Transportation dose and doses to extracranial sites during stereotactic radiosurgery with the Leksell Gamma knife.

Two dosimetric aspects of Leksell Gamma knife (LGK) treatment have been investigated in this study: (a) measurement of the small dose (transportation dose) which is absorbed during the patient's transportation into and out of the treatment position within the ionization chamber, and (b) measurements of the doses absorbed by the eyes, thyroid, breast, abdomen, gonads, knee and ankle during the treatment using thermoluminescent dosimetry (TLD). The transportation dose was 0.253 +/- 0.003 Gy, which represented 8.4% of the dose rate (3.005 Gy/min) during measurements. In vivo TLD measurements have been performed on 51 patients. The doses measured in organs and sites of interest were 0.223 +/- 0.168 Gy for the eyes, 0.081 +/- 0.050 Gy for the thyroid, 0.049 +/- 0.033 Gy for the breast, 0.024 +/- 0.18 Gy for the abdomen, 0.012 +/- 0.008 Gy for the gonads, 0.003 +/- 0.002 Gy for the knee and 0.002 +/- 0.002 Gy for the ankle. During LGK radiosurgery, doses to extracranial sites and organs depend mainly on the total target dose and the number of shots used for the treatment. These doses are generally low; the maximum dose was measured for the eyes (approximately 0.7% of the maximum target dose), and the doses to other body organs decrease with increasing distance from the isocenter of the LGK radiation unit.