A polymer-gel dosemeter, which can be evaluated by nuclear magnetic resonance (NMR), was prepared and then a few samples were homogeneously irradiated by a Leksell gamma knife using an 18 mm collimator (60Co gamma photons) to obtain a calibration curve (NMR 1/T2 response to absorbed dose). To measure dose distribution from the Leksell gamma knife, a testing flask tilled with the gel was fixed in the head phantom and then irradiated based on a calculated treatment plan. Evaluation of dosemeters was performed on a Siemens EXPERT 1T NMR scanner. Dose profiles in X, Y and Z coordinates through the ellipsoidal shape of the dose distribution were obtained to compare experimental results from the irradiated phantom with the treatment planning system calculations. The use of a polymer-gel dosemeter for a verification of stereotactic procedures has some unique advantages which can be summarised as follows: (1) the dosemeter itself is tissue equivalent, (2) three-dimensional dose distributions can be measured, (3) the dosemeter allows patient's procedures to be simulated without any limitations.

Hospital Na Homolce Dept of Stereotactic and Radiation Neurosurgery Prague Czech Republic

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