Computational model for the estimation of the extracranial doses received during Leksell gamma knife model C treatment.

Abstract

Extracranial doses received by patients undergoing Leksell gamma knife surgery (GKS) can be of clinical concern. Therefore, the ability to preestimate peripheral doses received outside the treatment field during the GKS would be beneficial and could be used for the optimization of treatment planning by providing a reference for practitioners to calculate the extracranial dose burden to the body before the start of treatment. A dose of 40 Gy was delivered to the Rando phantom in a single fraction to a midline hypothetical target close to the center of the skull. Treatment planning was performed for multiple isocenters with a prescription to the 50% isodose of each collimator. Treatment plans were produced for 1, 5, 10, 15, and 20 shots, keeping the same dose and dose distribution at different target volumes. An automatic positioning system was used for positioning the phantom during the treatment. The doses to different organs were measured during GKS using a thermoluminescent dosimeter. In vivo measurements were also made in 200 patients who underwent GKS with the model C unit for different diagnoses at Na Homolce Hospital. The peripheral dose depended on the collimator size with a logarithmic dependence on collimator size and a linear dependence on the number of shots. This model can be used for the estimation of peripheral doses with a total error less than 20%. This information can help clinicians with treatment planning optimization, especially in patients with long survival expectancy.