An air core cerenkov free scintillation dosimeter: Monte Carlo simulation for external beam radiation therapy

Abstract

We examine the water equivalent properties of two versions of a new type of scintillation optical fibre dosimeter designed for use in external beam applications. The dosimeter has an air core light guide to avoid the generation of a Cerenkov background. The dosimeter has a small sensitive volume and has been designed for use in high dose gradients. One version has a silver coating on the scintillator, while the other has no silver coating. A Monte Carlo (MC) method is used to determine the impact of various structures of the dosimeter on the dose deposited in the sensitive volume. MC is also used to determine the effect of a nearby dosimeter of the same type on the dose deposited, in order to determine the suitability of the dosimeter for array dosimetry. The theoretical predictions are compared to experimental measurements in a 6MV photon beam. We show that the dosimeter is effectively water equivalent when no silver is used on the scintillator, with absolute dose readings in agreement with the control values. When normalised at their maximum, the shape of all depth dose curves is the same as for the water equivalent control. We also show that dosimeter proximity effects are negligible, confirming the suitability of this dosimeter for use in close packed arrays. © 2009 Springer-Verlag.