Surface dose rate from a flat 106Ru/106Rh episcleral plaque measured with a planar windowless extrapolation chamber and un-laminated EBT3 film

Abstract

In this work, a planar extrapolation chamber without an entrance window was used to measure surface dose rate to water from a flat 106Ru/106Rh plaque manufactured by Eckert & Ziegler BEBIG. Measurements with the flat source were performed as part of a larger aim to develop a convex windowless extrapolation chamber for determining surface dose rate from curved 106Ru/106Rh plaques. Monte Carlo corrections for backscatter and divergence in the chamber were generated with the EGSnrc cavity user code. Surface dose rate values from the extrapolation chamber were compared with un-laminated EBT3 film results based on a 60Co calibration. To determine surface dose using radiochromic film, an additional Monte Carlo correction was needed to account for phantom scatter and volume-averaging within the active layer for the on-contact measurement setup. Additionally, extrapolation chamber results for the flat plaque were compared with scintillation detector measurements performed by the manufacturer. The average surface dose rate from the extrapolation chamber was found to be 1.5% lower than the film measurement result and 8.0% lower than the manufacturer-provided source calibration. Based on the results, it was concluded that a windowless extrapolation chamber can be used as a primary measurement device to determine surface dose rate from a 106Ru/106Rh episcleral plaque, and radiochromic film measurements can also be carried out to serve as an accurate comparison.