Miniaturized microdosimeters as LET monitors: First comparison of calculated and experimental data performed at the 62 MeV/u 12C beam of INFN-LNS with four different detectors

Purpose The aim of this paper is to investigate the limits of LET monitoring of therapeutic carbon ion beams with miniaturized microdosimetric detectors. Methods Four different miniaturized microdosimeters have been used at the 62 MeV/u 12C beam of INFN Southern National Laboratory (LNS) of Catania for this purpose, i.e. a mini-TEPC and a GEM-microdosimeter, both filled with propane gas, and a silicon and a diamond microdosimeter. The y - D (dose-mean lineal energy) values, measured at different depths in a PMMA phantom, have been compared with LET ¯ D (dose-mean LET) values in water, calculated at the same water-equivalent depth with a Monte Carlo simulation setup based on the GEANT4 toolkit. Results In these first measurements, no detector was found to be significantly better than the others as a LET monitor. The y - D relative standard deviation has been assessed to be 13% for all the detectors. On average, the ratio between y - D and LET ¯ D values is 0.9 ± 0.3, spanning from 0.73 ± 0.08 (in the proximal edge and Bragg peak region) to 1.1 ± 0.3 at the distal edge. Conclusions All the four microdosimeters are able to monitor the dose-mean LET with the 11% precision up to the distal edge. In the distal edge region, the ratio of y - D to LET ¯ D changes. Such variability is possibly due to a dependence of the detector response on depth, since the particle mean-path length inside the detectors can vary, especially in the distal edge region.