in the spatial position of the center of measured and calculated dose profiles was 0.5 mm in the head phantom and 1 mm in the rat phantom. The maximum deviation in the width of the selected reference isodose of measured profiles was 1.2 mm in the head phantom and 1.1 mm in the rat phantom.

Conclusions: The use of the polymer gel-based dosimeter for the verification of stereotactic procedures has advantages compared with other dosimetric systems. The dosimeter itself is tissue equivalent. Three-dimensional dose distributions can be measured and the dosimeter allows simulation of the therapeutic procedures.