Measurement of the peripheral doses for linac stereotactic radiotherapy

The purpose of this study was to establish peripheral doses during stereotactic treatments. The doses to different organs were measured by thermoluminescence dosemeters. A simple power function can describe the relationship between the measured peripheral dose and the distance from target. The dependence of measured peripheral dose at a particular point on the collimator size can also be described by a simple exponential function. Leakage radiation contributes very little to the dose, but becomes dominant at distances of more than 50 cm from the target. The arrangement of arcs as well as the collimator size influence the magnitude of the peripheral dose due to the contribution of exit dose and due to the increasing scattering volume of target. By changing the arc arrangement and using smaller collimators one can reduce the peripheral dose significantly and minimise the total body radiation burden.