TU‐F‐BRE‐03: Application of a Novel Mass‐Density Compensation Optimization Method to Improve the Response of a Liquid‐Filled Ionization Chamber in Nonstandard Fields

Abstract

Purpose:To improve the response of the microLion detector (PTW 31018) in small field conditions by optimizing the density of the detector's non‐sensitive components using a novel method based on the detector's dose response function.Methods:The central values h(0,0) of the perturbation functions for the microLion detector and a volume of water equivalent to its sensitive volume were calculated using the Monte Carlo user code egs_chamber by scoring the dose absorbed by a 6 MV photon pencil beam incident on their centroids. Values of h(0,0) were plotted as a function of the density of the microLion's graphite electrode with the detector placed in the axial orientation. The optimized density was found by finding the minimal value of h(0,0).Results:A density of 1.37 g/cm3 was found to minimize the perturbation function of the microLion detector. The modified microLion's response was then evaluated in small square fields with sides in the range of 5 – 40 mm and found to be consistent with highly watere‐quivalent detectors such as a scintillating detector (Exradin W1) and a generic alanine detector in both axial and radial orientations.Conclusion:This work illustrates a novel method which can used to optimize the design of radiation detectors in small fields. This method should also work with other optimization parameters (e.g. thickness of electrode). Density‐compensated detectors have the potential to eliminate the need to evaluate nonstandard field correction factors as described by the IAEA‐AAPM formalism (Alfonso et al.) and simplify future dosimetry protocols for SRS/SBRT modalities. Finally, we also expect an improvement in the response of density‐compensated detectors for composite IMRT fields.