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. (August 2018) - Colautti, P.
Highlights: Miniaturized microdosimeters can monitor the dose-mean LET of carbon-ion beams. Four miniaturized microdosimeters have measured on the same beam and same phantom. The y - D values have been compared with Monte Carlo-calculated dose-mean LET values. The four detectors monitor the dose-mean LET with 11% precision up to the distal edge. In the distal edge the monitor precision worsens. Abstract: 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 12 C 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.